IN the immense
class of insects the sexes
sometimes differ in
their locomotive-organs, and
often in their sense-organs,
as in the pectinated and beautifully
plumose antennae of the males
of many species. In Chloeon,
one of the Ephemerae, the male
has great pillared eyes, of which
the female is entirely destitute.*
The ocelli are absent in the
females of certain insects, as
in the Multillidae; and here
the females are likewise wingless.
But we are chiefly concerned
with structures by which one
male is enabled to conquer another,
either in battle or courtship,
through his strength, pugnacity,
ornaments, or music. The innumerable
contrivances, therefore, by which
the male is able to seize the
female, may be briefly passed
over. Besides the complex structures
at the apex of the abdomen, which
ought perhaps to be ranked as
primary organs,*(2) "it is astonishing," as
Mr. B. D. Walsh*(3) has remarked, "how
many different organs are worked
in by nature for the seemingly
insignificant object of enabling
the male to grasp the female
firmly." The mandibles or jaws
are sometimes used for this purpose;
thus the male Corydalis cornutus
(a neuropterous insect in some
degree allied to the dragon flies, &c.)
has immense curved jaws, many
times longer than those of the
female; and they are smooth instead
of being toothed, so that he
is thus enabled to seize her
without injury.*(4) One of the
stag-beetles of North America
(Lucanus elaphus) uses his jaws,
which are much larger than those
of the female, for the same purpose,
but probably likewise for fighting.
In one of the sand-wasps (Ammophila)
the jaws in the two sexes are
closely alike, but are used for
widely different purposes: the
males, as Professor Westwood
observes, "are exceedingly ardent,
seizing their partners round
the neck with their sickle-shaped
jaws";*(5) whilst the females
use these organs for burrowing
in sand-banks and making their
nests.
* Sir J. Lubbock, Transact.
Linnean Soc., vol. xxv, 1866,
p. 484. With respect to the Mutillidae,
see Westwood, Modern Class. of
Insects, vol. ii., p. 213.
*(2) These organs in the male
often differ in closely-allied
species, and afford excellent
specific characters. But their
importance, from a functional
point of view, as Mr. R. MacLachlan
has remarked to me, has probably
been overrated. It has been suggested,
that slight differences in these
organs would suffice to prevent
the intercrossing of well-marked
varieties or incipient species,
and would thus aid in their development.
That this can hardly be the case,
we may infer from the many recorded
cases (see, for instance, Bronn,
Geschichte der Natur, B. ii.,
1843, s. 164; and Westwood, Transact.
Ent. Soc., vol. iii., 1842, p.
195) of distinct species having
been observed in union. Mr. MacLachlan
informs me (vide Stett. Ent.
Zeitung, 1867, s. 155) that when
several species of Phryganidae,
which present strongly-pronounced
differences of this kind, were
confined together by Dr. Aug.
Meyer, they coupled, and one
pair produced fertile ova.
*(3) The Practical Entomologist,
Philadelphia, vol. ii., May,
1867, p 88.
*(4) Mr. Walsh, ibid., p. 107.
*(5) Modern Classification of
Insects, vol. ii., 1840, pp.
205, 206. Mr. Walsh, who called
my attention to the double use
of the jaws, says that he has
repeatedly observed this fact.
The tarsi of
the front-legs are dilated
in many male beetles,
or are furnished with broad cushions
of hairs; and in many genera
of water-beetles they are armed
with a round flat sucker, so
that the male may adhere to the
slippery body of the female.
It is a much more unusual circumstance
that the females of some water-beetles
(Dytiscus) have their elytra
deeply grooved, and in Acilius
sulcatus thickly set with hairs,
as an aid to the male. The females
of some other water-beetles (Hydroporus)
have their elytra punctured for
the same purpose.* In the male
of Crabrocribrarius (see fig.
9), it is the tibia which is
dilated into a broad horny plate,
with minute membraneous dots,
giving to it a singular appearance
like that of a riddle.*(2) In
the male of Penthe (a genus of
beetles) a few of the middle
joints of the antennae are dilated
and furnished on the inferior
surface with cushions of hair,
exactly like those on the tarsi
of the Carabidae, "and obviously
for the same end." In male dragon-flies, "the
appendages at the tip of the
tail are modified in an almost
infinite variety of curious patterns
to enable them to embrace the
neck of the female." Lastly,
in the males of many insects,
the legs are furnished with peculiar
spines, knobs or spurs; or the
whole leg is bowed or thickened,
but this is by no means invariably
a sexual character; or one pair,
or all three pairs are elongated,
sometimes to an extravagant length.*(3)
* We have here a curious and
inexplicable case of dimorphism,
for some of the females of four
European species of Dysticus,
and of certain species of Hydroporus,
have their elytra smooth; and
no intermediate gradations between
the sulcated or punctured, and
the quite smooth elytra have
been observed. See Dr. H. Schaum,
as quoted in the Zoologist, vols.
v.-vi., 1847-48, p. 1896. Also
Kirby and Spence, Introduction
to Entomology, vol. iii., 1826,
p. 305.
*(2) Westwood, Modern Class.,
vol. ii., p. 193. The following
statement about Penthe, and others
in inverted commas, are taken
from Mr. Walsh, Practical Entomologist,
Philadelphia, vol. iii., p. 88.
*(3) Kirby and
Spence, Introduct. &c.,
vol. iii., pp. 332-336.
The sexes of many species in
all the orders present differences,
of which the meaning is not understood.
One curious case is that of a
beetle (see fig. 10), the male
of which has left mandible much
enlarged; so that the mouth is
greatly distorted. In another
carabidous beetle, Eurygnathus,*
we have the case, unique as far
as known to Mr. Wollaston, of
the head of the female being
much broader and larger, though
in a variable degree, than that
of the male. Any number of such
cases could be given. They abound
in the Lepidoptera: one of the
most extraordinary is that certain
male butterflies have their fore-legs
more or less atrophied, with
the tibiae and tarsi reduced
to mere rudimentary knobs. The
wings, also, in the two sexes
often differ in neuration,*(2)
and sometimes considerably in
outline, as in the Aricoris epitus,
which was shewn to me in the
British Museum by Mr. A. Butler.
The males of certain South American
butterflies have tufts of hair
on the margins of the wings,
and horny excrescences on the
discs of the posterior pair.*(3)
In several British butterflies,
as shewn by Mr. Wonfor, the males
alone are in parts clothed with
peculiar scales.
* Insecta Maderensia, 1854,
page 20.
*(2) E. Doubleday, Annals and
Mag. of Nat. Hist., vol. i.,
1848, p. 379. I may add that
the wings in certain Hymenoptera
(see Shuckard, Fossorial Hymenoptera,
1837, pp. 39-43) differ in neuration
according to sex.
*(3) H. W. Bates, in Journal
of Proc. Linn. Soc., vol. vi.,
1862, p. 74. Mr. Wonfor's observations
are quoted in Popular Science
Review, 1868, p. 343.
The use of the bright light
of the female glow-worm has been
subject to much discussion. The
male is feebly luminous, as are
the larvae and even the eggs.
It has been supposed by some
authors that the light serves
to frighten away enemies, and
by others to guide the male to
the female. At last, Mr. Belt*
appears to have solved the difficulty:
he finds that all the Lampyridae
which he has tried are highly
distasteful to insectivorous
mammals and birds. Hence it is
in accordance with Mr. Bates'
view, hereafter to be explained,
that many insects mimic the Lampyridae
closely, in order to be mistaken
for them, and thus to escape
destruction. He further believes
that the luminous species profit
by being at once recognised as
unpalatable. It is probable that
the same explanation may be extended
to the elaters, both sexes of
which are highly luminous. It
is not known why the wings of
the female glow-worm have not
been developed; but in her present
state she closely resembles a
larva, and as larvae are so largely
preyed on by many animals, we
can understand why she has been
rendered so much more luminous
and conspicuous than the male;
and why the larvae themselves
are likewise luminous.
* The Naturalist in Nicaragua,
1874, pp. 316-320. On the phosphorescence
of the eggs, see Annals and Magazine
of Natural History, Nov., 1871,
p. 372.
Difference in
Size between the Sexes.- With
insects of all kinds
the males are commonly smaller
than the females; and this difference
can often be detected even in
the larval state. So considerable
is the difference between the
male and female cocoons of the
silk-moth (Bombyx mori), that
in France they are separated
by a particular mode of weighing.*
In the lower classes of the animal
kingdom, the greater size of
the females seems generally to
depend on their developing an
enormous number of ova; and this
may to a certain extent hold
good with insects. But Dr. Wallace
has suggested a much more probable
explanation. He finds, after
carefully attending to the development
of the caterpillars of Bombyx
cynthia and yamamai, and especially
to that of some dwarfed caterpillars
reared from a second brood on
unnatural food, "that in proportion
as the individual moth is finer,
so is the time required for its
metamorphosis longer; and for
this reason the female, which
is the larger and heavier insect,
from having to carry her numerous
eggs, will be preceded by the
male, which is smaller and has
less to mature."*(2) Now as most
insects are short-lived, and
as they are exposed to many dangers,
it would manifestly be advantageous
to the female to be impregnated
as soon as possible. This end
would be gained by the males
being first matured in large
numbers ready for the advent
of the females; and this again
would naturally follow, as Mr.
A. R. Wallace has remarked,*(3)
through natural selection; for
the smaller males would be first
matured, and thus would procreate
a large number of offspring which
would inherit the reduced size
of their male parents, whilst
the larger males from being matured
later would leave fewer offspring.
* Robinet, Vers a Soie, 1848,
p. 207.
*(2) Transact. Ent. Soc., 3rd
series, vol. v., p. 486.
*(3) Journal of Proc. Ent. Soc.,
Feb. 4, 1867, p. lxxi.
There are, however, exceptions
to the rule of male insects being
smaller than the females: and
some of these exceptions are
intelligible. Size and strength
would be an advantage to the
males, which fight for the possession
of the females; and in these
cases, as with the stagbeetle
(Lucanus), the males are larger
than the females. There are,
however, other beetles which
are not known to fight together,
of which the males exceed the
females in size; and the meaning
of this fact is not known; but
in some of these cases, as with
the huge Dynastes and Megasoma,
we can at least see that there
would be no necessity for the
males to be smaller than the
females, in order to be matured
before them, for these beetles
are not short-lived, and there
would be ample time for the pairing
of the sexes. So again, male
dragon-flies (Libellulidae) are
sometimes sensibly larger, and
never smaller, than the females;*
and as Mr. MacLachlan believes,
they do not generally pair with
the females until a week or fortnight
has elapsed, and until they have
assumed their proper masculine
colours. But the most curious
case, shewing on what complex
and easily-overlooked relations,
so trifling a character as difference
in size between the sexes may
depend, is that of the aculeate
Hymenoptera; for Mr. F. Smith
informs me that throughout nearly
the whole of this large group,
the males, in accordance with
the general rule, are smaller
than the females, and emerge
about a week before them; but
amongst the bees, the males of
Apis mellifica, Anthidium manicatum,
and Anthophora acervorum, and
amongst the fosseres, the males
of the Methoca ichneumonides,
are larger than the females.
The explanation of this anomaly
is that a marriage flight is
absolutely necessary with these
species, and the male requires
great strength and size in order
to carry the female through the
air. Increased size has here
been acquired in opposition to
the usual relation between size
and the period of development,
for the males, though larger,
emerge before the smaller females.
* For this and other statements
on the size of the sexes, see
Kirby and Spence, ibid., vol.
iii., p. 300; on the duration
of life in insects, see p. 344.
We will now review the several
Orders, selecting such facts
as more particularly concern
us. The Lepidoptera (butterflies
and moths) will be retained for
a separate chapter.
Order: THYSANURA.-
The members of this lowly organised
order
are wingless, dull-coloured,
minute insects, with ugly, almost
mis-shapen heads and bodies.
Their sexes do not differ, but
they are interesting as shewing
us that the males pay sedulous
court to the females even low
down in the animal scale. Sir
J. Lubbock* says: "It is very
amusing to see these little creatures
(Smynthurus luteus) coquetting
together. The male, which is
much smaller than the female,
runs round her, and they butt
one another, standing face to
face and moving backward and
forward like two playful lambs.
Then the female pretends to run
away and the male runs after
her with a queer appearance of
anger, gets in front and stands
facing her again; then she turns
coyly round, but he, quicker
and more active, scuttles round
too, and seems to whip her with
his antennae; then for a bit
they stand face to face, play
with their antennae, and seem
to be all in all to one another."
* Transact. Linnean Soc., vol.
xxvi., 1868, p. 296.
Order: DIPTERA (Flies).- The
sexes differ little in colour.
The greatest difference, known
to Mr. F. Walker, is in the genus
Bibio, in which the males are
blackish or quite black, and
the females obscure brownish-orange.
The genus Elaphomyia, discovered
by Mr. Wallace* in New Guinea,
is highly remarkable, as the
males are furnished with horns,
of which the females are quite
destitute. The horns spring from
beneath the eyes, and curiously
resemble those of a stag, being
either branched or palmated.
In one of the species, they equal
the whole body in length. They
might be thought to be adapted
for fighting, but as in one species
they are of a beautiful pink
colour, edged with black, with
a pale central stripe, and as
these insects have altogether
a very elegant appearance, it
is perhaps more probable that
they serve as ornaments. That
the males of some Diptera fight
together is certain; Prof. Westwood*(2)
has several times seen this with
the Tipulae. The males of other
Diptera apparently try to win
the females by their music: H.
Muller*(3) watched for some time
two males of an Eristalis courting
a female; they hovered above
her, and flew from side to side,
making a high humming noise at
the same time. Gnats and mosquitoes
(Culicidae) also seem to attract
each other by humming; and Prof.
Mayer has recently ascertained
that the hairs on the antennae
of the male vibrate in unison
with the notes of a tuning-fork,
within the range of the sounds
emitted by the female. The longer
hairs vibrate sympathetically
with the graver notes, and the
shorter hairs with the higher
ones. Landois also asserts that
he has repeatedly drawn down
a whole swarm of gnats by uttering
a particular note. It may be
added that the mental faculties
of the Diptera are probably higher
than in most other insects, in
accordance with their highly-developed
nervous System.*(4)
* The Malay Archipelago, vol.
ii., 1869, p. 313.
*(2) Modern Classification of
Insects, vol. ii., 1840, p. 526.
*(3) "Anwendung," &c.,
Verh. d. n. V. Jahrg. xxix.
p. 80.
Mayer, in American Naturalist,
1874, p. 236.
*(4) See Mr.
B. T. Lowne's interesting work,
On the Anatomy of the Blowfly,
Musca vomitoria, 1870, p. 14.
He remarks (p. 33) that, "the
captured flies utter a peculiar
plaintive note, and that this
sound causes other flies to disappear."
Order: HEMIPTERA (Field-Bugs).-
Mr. J. W. Douglas, who has particularly
attended to the British species,
has kindly given me an account
of their sexual differences.
The males of some species are
furnished with wings, whilst
the females are wingless; the
sexes differ in the form of their
bodies, elytra, antennae and
tarsi; but as the signification
of these differences is unknown,
they may be here passed over.
The females are generally larger
and more robust than the males.
With British, and, as far as
Mr. Douglas knows, with exotic
species, the sexes do not commonly
differ much in colour; but in
about six British species the
male is considerably darker than
the female, and in about four
other species the female is darker
than the male. Both sexes of
some species are beautifully
coloured; and as these insects
emit an extremely nauseous odour,
their conspicuous colours may
serve as a signal that they are
unpalatable to insectivorous
animals. In some few cases their
colours appear to be directly
protective: thus Prof. Hoffmann
informs me that he could hardly
distinguish a small pink and
green species from the buds on
the trunks of lime-trees, which
this insect frequents.
Some species of Reduvidae make
a stridulating noise; and, in
the case of Pirates stridulus,
this is said* to be effected
by the movement of the neck within
the prothoracic cavity. According
to Westring, Reduvius personatus
also stridulates. But I have
no reason to suppose that this
is a sexual character, excepting
that with non-social insects
there seems to be no use for
sound-producing organs, unless
it be as a sexual call.
* Westwood, Modern Classification
of Insects, vol. ii., p. 473.
Order: HOMOPTERA.-
Every one who has wandered
in a tropical
forest must have been astonished
at the din made by the male Cicadae.
The females are mute; as the
Grecian poet Xenarchus says, "Happy
the cicadas live, since they
all have voiceless wives." The
noise thus made could be plainly
heard on board the Beagle, when
anchored at a quarter of a mile
from the shore of Brazil; and
Captain Hancock says it can be
heard at the distance of a mile.
The Greeks formerly kept, and
the Chinese now keep these insects
in cages for the sake of their
song, so that it must be pleasing
to the ears of some men.* The
Cicadidae usually sing during
the day, whilst the Fulgoridae
appear to be night-songsters.
The sound, according to Landois,*(2)
is produced by the vibration
of the lips of the spiracles,
which are set into motion by
a current of air emitted from
the tracheae; but this view has
lately been disputed. Dr. Powell
appears to have proved*(3) that
it is produced by the vibration
of a membrane, set into action
by a special muscle. In the living
insect, whilst stridulating,
this membrane can be seen to
vibrate; and in the dead insect
the proper sound is heard, if
the muscle, when a little dried
and hardened, is pulled with
the point of a pin. In the female
the whole complex musical apparatus
is present, but is much less
developed than in the male, and
is never used for producing sound.
* These particulars are taken
from Westwood's Modern Classification
of Insects, vol. ii., 1840, p.
422. See, also, on the Fulgoridae,
Kirby and Spence, Introduct.,
vol. ii., p. 401.
*(2) Zeitschrift fur wissenschaft
Zoolog., B. xvii., 1867, ss.
152-158.
*(3) Transactions of the New
Zealand Institute, vol. v., 1873,
p. 286.
With respect
to the object of the music.
Dr. Hartman, in speaking
of the Cicada septemdecim of
the United States, says,* "The
drums are now (June 6th and 7th,
1851) heard in all directions.
This I believe to be the martial
summons from the males. Standing
in thick chestnut sprouts about
as high as my head, where hundreds
were around me, I observed the
females coming around the drumming
males." He adds, "This season
(Aug. 1868) a dwarf pear tree
in my garden produced about fifty
larvae of C. pruinosa; and I
several times noticed the females
to alight near a male while he
was uttering his clanging notes." Fritz
Muller writes to me from S. Brazil
that he has often listened to
a musical contest between two
or three males of a species with
a particularly loud voice, seated
at a considerable distance from
each other: as soon as one had
finished his song, another immediately
begun, and then another. As there
is so much rivalry between the
males, it is probable that the
females not only find them by
their sounds, but that, like
female birds, they are excited
or allured by the male with the
most attractive voice.
* I am indebted to Mr. Walsh
for having sent me this extract
from A Journal of the Doings
of Cicada septemdecim, by Dr.
Hartman.
I have not heard of any well-marked
cases of ornamental differences
between the sexes of the Homoptera.
Mr. Douglas informs me that there
are three British species, in
which the male is black or marked
with black bands, whilst the
females are pale-coloured or
obscure.
Order: ORTHOPTERA
(Crickets and Grasshoppers).-
The males
in the three saltatorial families
in this Order are remarkable
for their musical powers, namely
the Achetidae or crickets, the
Locustidae for which there is
no equivalent English name, and
the Acridiidae or grasshoppers.
The stridulation produced by
some of the Locustidae is so
loud that it can be heard during
the night at the distance of
a mile;* and that made by certain
species is not unmusical even
to the human ear, so that the
Indians on the Amazons keep them
in wicker cages. All observers
agree that the sounds serve either
to call or excite the mute females.
With respect to the migratory
locusts of Russia, Korte has
given*(2) an interesting case
of selection by the female of
a male. The males of this species
(Pachytylus migratorius) whilst
coupled with the female stridulate
from anger or jealousy, if approached
by other males. The house-cricket
when surprised at night uses
its voice to warn its fellows.*(3)
In North America the katydid
(Platyphyllum concavum, one of
the Locustidae) is described*(4)
as mounting on the upper branches
of a tree, and in the evening
beginning "his noisy babble,
while rival notes issue from
the neighbouring trees, and the
graves resound with the call
of Katy-did-she-did the live-long
night." Mr. Bates, in speaking
of the European field-cricket
(one of the Achetidae), says "the
male has been observed to place
himself in the evening at the
entrance of his burrow, and stridulate
until a female approaches, when
the louder notes are succeeded
by a more subdued tone, whilst
the successful musician caresses
with his antennae the mate he
has won."*(5) Dr. Scudder was
able to excite one of these insects
to answer him, by rubbing on
a file with a quill.*(6) In both
sexes a remarkable auditory apparatus
has been discovered by von Siebold,
situated in the front legs.*(7)
* L. Guilding, Transactions
of the Linnean Society, vol.
xv., p. 154.
*(2) I state
this on the authority of Koppen, "Uber die Heuschrecken
in Sudrussland," 1866, p. 32,
for I have in vain endeavoured
to procure Korte's work.
*(3) Gilbert White, Natural
History of Selborne, vol. ii.,
1825, p. 262.
*(4) Harris, Insects of New
England, 1842, p. 128.
*(5) The Naturalist on the Amazons,
vol. i., 1863, p. 252. Mr. Bates
gives a very interesting discussion
on the gradations in the musical
apparatus of the three families.
See also Westwood, Modern Classification
of Insects, vol. ii., pp. 445
and 453.
*(6) Proceedings of the Boston
Society of Natural History, vol.
xi., April, 1868.
*(7) Nouveau Manuel d'Anat.
Comp., French translat., tom.
1, 1850, p. 567.
In the three families the sounds
are differently produced. In
the males of the Achetidae both
wing-covers have the same apparatus;
and this in the field cricket
(see Gryllus campestris, fig.
11) consists, as described by
Landois,* of from 131 to 138
sharp, transverse ridges or teeth
(st) on the under side of one
of the nervures of the wing-cover.
This toothed nervure is rapidly
scraped across a projecting,
smooth, hard nervure (r) on the
upper surface of the opposite
wing. First one wing is rubbed
over the other, and then the
movement is reversed. Both wings
are raised a little at the same
time, so as to increase the resonance.
In some species the wing-covers
of the males are furnished at
the base with a talc-like plate.*(2)
I here give a drawing (see fig.
12) of the teeth on the under
side of the nervure of another
species of Gryllus, viz., G.
domesticus. With respect to the
formation of these teeth, Dr.
Gruber has shown*(3) that they
have been developed by the aid
of selection, from the minute
scales and hairs with which the
wings and body are covered, and
I came to the same conclusion
with respect to those of the
Coleoptera. But Dr. Gruber further
shews that their development
is in part directly due to the
stimulus from the friction of
one wing over the other.
* Zeitschrift fur wissenschaft.
Zoolog., B. xvii., 1867, s. 117.
*(2) Westwood, Modern Classification
of Insects, vol. i., p. 440.
*(3) "Uber der Tonapparat der
Locustiden, ein Beitrage zum
Darwinismus," Zeitschrift fur
wissenschaft. Zoolog., B. xxii.,
1872, p. 100.
In the Locustidae
the opposite wing-covers differ
from each
other in structure (see fig.
13), and the action cannot, as
in the last family, be reversed.
The left wing, which acts as
the bow, lies over the right
wing which serves as the fiddle.
One of the nervures (a) on the
under surface of the former is
finely serrated, and is scraped
across the prominent nervures
on the upper surface of the opposite
or right wing. In our British
Phasgonura viridissima it appeared
to me that the serrated nervure
is rubbed against the rounded
hind-corner of the opposite wing,
the edge of which is thickened,
coloured brown, and very sharp.
In the right wing, but not in
the left, there is a little plate,
as transparent as talc, surrounded
by nervures, and called the speculum.
In Ephippiger vitium, a member
of this same family, we have
a curious subordinate modification;
for the wing-covers are greatly
reduced in size, but "the posterior
part of the pro-thrax is elevated
into a kind of dome over the
wing-covers, and which has probably
the effect of increasing the
sound."*
* Westwood Modern Classification
of Insects, vol. i., p. 453.
We thus see that the musical
apparatus is more differentiated
or specialised in the Locustidae
(which include, I believe, the
most powerful performers in the
Order), than in the Achetidae,
in which both wing-covers have
the same structure and the same
function.* Landois, however,
detected in one of the Locustidae,
namely in Decticus, a short and
narrow row of small teeth, mere
rudiments, on the inferior surface
of the right wing-cover, which
underlies the other and is never
used as the bow. I observed the
same rudimentary structure on
the under side of the right wing-cover
in Phasgonura viridissima. Hence
we may infer with confidence
that the Locustidae are descended
from a form, in which, as in
the existing Achetidae, both
wing-covers had serrated nervures
on the under surface, and could
be indifferently used as the
bow; but that in the Locustidae
the two wing-covers gradually
became differentiated and perfected,
on the principle of the division
of labour, the one to act exclusively
as the bow, and the other as
the fiddle. Dr. Gruber takes
the same view, and has shewn
that rudimentary teeth are commonly
found on the inferior surface
of the right wing. By what steps
the more simple apparatus in
the Achetidae originated, we
do not know, but it is probable
that the basal portions of the
wing-covers originally overlapped
each other as they do at present;
and that the friction of the
nervures produced a grating sound,
as is now the case with the wing-covers
of the females.*(2) A grating
sound thus occasionally and accidentally
made by the males, if it served
them ever so little as a love-call
to the females, might readily
have been intensified through
sexual selection, by variations
in the roughness of the nervures
having been continually preserved.
* Landois, Zeitschrift fur wissenschaft.
Zoolog., B. xvii., 1867, ss.
121, 122.
*(2) Mr. Walsh
also informs me that he has
noticed that the
female of the Platyphyllum concavum, "when
captured makes a feeble grating
noise by shuffling her wing-covers
together."
In the last
and third family, namely the
Acridiidae or grasshoppers,
the stridulation is produced
in a very different manner, and
according to Dr. Scudder, is
not so shrill as in the preceding
families. The inner surface of
the femur (see fig. 14, r) is
furnished with a longitudinal
row of minute, elegant, lancet-shaped,
elastic teeth, from 85 to 93
in number;* and these are scraped
across the sharp, projecting
nervures on the wing-covers,
which are thus made to vibrate
and resound. Harris*(2) says
that when one of the males begins
to play, he first "bends the
shank of the hind-leg beneath
the thigh, where it is lodged
in a furrow designed to receive
it, and then draws the leg briskly
up and down. He does not play
both fiddles together, but alternately,
first upon one and then on the
other." In many species, the
base of the abdomen is hollowed
out into a great cavity which
is believed to act as a resounding
board. In Pneumora (see fig.
15), a S. African genus belonging
to the same family, we meet with
a new and remarkable modification;
in the males a small notched
ridge projects obliquely from
each side of the abdomen, against
which the hind femora are rubbed.*(3)
As the male is furnished with
wings (the female being wingless),
it is remarkable that the thighs
are not rubbed in the usual manner
against the wing-covers; but
this may perhaps be accounted
for by the unusually small size
of the hind-legs. I have not
been able to examine the inner
surface of the thighs, which,
judging from analogy, would be
finely serrated. The species
of Pneumora have been more profoundly
modified for the sake of stridulation
than any other orthopterous insect;
for in the male the whole body
has been converted into a musical
instrument, being distended with
air, like a great pellucid bladder,
so as to increase the resonance.
Mr. Trimen informs me that at
the Cape of Good Hope these insects
make a wonderful noise during
the night.
* Landois, ibid., s. 113.
*(2) Insects of New England,
1842, p. 133.
*(3) Westwood, Modern Classification,
vol i., p. 462.
In the three foregoing families,
the females are almost always
destitute of an efficient musical
apparatus. But there are a few
exceptions to this rule, for
Dr. Gruber has shewn that both
sexes of Ephippiger vitium are
thus provided; though the organs
differ in the male and female
to a certain extent. Hence we
cannot suppose that they have
been transferred from the male
to the female, as appears to
have been the case with the secondary
sexual characters of many other
animals. They must have been
independently developed in the
two sexes, which no doubt mutually
call to each other during the
season of love. In most other
Locustidae (but not, according
to Landois, in Decticus) the
females have rudiments of the
stridulatory organs proper to
the male; from whom it is probable
that these have been transferred.
Landois also found such rudiments
on the under surface of the wing-covers
of the female Achetidae, and
on the femora of the female Acridiidae.
In the Homoptera, also, the females
have the proper musical apparatus
in a functionless state; and
we shall hereafter meet in other
divisions of the animal kingdom
with many instances of structures
proper to the male being present
in a rudimentary condition of
the female.
Landois has observed another
important fact, namely, that
in the females of the Acridiidae,
the stridulating teeth on the
femora remain throughout life
in the same condition in which
they first appear during the
larval state in both sexes. In
the males, on the other hand,
they become further developed,
and acquire their perfect structure
at the last moult, when the insect
is mature and ready to breed.
From the facts
now given, we see that the
means by which the
males of the Orthoptera produce
their sounds are extremely diversified,
and are altogether different
from those employed by the Homoptera.*
But throughout the animal kingdom
we often find the same object
gained by the most diversified
means; this seems due to the
whole organisation having undergone
multifarious changes in the course
of ages, and as part after part
varied different variations were
taken advantage of for the same
general purpose. The diversity
of means for producing sound
in the three families of the
Orthoptera and in the Homoptera,
impresses the mind with the high
importance of these structures
to the males, for the sake of
calling or alluring the females.
We need feel no surprise at the
amount of modification which
the Orthoptera have undergone
in this respect, as we now know,
from Dr. Scudder's remarkable
discovery,*(2) that there has
been more than ample time. This
naturalist has lately found a
fossil insect in the Devonian
formation of New Brunswick, which
is furnished with "the well-known
tympanum or stridulating apparatus
of the male Locustidae." The
insect, though in most respects
related to the Neuroptera, appears,
as is so often the case with
very ancient forms, to connect
the two related Orders of the
Neuroptera and Orthoptera.
* Landois has recently found
in certain Orthoptera rudimentary
structures closely similar to
the sound-producing organs in
the Homoptera; and this is a
surprising fact. See Zeitschrift
fur wissenschaft. Zoolog., B.
xxii., Heft 3, 1871, p. 348.
*(2) Transactions, Entomological
Society, 3rd series, vol. ii.
(Journal of Proceedings, p. 117).
I have but little
more to say on the Orthoptera.
Some of the
species are very pugnacious:
when two male field-crickets
(Gryllus campestris) are confined
together, they fight till one
kills the other; and the species
of mantis are described as manoeuvring
with their swordlike front-limbs,
like hussars with their sabres.
The Chinese keep these insects
in little bamboo cages, and match
them like game-cocks.* With respect
to colour, some exotic locusts
are beautifully ornamented; the
posterior wings being marked
with red, blue, and black; but
as throughout the Order the sexes
rarely differ much in colour,
it is not probable that they
owe their bright tints to sexual
selection. Conspicuous colours
may be of use to these insects,
by giving notice that they are
unpalatable. Thus it has been
observed*(2) that a bright-coloured
Indian locust was invariably
rejected when offered to birds
and lizards. Some cases, however,
are known of sexual differences
in colour in this Order. The
male of an American cricket*(3)
is described as being as white
as ivory, whilst the female varies
from almost white to greenish-yellow
or dusky. Mr. Walsh informs me
that the adult male of Spectrum
femoratum (one of the Phasmidae) "is
of a shining brownish-yellow
colour; the adult female being
of a dull, opaque, cinereous
brown; the young of both sexes
being green." Lastly, I may mention
that the male of one curious
kind of cricket*(4) is furnished
with "a long membranous appendage,
which falls over the face like
a veil"; but what its use may
be, is not known.
* Westwood, Modern Classification
of Insects, vol. i., p. 427;
for crickets, p. 445.
*(2) Mr. Ch. Horne, in Proceedings
of the Entomological Society,
May 3, 1869, p. xii.
*(3) "The Oecanthus nivalis," Harris,
Insects of New England, 1842,
p. 124. The two sexes of OE.
pellucidus of Europe differ,
as I hear from Victor Carus,
in nearly the same manner.
*(4) Platyblemnus: Westwood,
Modern Classification, vol. i.,
p. 447.
Order: NEUROPTERA.-
Little need here be said, except
as to colour.
In the Ephemeridae the sexes
often differ slightly in their
obscure tints;* but it is not
probable that the males are thus
rendered attractive to the females.
The Libellulidae, or dragon-flies,
are ornamented with splendid
green, blue, yellow, and vermilion
metallic tints; and the sexes
often differ. Thus, as Prof.
Westwood remarks,*(2) the males
of some of the Agrionidae, "are
of a rich blue with black wings,
whilst the females are fine green
with colourless wings." But in
Agrion ramburii these colours
are exactly reversed in the two
sexes.*(3) In the extensive N.
American genus of Hetaerina,
the males alone have a beautiful
carmine spot at the base of each
wing. In Anax junius the basal
part of the abdomen in the male
is a vivid ultramarine blue,
and in the female grass-green.
In the allied genus Gomphus,
on the other hand, and in some
other genera, the sexes differ
but little in colour. In closely-allied
forms throughout the animal kingdom,
similar cases of the sexes differing
greatly, or very little, or not
at all, are of frequent occurrence.
Although there is so wide a difference
in colour between the sexes of
many Libellulidae, it is often
difficult to say which is the
more brilliant; and the ordinary
coloration of the two sexes is
reversed, as we have just seen,
in one species of Agrion. It
is not probable that their colours
in any case have been gained
as a protection. Mr. MacLachlan,
who has closely attended to this
family, writes to me that dragon-flies-
the tyrants of the insect-world-
are the least liable of any insect
to be attacked by birds or other
enemies, and he believes that
their bright colours serve as
a sexual attraction. Certain
dragon-flies apparently are attracted
by particular colours: Mr. Patterson
observed*(4) that the Agrionidae,
of which the males are blue,
settled in numbers on the blue
float of a fishing line; whilst
two other species were attracted
by shining white colours.
* B. D. Walsh,
the "Pseudo-neuroptera
of Illinois," in Proceedings
of the Entomological Society
of Philadelphia, 1862, p. 361.
*(2) Modern Classification,
vol. ii., p. 37.
*(3) Walsh, ibid., p. 381. I
am indebted to this naturalist
for the following facts on Hetaerina,
Anax, and Gomphus.
*(4) Transactions, Ent. Soc.,
vol. i., 1836, p. lxxxi.
It is an interesting fact, first
noticed by Schelver, that, in
several genera belonging to two
sub-families, the males on first
emergence from the pupal state,
are coloured exactly like the
females; but that their bodies
in a short time assume a conspicuous
milky-blue tint, owing to the
exudation of a kind of oil, soluble
in ether and alcohol. Mr. MacLachlan
believes that in the male of
Libellula depressa this change
of colour does not occur until
nearly a fortnight after the
metamorphosis, when the sexes
are ready to pair.
Certain species
of Neurothemis present, according
to Brauer,*
a curious case of dimorphism,
some of the females having ordinary
wings, whilst others have them "very
richly netted, as in the males
of the same species." Brauer "explains
the phenomenon on Darwinian principles
by the supposition that the close
netting of the veins is a secondary
sexual character in the males,
which has been abruptly transferred
to some of the females, instead
of, as generally occurs, to all
of them." Mr. MacLachlan informs
me of another instance of dimorphism
in several species of Agrion,
in which some individuals are
of an orange colour, and these
are invariably females. This
is probably a case of reversion;
for in the true Libellulae, when
the sexes differ in colour, the
females are orange or yellow;
so that supposing Agrion to be
descended from some primordial
form which resembled the typical
Libellulae in its sexual characters,
it would not be surprising that
a tendency to vary in this manner
should occur in the females alone.
* See abstract in the Zoological
Record for 1867, p. 450.
Although many
dragon-flies are large, powerful,
and fierce insects,
the males have not been observed
by Mr. MacLachlan to fight together,
excepting, as he believes, in
some of the smaller species of
Agrion. In another group in this
Order, namely, the termites or
white ants, both sexes at the
time of swarming may be seen
running about, "the male after
the female, sometimes two chasing
one female, and contending with
great eagerness who shall win
the prize."* The Atropos pulsatorius
is said to make a noise with
its jaws, which is answered by
other individuals.*(2)
* Kirby and Spence, Introduction
to Entomology, vol. ii., 1818,
p. 35.
*(2) Houzeau, Etudes sur Les
Facultes Mentales des Animaux,
tom. i., p. 104.
Order: HYMENOPTERA.-
That inimitable observer, M.
Fabre,* in describing
the habits of Cerceris, a wasp-like
insect, remarks that "fights
frequently ensue between the
males for the possession of some
particular female, who sits,
an apparently unconcerned beholder
of the struggle for supremacy,
and when the victory is decided,
quietly flies away in company
with the conqueror." Westwood*(2)
says that the males of one of
the saw-flies (Tenthredinae) "have
been found fighting together,
with their mandibles locked." As
M. Fabre speaks of the males
of Cerceris striving to obtain
a particular female, it may be
well to bear in mind that insects
belonging to this Order have
the power of recognising each
other after long intervals of
time, and are deeply attached.
For instance, Pierre Huber, whose
accuracy no one doubts, separated
some ants, and when, after an
interval of four months, they
met others which had formerly
belonged to the same community,
they recognised and caressed
one another with their antennae.
Had they been strangers they
would have fought together. Again,
when two communities engage in
a battle, the ants on the same
side sometimes attack each other
in the general confusion, but
they soon perceive their mistake,
and the one ant soothes the other.*(3)
* See an interesting
article, "The
Writings of Fabre," in Nat. Hist.
Review, April, 1862, p. 122.
*(2) Journal of Proceedings
of Entomological Society, Sept.
7, 1863, p. 169.
*(3) P. Huber, Recherches sur
les Moeurs des Fourmis, 1810,
pp. 150,165.
In this Order slight differences
in colour, according to sex,
are common, but conspicuous differences
are rare except in the family
of bees; yet both sexes of certain
groups are so brilliantly coloured-
for instance in Chrysis, in which
vermilion and metallic greens
prevail- that we are tempted
to attribute the result to sexual
selection. In the Ichneumonidae,
according to Mr. Walsh,* the
males are almost universally
lighter-coloured than the females.
On the other hand, in the Tenthredinidae
the males are generally darker
than the females. In the Siricidae
the sexes frequently differ;
thus the male of Sirex juvencus
is banded with orange, whilst
the female is dark purple; but
it is difficult to say which
sex is the more ornamented. In
Tremex columboe the female is
much brighter coloured than the
male. I am informed by Mr. F.
Smith, that the male ants of
several species are black, the
females being testaceous.
* Proceedings of the Entomological
Society of Philadelphia, 1866,
pp. 238, 239.
In the family of bees, especially
in the solitary species, as I
hear from the same entomologist,
the sexes often differ in colour.
The males are generally the brighter,
and in Bombus as well as in Apathus,
much more variable in colour
than the females. In Anthophora
retusa the male is of a rich
fulvous-brown, whilst the female
is quite black: so are the females
of several species of Xylocopa,
the males being bright yellow.
On the other hand the females
of some species, as of Andraena
fulva, are much brighter coloured
than the males. Such differences
in colour can hardly be accounted
for by the males being defenceless
and thus requiring protection,
whilst the females are well defended
by their stings. H. Muller,*
who has particularly attended
to the habits of bees, attributes
these differences in colour in
chief part to sexual selection.
That bees have a keen perception
of colour is certain. He says
that the males search eagerly
and fight for the possession
of the females; and he accounts
through such contests for the
mandibles of the males being
in certain species larger than
those of the females. In some
cases the males are far more
numerous than the females, either
early in the season, or at all
times and places, or locally;
whereas the females in other
cases are apparently in excess.
In some species the more beautiful
males appear to have been selected
by the females; and in others
the more beautiful females by
the males. Consequently in certain
genera (Muller, p. 42), the males
of the several species differ
much in appearance, whilst the
females are almost indistinguishable;
in other genera the reverse occurs.
H. Muller believes (p. 82) that
the colours gained by one sex
through sexual selection have
often been transferred in a variable
degree to the other sex, just
as the pollen-collecting apparatus
of the female has often been
transferred to the male, to whom
it is absolutely useless.*(2)
* "Anwendung der Darwinschen
Lehre auf Bienen," Verh. d. n.
V. Jahrg., xxix.
*(2) M. Perrier,
in his article, "La
Selection sexuelle d'apres Darwin" (Revue
Scientifique, Feb., 1873, p.
868), without apparently having
reflected much on the subject,
objects that as the males of
social bees are known to be produced
from unfertilised ova, they could
not transmit new characters to
their male offspring. This is
an extraordinary objection. A
female bee fertilised by a male,
which presented some character
facilitating the union of the
sexes, or rendering him more
attractive to the female, would
lay eggs which would produce
only females; but these young
females would next year produce
males; and will it be pretended
that such males would not inherit
the characters of their male
grandfathers? To take a case
with ordinary animals as nearly
parallel as possible: if a female
of any white quadruped or bird
were crossed by a male of a black
breed, and the male and female
offspring were paired together,
will it be pretended that the
grandchildren would not inherit
a tendency to blackness from
their male grandfather? The acquirement
of new characters by the sterile
worker-bees is a much more difficult
case, but I have endeavoured
to show in my Origin of Species,
how these sterile beings are
subjected to the power of natural
selection.
Mutilla Europaea makes a stridulating
noise; and according to Goureau*
both sexes have this power. He
attributes the sound to the friction
of the third and preceding abdominal
segments, and I find that these
surfaces are marked with very
fine concentric ridges; but so
is the projecting thoracic collar
into which the head articulates,
and this collar, when scratched
with the point of a needle, emits
the proper sound. It is rather
surprising that both sexes should
have the power of stridulating,
as the male is winged and the
female wingless. It is notorious
that bees express certain emotions,
as of anger, by the tone of their
humming; and according to H.
Muller (p. 80), the males of
some species make a peculiar
singing noise whilst pursuing
the females.
* Quoted by Westwood, Modern
Classification of Insects, vol.
ii., p. 214.
Order: COLEOPTERA (Beetles).-
Many beetles are coloured so
as to resemble the surfaces which
they habitually frequent, and
they thus escape detection by
their enemies. Other species,
for instance diamond-beetles,
are ornamented with splendid
colours, which are often arranged
in stripes, spots, crosses, and
other elegant patterns. Such
colours can hardly serve directly
as a protection, except in the
case of certain flower-feeding
species; but they may serve as
a warning or means of recognition,
on the same principle as the
phosphorescence of the glow-worm.
As with beetles the colours of
the two sexes are generally alike,
we have no evidence that they
have been gained through sexual
selection; but this is at least
possible, for they have been
developed in one sex and then
transferred to the other; and
this view is even in some degree
probable in those groups which
possess other well-marked secondary
sexual characters. Blind beetles,
which cannot of course behold
each other's beauty, never, as
I hear from Mr. Waterhouse, jr.,
exhibit bright colours, though
they often have polished coats;
but the explanation of their
obscurity may be that they generally
inhabit caves and other obscure
stations.
Some longicorns, especially
certain Prionidae, offer an exception
to the rule that the sexes of
beetles do not differ in colour.
Most of these insects are large
and splendidly coloured. The
males in the genus Pyrodes,*
which I saw in Mr. Bates's collection,
are generally redder but rather
duller than the females, the
latter being coloured of a more
or less splendid golden-green.
On the other hand, in one species
the male is golden-green, the
female being richly tinted with
red and purple. In the genus
Esmeralda the sexes differ so
greatly in colour that they have
been ranked as distinct species;
in one species both are of a
beautiful shining green, but
the male has a red thorax. On
the whole, as far as I could
judge, the females of those Prionidae,
in which the sexes differ, are
coloured more richly than the
males, and this does not accord
with the common rule in regard
to colour, when acquired through
sexual selection.
* Pyrodes pulcherrimus, in which
the sexes differ conspicuously,
has been described by Mr. Bates
in Transact. Ent. Soc., 1869,
p. 50. I will specify the few
other cases in which I have heard
of a difference in colour between
the sexes of beetles. Kirby and
Spence (Introduct. to Entomology,
vol. iii., p. 301) mention a
Cantharis, Meloe, Rhagium, and
the Leptura testacea; the male
of the latter being testaceous,
with a black thorax, and the
female of a dull red all over.
These two latter beetles belong
to the family of longicorns.
Messrs. R. Trimen and Waterhouse,
jr., inform me of two lamellicorns,
viz., a Peritrichia and Trichius,
the male of the latter being
more obscurely coloured than
the female. In Tillus elongatus
the male is black, and the female
always, as it is believed, of
a dark blue colour, with a red
thorax. The male, also, of Orsodacna
atra, as I hear from Mr. Walsh,
is black, the female (the so-called
O. ruficollis) having a rufous
thorax.
A most remarkable
distinction between the sexes
of many beetles
is presented by the great horns
which rise from the head, thorax,
and clypeus of the males; and
in some few cases from the under
surface of the body. These horns,
in the great family of the lamellicorns,
resemble those of various quadrupeds,
such as stags, rhinoceroses, &c.,
and are wonderful both from their
size and diversified shapes.
Instead of describing them,
I have given figures of the males
and females of some of the more
remarkable forms. (See Figs.
16 to 20.) The females generally
exhibit rudiments of the horns
in the form of small knobs or
ridges; but some are destitute
of even the slightest rudiment.
On the other hand, the horns
are nearly as well developed
in the female as in the male
Phanaeus lancifer; and only a
little less well developed in
the females of some other species
of this genus and of Copris.
I am informed by Mr. Bates that
the horns do not differ in any
manner corresponding with the
more important characteristic
differences between the several
subdivisions of the family: thus
within the same section of the
genus Onthophagus, there are
species which have a single horn,
and others which have two.
In almost all cases, the horns
are remarkable for their excessive
variability; so that a graduated
series can be formed, from the
most highly developed males to
others so degenerate that they
can barely be distinguished from
the females. Mr. Walsh* found
that in Phanaeus carnifex the
horns were thrice as long in
some males as in others. Mr.
Bates, after examining above
a hundred males of Onthophagus
rangifer (see fig. 20), thought
that he had at last discovered
a species in which the horns
did not vary; but further research
proved the contrary.
* Proceedings of the Entomological
Society of Philadephia, 1864,
p. 228.
The extraordinary size of the
horns, and their widely different
structure in closely-allied forms,
indicate that they have been
formed for some purpose; but
their excessive variability in
the males of the same species
leads to the inference that this
purpose cannot be of a definite
nature. The horns do not show
marks of friction, as if used
for any ordinary work. Some authors
suppose* that as the males wander
about much more than the females,
they require horns as a defence
against their enemies; but as
the horns are often blunt, they
do not seem well adapted for
defence. The most obvious conjecture
is that they are used by the
males for fighting together;
but the males have never been
observed to fight; nor could
Mr. Bates, after a careful examination
of numerous species, find any
sufficient evidence, in their
mutilated or broken condition,
of their having been thus used.
If the males had been habitual
fighters, the size of their bodies
would probably have been increased
through sexual selection, so
as to have exceeded that of the
females; but Mr. Bates, after
comparing the two sexes in above
a hundred species of the Copridae,
did not find any marked difference
in this respect amongst well-developed
individuals. In Lethrus, moreover,
a beetle belonging to the same
great division of the lamellicorns,
the males are known to fight,
but are not provided with horns,
though their mandibles are much
larger than those of the female.
* Kirby and Spence, Introduction
to Entomology, vol. iii., P.
300.
The conclusion that the horns
have been acquired as ornaments
is that which best agrees with
the fact of their having been
so immensely, yet not fixedly,
developed,- as shewn by their
extreme variability in the same
species, and by their extreme
diversity in closely-allied species.
This view will at first appear
extremely improbable; but we
shall hereafter find with many
animals standing much higher
in the scale, namely fishes,
amphibians, reptiles and birds,
that various kinds of crests,
knobs, horns and combs have been
developed apparently for this
sole purpose.
The males of Onitis furcifer
(see fig. 21), and of some other
species of the genus, are furnished
with singular projections on
their anterior femora, and with
a great fork or pair of horns
on the lower surface of the thorax.
Judging from other insects, these
may aid the male in clinging
to the female. Although the males
have not even a trace of a horn
on the upper surface of the body,
yet the females plainly exhibit
a rudiment of a single horn on
the head (see fig. 22, a), and
of a crest (b) on the thorax.
That the slight thoracic crest
in the female is a rudiment of
a projection proper to the male,
though entirely absent in the
male of this particular species,
is clear: for the female of Bubas
bison (a genus which comes next
to Onitis) has a similar slight
crest on the thorax, and the
male bears a great projection
in the same situation. So, again,
there can hardly be a doubt that
the little point (a) on the head
of the female Onitis furcifer,
as well as on the head of the
females of two or three allied
species, is a rudimentary representative
of the cephalic horn, which is
common to the males of so many
lamellicorn beetles, as in Phanaeus
(see fig. 18).
The old belief that rudiments
have been created to complete
the scheme of nature is here
so far from holding good, that
we have a complete inversion
of the ordinary state of things
in the family. We may reasonably
suspect that the males originally
bore horns and transferred them
to the females in a rudimentary
condition, as in so many other
lamellicorns. Why the males subsequently
lost their horns, we know not;
but this may have been caused
through the principle of compensation,
owing to the development of the
large horns and projections on
the lower surface; and as these
are confined to the males, the
rudiments of the upper horns
on the females would not have
been thus obliterated.
The cases hitherto
given refer to the lamellicorns,
but the
males of some few other beetles,
belonging to two widely distinct
groups, namely, the Curculionidae
and Staphylinidae, are furnished
with horns - in the former on
the lower surface of the body,*
in the latter on the upper surface
of the head and thorax. In the
Staphylinidae, the horns of the
males are extraordinarily variable
in the same species, just as
we have seen with the lamellicorns.
In Siagonium we have a case of
dimorphism, for the males can
be divided into two sets, differing
greatly in the size of their
bodies and in the development
of their horns, without intermediate
gradations. In a species of Bledius
(see fig. 23), also belonging
to the Staphylinidae, Professor
Westwood states that, "male specimens
can be found in the same locality
in which the central horn of
the thorax is very large, but
the horns of the head quite rudimental;
and others, in which the thoracic
horn is much shorter, whilst
the protuberances on the head
are long."*(2) Here we apparently
have a case of compensation,
which throws light on that just
given, of the supposed loss of
the upper horns by the males
of Onitis.
* Kirby and Spence, Introduction
to Entomology, vol. iii., p.
329.
*(2) Modern Classification of
Insects, vol. i., p. 172: Siagonium,
p. 172. In the British Museum
I noticed one male specimen of
Siagonium in an intermediate
condition, so that the dimorphism
is not strict.
Law of Battle.-
Some male beetles, which seem
ill-fitted for fighting,
nevertheless engage in conflicts
for the possession of the females.
Mr. Wallace* saw two males of
Leptorhynchus angustatus, a linear
beetle with a much elongated
rostrum, "fighting for a female,
who stood close by busy at her
boring. They pushed at each other
with their rostra, and clawed
and thumped, apparently in the
greatest rage." The smaller male,
however, "soon ran away, acknowledging
himself vanquished." In some
few cases male beetles are well
adapted for fighting, by possessing
great toothed mandibles, much
larger than those of the females.
This is the case with the common
stag-beetle (Lucanus cervus),
the males of which emerge from
the pupal state about a week
before the other sex, so that
several may often be seen pursuing
the same female. At this season
they engage in fierce conflicts.
When Mr. A. H. Davis*(2) enclosed
two males with one female in
a box, the larger male severely
pinched the smaller one, until
he resigned his pretensions.
A friend informs me that when
a boy he often put the males
together to see them fight, and
he noticed that they were much
bolder and fiercer than the females,
as with the higher animals. The
males would seize hold of his
finger, if held in front of them,
but not so the females, although
they have stronger jaws. The
males of many of the Lucanidae
as well as of the above-mentioned
Leptorhynchus, are larger and
more powerful insects than the
females. The two sexes of Lethrus
cephalotes (one of the lamellicorns)
inhabit the same burrow; and
the male has larger mandibles
than the female. If, during the
breeding-season, a strange male
attempts to enter the burrow,
he is attacked; the female does
not remain passive, but closes
the mouth of the burrow, and
encourages her mate by continually
pushing him on from behind; and
the battle lasts until the aggressor
is killed or runs away.*(3) The
two sexes of another lamellicorn
beetle, the Ateuchus cicatricosus,
live in pairs, and seem much
attached to each other; the male
excites the females to roll the
balls of dung in which the ova
are deposited; and if she is
removed, he becomes much agitated.
If the male is removed the female
ceases all work, and as M. Brulerie*(4)
believes, would remain on the
same spot until she died.
* The Malay Archipelago, vol.
ii., 1869, p. 276. Riley, Sixth
Report on Insects of Missouri,
1874, p. 115.
*(2) Entomological Magazine,
vol. i., 1833, p. 82. See also
on the conflicts of this species,
Kirby and Spence, ibid., vol.
iii., p. 314; and Westwood, ibid.,
vol. i., p. 187.
*(3) Quoted from Fischer, in
Dict. Class. d'Hist. Nat., tom.
x., p. 324.
*(4) Ann. Soc. Entomolog. France,
1866, as quoted in Journal of
Travel, by A. Murray, 1868, p.
135.
The great mandibles of the male
Lucanidae are extremely variable
both in size and structure, and
in this respect resemble the
horns on the head and thorax
of many male lamellicorns and
Staphylinidae. A perfect series
can be formed from the best-provided
to the worst-provided or degenerate
males. Although the mandibles
of the common stag-beetle, and
probably of many other species,
are used as efficient weapons
for fighting, it is doubtful
whether their great size can
thus be accounted for. We have
seen that they are used by the
Lucanus elaphus of N. America
for seizing the female. As they
are so conspicuous and so elegantly
branched, and as owing to their
great length they are not well
adapted for pinching, the suspicion
has crossed my mind that they
may in addition serve as an ornament,
like the horns on the head and
thorax of the various species
above described. The male Chiasognathus
grantii of S. Chile- a splendid
beetle belonging to the same
family- has enormously developed
mandibles (see fig. 24); he is
bold and pugnacious; when threatened
he faces round, opens his great
jaws, and at the same time stridulates
loudly. But the mandibles were
not strong enough to pinch my
finger so as to cause actual
pain.
Sexual selection, which implies
the possession of considerable
perceptive powers and of strong
passions, seems to have been
more effective with the lamellicorns
than with any other family of
beetles. With some species the
males are provided with weapons
for fighting; some live in pairs
and show mutual affection; many
have the power of stridulating
when excited; many are furnished
with the most extraordinary horns,
apparently for the sake of ornament;
and some, which are diurnal in
their habits, are gorgeously
coloured. Lastly, several of
the largest beetles in the world
belong to this family, which
was placed by Linnaeus and Fabricius
as the head of the Order.*
* Westwood, Modern Classification,
vol. i., p. 184.
Stridulating organs.- Beetles
belonging to many and widely
distinct families possess these
organs. The sound thus produced
can sometimes be heard at the
distance of several feet or even
yards,* but it is not comparable
with that made by the Orthoptera.
The rasp generally consists of
a narrow, slightly-raised surface,
crossed by very fine, parallel
ribs, sometimes so fine as to
cause iridescent colours, and
having a very elegant appearance
under the microscope. In some
cases, as with Typhoeus, minute,
bristly or scale-like prominences,
with which the whole surrounding
surface is covered in approximately
parallel lines, could be traced
passing into the ribs of the
rasp. The transition takes place
by their becoming confluent and
straight, and at the same time
more prominent and smooth. A
hard ridge on an adjoining part
of the body serves as the scraper
for the rasp, but this scraper
in some cases has been specially
modified for the purpose. It
is rapidly moved across the rasp,
or conversely the rasp across
the scraper.
* Wollaston, "On Certain Musical
Curculionidae," Annals and Mag.
of Nat. Hist., vol. vi., 1860,
p. 14.
These organs
are situated in widely different
positions. In
the carrion-beetles (Necrophorus)
two parallel rasps (see r, fig.
25) stand on the dorsal surface
of the fifth abdominal segment,
each rasp* consisting of 126
to 140 fine ribs. These ribs
are scraped against the posterior
margins of the elytra, a small
portion of which projects beyond
the general outline. In many
Crioceridae, and in Clythra 4-punctata
(one of the Chrysomelidae), and
in some Tenebrionidae, &c.,*(2)
the rasp is seated on the dorsal
apex of the abdomen, on the pygidium
or propygidium, and is scraped
in the same manner by the elytra.
In Heterocerus, which belongs
to another family, the rasps
are placed on the sides of the
first abdominal segment, and
are scraped by ridges on the
femora.*(3) In certain Curculionidae
and Carabidae,*(4) the parts
are completely reversed in position,
for the rasps are seated on the
inferior surface of the elytra,
near their apices, or along their
outer margins, and the edges
of the abdominal segments serve
as the scrapers. In Pelobius
Hermanni (one of Dytiscidae or
water-beetles) a strong ridge
runs parallel and near to the
sutural margin of the elytra,
and is crossed by ribs, coarse
in the middle part, but becoming
gradually finer at both ends,
especially at the upper end;
when this insect is held under
water or in the air, a stridulating
noise is produced by the extreme
horny margin of the abdomen being
scraped against the rasps. In
a great number of longhorned
beetles (Longicornia) the organs
are situated quite otherwise,
the rasp being on the meso-thorax,
which is rubbed against the pro-thorax;
Landois counted 238 very fine
ribs on the rasp of Cerambyx
heros.
* Landois, Zeitschrift fur wissenschaft.
Zoolog., B. xvii., 1867, s. 127.
*(2) I am greatly indebted to
Mr. G. B. Crotch for having sent
me many prepared specimens of
various beetles belonging to
these three families and to others,
as well as for valuable information.
He believes that the power of
stridulation in the Clythra has
not been previously observed.
I am also much indebted to Mr.
E. W. Janson, for information
and specimens. I may add that
my son, Mr. F. Darwin, finds
that Dermestes murinus stridulates,
but he searched in vain for the
apparatus. Scolytus has lately
been described by Dr. Chapman
as a stridulator, in the Entomologist's
Monthly Magazine, vol. vi., p.
130.
*(3) Schiodte, translated, in
Annals and Magazine of Natural
History, vol. xx., 1867, p. 37.
*(4) Westring has described
(Kroyer, Naturhist. Tidskrift,
B. ii., 1848-49, p. 334) the
stridulating organs in these
two, as well as in other families.
In the Carabidae I have examined
Ealphrus uliginosus and Blethisa
multipunctata, sent to me by
Mr. Crotch. In Blethisa the transverse
ridges on the furrowed border
of the abdominal segment do not,
as far as I could judge, come
into play in scraping the rasps
on the elytra.
Many lamellicorns have the power
of stridulating, and the organs
differ greatly in position. Some
species stridulate very loudly,
so that when Mr. F. Smith caught
a Trox sabulosus, a gamekeeper,
who stood by, thought he had
caught a mouse; but I failed
to discover the proper organs
in this beetle. In Geotrupes
and Typhaeus, a narrow ridge
runs obliquely across (see r,
fig. 26) the coxa of each hindleg
(having in G. stercorarius 84
ribs), which is scraped by a
specially projecting part of
one of the abdominal segments.
In the nearly allied Copris lunaris,
an excessively narrow fine rasp
runs along the sutural margin
of the elytra, with another short
rasp near the basal outer margin;
but in some other Coprini the
rasp is seated, according to
Leconte, on the dorsal surface
of the abdomen. In Oryctes it
is seated on the propygidium;
and, according to the same entomologist,
in some other Dynastini, on the
under surface of the elytra.
Lastly, Westring states that
in Omaloplia brunnea the rasp
is placed on the pro-sternum,
and the scraper on the meta-sternum,
the parts thus occupying the
under surface of the body, instead
of the upper surface as in the
Longicorns.
* I am indebted to Mr. Walsh,
of Illinois, for having sent
me extracts from Leconte's Introduction
to Entomology, pp. 101, 143.
We thus see
that in the different coleopterous
families the stridulating
organs are wonderfully diversified
in position, but not much in
structure. Within the same family
some species are provided with
these organs, and others are
destitute of them. This diversity
is intelligible, if we suppose
that originally various beetles
made a shuffling or hissing noise
by the rubbing together of any
hard and rough parts of their
bodies, which happened to be
in contact; and that from the
noise thus produced being in
some way useful, the rough surfaces
were gradually developed into
regular stridulating organs.
Some beetles as they move, now
produce, either intentionally
or unintentionally, a shuffling
noise, without possessing any
proper organs for the purpose.
Mr. Wallace informs me that the
Euchirus longimanus (a lamellicorn,
with the anterior legs wonderfully
elongated in the male) "makes,
whilst moving, a low hissing
sound by the protrusion and contraction
of the abdomen; and when seized
it produces a grating sound by
rubbing its hind-legs against
the edges of the elytra." The
hissing sound is clearly due
to a narrow rasp running along
the sutural margin of each elytron;
and I could likewise make the
grating sound by rubbing the
shagreened surface of the femur
against the granulated margin
of the corresponding elytron;
but I could not here detect any
proper rasp; nor is it likely
that I could have overlooked
it in so large an insect. After
examining Cychrus, and reading
what Westring has written about
this beetle, it seems very doubtful
whether it possesses any true
rasp, though it has the power
of emitting a sound.
From the analogy of the Orthoptera
and Homoptera, I expected to
find the stridulating organs
in the Coleoptera differing according
to sex; but Landois, who has
carefully examined several species,
observed no such difference;
nor did Westring; nor did Mr.
G. R. Crotch in preparing the
many specimens which he had the
kindness to send me. Any difference
in these organs, if slight, would,
however, be difficult to detect,
on account of their great variability.
Thus, in the first pair of specimens
of Necrophorus humator and of
Pelobius which I examined, the
rasp was considerably larger
in the male than in the female;
but not so with succeeding specimens.
In Geotrupes stercorarius the
rasp appeared to me thicker,
opaquer, and more prominent in
three males than in the same
number of females; in order,
therefore, to discover whether
the sexes differed in their power
of stridulating, my son, Mr.
F. Darwin, collected fifty-seven
living specimens, which he separated
into two lots, according as they
made a greater or less noise,
when held in the same manner.
He then examined all these specimens,
and found that the males were
very nearly in the same proportion
to the females in both the lots.
Mr. F. Smith has kept alive numerous
specimens of Monoynchus pseudacori
(Curculionidae), and is convinced
that both sexes stridulate, and
apparently in an equal degree.
Nevertheless, the power of stridulating
is certainly a sexual character
in some few Coleoptera. Mr. Crotch
discovered that the males alone
of two species of Heliopathes
(Tenebrionidae) possess stridulating
organs. I examined five males
of H. gibbus, and in all these
there was a well-developed rasp,
partially divided into two, on
the dorsal surface of the terminal
abdominal segment; whilst in
the same number of females there
was not even a rudiment of the
rasp, the membrane of this segment
being transparent, and much thinner
than in the male. In H. cribratostriatus
the male has a similar rasp,
excepting that it is not partially
divided into two portions, and
the female is completely destitute
of this organ; the male in addition
has on the apical margins of
the elytra, on each side of the
suture, three or four short longitudinal
ridges, which are crossed by
extremely fine ribs, parallel
to and resembling those on the
abdominal rasp; whether these
ridges serve as an independent
rasp, or as a scraper for the
abdominal rasp, I could not decide:
the female exhibits no trace
of this latter structure.
Again, in three species of the
lamellicorn genus Oryctes, we
have a nearly parallel case.
In the females of O. gryphus
and nasicornis the ribs on the
rasp of the pro-pygidium are
less continuous and less distinct
than in the males; but the chief
difference is that the whole
upper surface of this segment,
when held in the proper light,
is seen to be clothed with hairs,
which are absent or are represented
by excessively fine down in the
males. It should be noticed that
in all Coleoptera the effective
part of the rasp is destitute
of hairs. In O. senegalensis
the difference between the sexes
is more strongly marked, and
this is best seen when the proper
abdominal segment is cleaned
and viewed as a transparent object.
In the female the whole surface
is covered with little separate
crests, bearing spines; whilst
in the male these crests in proceeding
towards the apex, become more
and more confluent, regular,
and naked; so that three-fourths
of the segment is covered with
extremely fine parallel ribs,
which are quite absent in the
female. In the females, however,
of all three species of Oryctes,
a slight grating or stridulating
sound is produced, when the abdomen
of a softened specimen is pushed
backwards and forwards.
In the case of the Heliopathes
and Oryctes there can hardly
be a doubt that the males stridulate
in order to call or to excite
the females; but with most beetles
the stridulation apparently serves
both sexes as a mutual call.
Beetles stridulate under various
emotions, in the same manner
as birds use their voices for
many purposes besides singing
to their mates. The great Chiasognathus
stridulates in anger or defiance;
many species do the same from
distress or fear, if held so
that they cannot escape; by striking
the hollow stems of trees in
the Canary Islands, Messrs. Wollaston
and Crotch were able to discover
the presence of beetles belonging
to the genus Acalles by their
stridulation. Lastly, the male
Ateuchus stridulates to encourage
the female in her work, and from
distress when she is removed.*
Some naturalists believe that
beetles make this noise to frighten
away their enemies; but I cannot
think that a quadruped or bird,
able to devour a large beetle,
would be frightened by so slight
a sound. The belief that the
stridulation serves as a sexual
call is supported by the fact
that death-ticks (Anobium tessellatum)
are well known to answer each
other's ticking, and, as I have
myself observed, a tapping noise
artificially made. Mr. Doubleday
also informs me that he has sometimes
observed a female ticking,*(2)
and in an hour or two afterwards
has found her united with a male,
and on one occasion surrounded
by several males. Finally, it
is probable that the two sexes
of many kinds of beetles were
at first enabled to find each
other by the slight shuffling
noise produced by the rubbing
together of the adjoining hard
parts of their bodies; and that
as those males or females which
made the greatest noise succeeded
best in finding partners, rugosities
on various parts of their bodies
were gradually developed by means
of sexual selection into true
stridulating organs.
* M. P. de la Brulerie, as quoted
in Journal of Travel, A. Murray,
vol. i., 1868, p. 135.
*(2) According
to Mr. Doubleday, "the
noise is produced by the insect
raising itself on its legs as
high as it can, and then striking
its thorax five or six times,
in rapid succession, against
the substance upon which it is
sitting." For references on this
subject see Landois, Zeitschrift
fur wissen. Zoolog., B. xvii.,
s. 181. Olivier says (as quoted
by Kirby and Spence, Introduction
to Entomology, vol. ii., p. 395)
that the female of Pimelia striata
produces a rather loud sound
by striking her abdomen against
any hard substance, "and that
the male, obedient to this call,
soon attends her, and they pair." |