IN this great Order the most
interesting points for us are
the differences in colour between
the sexes of the same species,
and between the distinct species
of the same genus. Nearly the
whole of the following chapter
will be devoted to this subject;
but I will first make a few remarks
on one or two other points. Several
males may often be seen pursuing
and crowding round the same female.
Their courtship appears to be
a prolonged affair, for I have
frequently watched one or more
males pirouetting round a female
until I was tired, without seeing
the end of the courtship. Mr.
A. G. Butler also informs me
that he has several times watched
a male courting a female for
a full quarter of an hour; but
she pertinaciously refused him,
and at last settled on the ground
and closed her wings, so as to
escape from his addresses.
Although butterflies
are weak and fragile creatures,
they are
pugnacious, and an emperor butterfly*
has been captured with the tips
of its wings broken from a conflict
with another male. Mr. Collingwood,
in speaking of the frequent battles
between the butterflies of Borneo,
says, "They whirl round each
other with the greatest rapidity,
and appear to be incited by the
greatest ferocity."
* Apatura iris: The Entomologist's
Weekly Intelligence, 1859, p.
139. For the Bornean butterflies,
see C. Collingwood, Rambles of
a Naturalist, 1868, p. 183.
The Ageronia feronia makes a
noise like that produced by a
toothed wheel passing under a
spring catch, and which can be
heard at the distance of several
yards: I noticed this sound at
Rio de Janeiro, only when two
of these butterflies were chasing
each other in an irregular course,
so that it is probably made during
the courtship of the sexes.*
* See my Journal of Researches,
1845, p. 33. Mr. Doubleday has
detected (Proc. Ent. Soc., March
3, 1845, p. 123) a peculiar membranous
sac at the base of the front
wings, which is probably connected
with the production of the sound.
For the case of Thecophora, see
Zoological Record, 1869, p. 401.
For Mr. Buchanan White's observations,
the Scottish Naturalist, July,
1872, p. 214.
Some moths also
produce sounds; for instance,
the males Theocophora
fovea. On two occasions Mr. F.
Buchanan White* heard a sharp
quick noise made by the male
of Hylophila prasinana, and which
he believes to be produced, as
in Cicada, by an elastic membrane,
furnished with a muscle. He quotes,
also, Guenee, that Setina produces
a sound like the ticking of a
watch, apparently by the aid
of "two large tympaniform vesicles,
situated in the pectoral region";
and these "are much more developed
in the male than in the female." Hence
the sound-producing organs in
the Lepidoptera appear to stand
in some relation with the sexual
functions. I have not alluded
to the well-known noise made
by the death's head sphinx, for
it is generally heard soon after
the moth has emerged from its
cocoon.
* The Scottish Naturalist, July,
1872, p. 213.
Giard has always observed that
the musky odour, which is emitted
by two species of sphinx moths,
is peculiar to the males;* and
in the higher classes we shall
meet with many instances of the
males alone being odoriferous.
* Zoological Record, 1869, p.
347.
Every one must
have admired the extreme beauty
of many butterflies
and of some moths; and it may
be asked, are their colours and
diversified patterns the result
of the direct action of the physical
conditions to which these insects
have been exposed, without any
benefit being thus derived? Or
have successive variations been
accumulated and determined as
a protection, or for some unknown
purpose, or that one sex may
be attractive to the other? And,
again, what is the meaning of
the colours being widely different
in the males and females of certain
species, and alike in the two
sexes of other species of the
same genus" Before attempting
to answer these questions a body
of facts must be given.
With our beautiful
English butterflies, the admiral,
peacock, and painted
lady (Vanessae), as well as many
others, the sexes are alike.
This is also the case with the
magnificent Heliconidae, and
most of the Danaidae in the tropics.
But in certain other tropical
groups, and in some of our English
butterflies, as the purple emperor,
orange-tip, &c. (Apatura iris
and Anthocharis cardamines),
the sexes differ either greatly
or slightly in colour. No language
suffices to describe the splendour
of the males of some tropical
species. Even within the same
genus we often find species presenting
extraordinary differences between
the sexes, whilst others have
their sexes closely alike. Thus
in the South American genus Epicalia,
Mr. Bates, to whom I am indebted
for most of the following facts,
and for looking over this whole
discussion, informs me that he
knows twelve species, the two
sexes of which haunt the same
stations (and this is not always
the case with butterflies), and
which, therefore, cannot have
been differently affected by
external conditions.* In nine
of these twelve species the males
rank amongst the most brilliant
of all butterflies, and differ
so greatly from the comparatively
plain females that they were
formerly placed in distinct genera.
The females of these nine species
resemble each other in their
general type of coloration; and
they likewise resemble both sexes
of the species in several allied
genera found in various parts
of the world. Hence we may infer
that these nine species, and
probably all the others of the
genus, are descended from an
ancestral form which was coloured
in nearly the same manner. In
the tenth species the female
still retains the same general
colouring, but the male resembles
her, so that he is coloured in
a much less gaudy and contrasted
manner than the males of the
previous species. In the eleventh
and twelfth species, the females
depart from the usual type, for
they are gaily decorated almost
like the males, but in a somewhat
less degree. Hence in these two
latter species the bright colours
of the males seem to have been
transferred to the females; whilst
in the tenth species the male
has either retained or recovered
the plain colours of the female,
as well as of the parent-form
of the genus. The sexes in these
three cases have thus been rendered
nearly alike, though in an opposite
manner. In the allied genus Eubagis,
both sexes of some of the species
are plain-coloured and nearly
alike; whilst with the greater
number the males are decorated
with beautiful metallic tints
in a diversified manner, and
differ much from their females.
The females throughout the genus
retain the same general style
of colouring, so that they resemble
one another much more closely
than they resemble their own
males.
* See also Mr. Bates's paper
in Proc. Ent. Soc. of Philadelphia,
1865, p. 206. Also Mr. Wallace
on the same subject, in regard
to Diadema, in Transactions,
Entomological Society, London,
1869, p. 278.
In the genus Papilio, all the
species of the Aeneas group are
remarkable for their conspicuous
and strongly contrasted colours,
and they illustrate the frequent
tendency to gradation in the
amount of difference between
the sexes. In a few species,
for instance in P. ascanius,
the males and females are alike;
in others the males are either
a little brighter, or very much
more superb than the females.
The genus Junonia, allied to
our Vanessae, offers a nearly
parallel case, for although the
sexes of most of the species
resemble each other, and are
destitute of rich colours, yet
in certain species, as in J.
oenone, the male is rather more
bright-coloured than the female,
and in a few (for instance J.
andremiaja) the male is so different
from the female that he might
be mistaken for an entirely distinct
species.
Another striking case was pointed
out to me in the British Museum
by Mr. A. Butler, namely, one
of the tropical American Theclae,
in which both sexes are nearly
alike and wonderfully splendid;
in another species the male is
coloured in a similarly gorgeous
manner, whilst the whole upper
surface of the female is of a
dull uniform brown. Our common
little English blue butterflies
of the genus Lycaena, illustrate
the various differences in colour
between the sexes, almost as
well, though not in so striking
a manner, as the above exotic
genera. In Lycaena agestis both
sexes have wings of a brown colour,
bordered with small ocellated
orange spots, and are thus alike.
In L. oegon the wings of the
males are of a fine blue, bordered
with black, whilst those of the
female are brown, with a similar
border, closely resembling the
wings of L. agestis. Lastly,
in L. arion both sexes are of
a blue colour and are very like,
though in the female the edges
of the wings are rather duskier,
with the black spots plainer;
and in a bright blue Indian species
both sexes are still more alike.
I have given the foregoing details
in order to show, in the first
place, that when the sexes of
butterflies differ, the male
as a general rule is the more
beautiful, and departs more from
the usual type of colouring of
the group to which the species
belongs. Hence in most groups
the females of the several species
resemble each other much more
closely than do the males. In
some cases, however, to which
I shall hereafter allude, the
females are coloured more splendidly
than the males. In the second
place, these details have been
given to bring clearly before
the mind that within the same
genus, the two sexes frequently
present every gradation from
no difference in colour, to so
great a difference that it was
long before the two were placed
by entomologists in the same
genus. In the third place, we
have seen that when the sexes
nearly resemble each other, this
appears due either to the male
having transferred his colours
to the female, or to the male
having retained, or perhaps recovered,
the primordial colours of the
group. It also deserves notice
that in those groups in which
the sexes differ, the females
usually somewhat resemble the
males, so that when the males
are beautiful to an extraordinary
degree, the females almost invariably
exhibit some degree of beauty.
From the many cases of gradation
in the amount of difference between
the sexes, and from the prevalence
of the same general type of coloration
throughout the whole of the same
group, we may conclude that the
causes have generally been the
same which have determined the
brilliant colouring of the males
alone of some species, and of
both sexes of other species.
As so many gorgeous butterflies
inhabit the tropics, it has often
been supposed that they owe their
colours to the great heat and
moisture of these zones; but
Mr. Bates* has shown by the comparison
of various closely-allied groups
of insects from the temperate
and tropical regions, that this
view cannot be maintained; and
the evidence becomes conclusive
when brilliantly-coloured males
and plain-coloured females of
the same species inhabit the
same district, feed on the same
food, and follow exactly the
same habits of life. Even when
the sexes resemble each other,
we can hardly believe that their
brilliant and beautifully arranged
colours are the purposeless result
of the nature of the tissues
and of the action of the surrounding
conditions.
* The Naturalist on the Amazons,
vol. i., 1863, p. 19.
With animals of all kinds, whenever
colour has been modified for
some special purpose, this has
been, as far as we can judge,
either for direct or indirect
protection, or as an attraction
between the sexes. With many
species of butterflies the upper
surfaces of the wings are obscure;
and this in all probability leads
to their escaping observation
and danger. But butterflies would
be particularly liable to be
attacked by their enemies when
at rest; and most kinds whilst
resting raise their wings vertically
over their backs, so that the
lower surface alone is exposed
to view. Hence it is this side
which is often coloured so as
to imitate the objects on which
these insects commonly rest.
Dr. Rossler, I believe, first
noticed the similarity of the
closed wings of certain Vanessae
and other butterflies to the
bark of trees. Many analogous
and striking facts could be given.
The most interesting one is that
recorded by Mr. Wallace* of a
common Indian and Sumatran butterfly
(Kallima) which disappears like
magic when it settles on a bush;
for it hides its head and antennae
between its closed wings, which,
in form, colour and veining,
cannot be distinguished from
a withered leaf with its footstalk.
In some other cases the lower
surfaces of the wings are brilliantly
coloured, and yet are protective;
thus in Thecla rubi the wings
when closed are of an emerald
green, and resemble the young
leaves of the bramble, on which
in spring this butterfly may
often be seen seated. It is also
remarkable that in very many
species in which the sexes differ
greatly in colour on their upper
surface, the lower surface is
closely similar or identical
in both sexes, and serves as
a protection.*(2)
* See the interesting article
in the Westminster Review, July,
1867, p. 10. A woodcut of the
Kallima is given by Mr. Wallace
in Hardwicke's Science Gossip,
September 1867, p. 196.
*(2) Mr. G. Fraser, in Nature,
April, 1871, p. 489.
Although the obscure tints both
of the upper and under sides
of many butterflies no doubt
serve to conceal them, yet we
cannot extend this view to the
brilliant and conspicuous colours
on the upper surface of such
species as our admiral and peacock
Vanessae, our white cabbage-butterflies
(Pieris), or the great swallowtail
Papilio which haunts the open
fens- for these butterflies are
thus rendered visible to every
living creature. In these species
both sexes are alike; but in
the common brimstone butterfly
(Gonepteryx rhamni), the male
is of an intense yellow, whilst
the female is much paler; and
in the orange-tip (Anthocharis
cardamines) the males alone have
their wings tipped with bright
orange. Both the males and females
in these cases are conspicuous,
and it is not credible that their
difference in colour should stand
in any relation to ordinary protection.
Prof. Weismann remarks,* that
the female of one of the Lycaenae
expands her brow wings when she
settles on the ground, and is
then almost invisible; the male,
on the other hand, as if aware
of the danger incurred from the
bright blue of the upper surface
of his wings, rests with them
closed; and this shows that the
blue colour cannot be in any
way protective. Nevertheless,
it is probable that conspicuous
colours are indirectly beneficial
to many species, as a warning
that they are unpalatable. For
in certain other cases, beauty
has been gained through the imitation
of other beautiful species, which
inhabit the same district and
enjoy an immunity from attack
by being in some way offensive
to their enemies; but then we
have to account for the beauty
of the imitated species.
* Einfluss der Isolirung auf
die Artbildung, 1872, p. 58.
As Mr. Walsh has remarked to
me, the females of our orange-tip
butterfly, above referred to,
and of an American species (Anth.
genutia) probably show us the
primordial colours of the parent-species
of the genus; for both sexes
of four or five widely-distributed
species are coloured in nearly
the same manner. As in several
previous cases, we may here infer
that it is the males of Anth.
cardamines and genutia which
have departed from the usual
type of the genus. In the Anth.
sara from California, the orange-tips
to the wings have been partially
developed in the female; but
they are paler than in the male,
and slightly different in some
other respects. In an allied
Indian form, the Iphias glaucippe,
the orange-tips are fully developed
in both sexes. In this Iphias,
as pointed out to me by Mr. A.
Butler, the under surface of
the wings marvellously resembles
a pale-coloured leaf; and in
our English orange-tip, the under
surface resembles the flower-head
of the wild parsley, on which
the butterfly often rests at
night.* The same reason which
compels us to believe that the
lower surfaces have here been
coloured for the sake of protection,
leads us to deny that the wings
have been tipped with bright
orange for the same purpose,
especially when this character
is confined to the males.
* See the interesting observations
by T. W. Wood, the Student, Sept.,
1868, p. 81.
Most moths rest
motionless during the whole
or greater part of
the day with their wings depressed;
and the whole upper surface shaded
and coloured in an admirable
manner, as Mr. Wallace has remarked,
for escaping detection. The front-wings
of the Bombycidae,* when at rest,
generally overlap and conceal
the hind-wings; so that the latter
might be brightly coloured without
much risk; and they are in fact
often thus coloured. During flight,
moths would often be able to
escape from their enemies; nevertheless,
as the hind-wings are then fully
exposed to view, their bright
must generally have been acquired
at some little risk. But the
following fact shews how cautious
we ought to be in drawing conclusions
on this head. The common yellow
under-wings (Triphoena) often
fly about during the day or early
evening, and are then conspicuous
from the colour of their hind-wings.
It would naturally be thought
that this would be a source of
danger; but Mr. J. Jenner Weir
believes that it actually serves
them as a means of escape, for
birds strike at these brightly
coloured and fragile surfaces,
instead of at the body. For instance,
Mr. Weir turned into his aviary
a vigorous specimen of Triphoena
pronuba, which was instantly
pursued by a robin; but the bird's
attention being caught by the
coloured wings, the moth was
not captured until after about
fifty attempts, and small portions
of the wings were repeatedly
broken off. He tried the same
experiment, in the open air,
with a swallow and T. fimbria;
but the large size of this moth
probably interfered with its
capture.*(2) We are thus reminded
of a statement made by Mr. Wallace,*(3)
namely, that in the Brazilian
forests and Malayan islands,
many common and highly-decorated
butterflies are weak flyers,
though furnished with a broad
expanse of wing; and they "are
often captured with pierced and
broken wings, as if they had
been seized by birds, from which
they had escaped: if the wings
had been much smaller in proportion
to the body, it seems probable
that the insect would more frequently
have been struck or pierced in
a vital part, and thus the increased
expanse of the wings may have
been indirectly beneficial."
* Mr. Wallace in Harwicke's
Science Gossip, September, 1867,
p. 193.
*(2) See also, on this subject,
Mr. Weir's paper in Transactions,
Entomological Society, 1869,
p. 23.
*(3) Westminster Review, July,
1867, p. 16.
Display.- The bright colours
of many butterflies and of some
moths are specially arranged
for display, so that they may
be readily seen. During the night
colours are not visible, and
there can be no doubt that the
nocturnal moths, taken as a body,
are much less gaily decorated
than butterflies, all of which
are diurnal in their habits.
But the moths of certain families,
such as the Zygaenidae, several
Sphingidae, Uraniidae, some Arctiidae
and Saturniidae, fly about during
the day or early evening, and
many of these are extremely beautiful,
being far brighter coloured than
the strictly nocturnal kinds.
A few exceptional cases, however,
of bright-coloured nocturnal
species have been recorded.*
* For instance, Lithosia; but
Prof. Westwood (Modern Class.
of Insects, vol. ii., p. 390)
seems surprised at this case.
On the relative colours of diurnal
and nocturnal Lepidoptera, see
ibid., pp. 333 and 392; also
Harris, Treatise on the Insects
of New England, 1842, p. 315.
There is evidence of another
kind in regard to display. Butterflies,
as before remarked, elevate their
wings when at rest, but whilst
basking in the sunshine often
alternately raise and depress
them, thus exposing both surfaces
to full view; and although the
lower surface is often coloured
in an obscure manner as a protection,
yet in many species it is as
highly decorated as the upper
surface, and sometimes in a very
different manner. In some tropical
species the lower surface is
even more brilliantly coloured
than the upper.* In the English
fritillaries (Argynnis) the lower
surface alone is ornamented with
shining silver. Nevertheless,
as a general rule, the upper
surface, which is probably more
fully exposed, is coloured more
brightly and diversely than the
lower. Hence the lower surface
generally affords to entomologists
the more useful character for
detecting the affinities of the
various species. Fritz Muller
informs me that three species
of Castnia are found near his
house in S. Brazil: of two of
them the hind-wings are obscure,
and are always covered by the
front-wings when these butterflies
are at rest; but the third species
has black hind-wings, beautifully
spotted with red and white, and
these are fully expanded and
displayed whenever the butterfly
rests. Other such cases could
be added.
* Such differences
between the upper and lower
surfaces of the
wings of several species of Papilio
may be seen in the beautiful
plates to Mr. Wallace's "Memoir
on the Papilionidae of the Malayan
Region," in Transactions of the
Linnean Society, vol. xxv., part
i., 1865.
If we now turn
to the enormous group of moths,
which, as I hear
from Mr. Stainton, do not habitually
expose the under surface of their
wings to full view, we find this
side very rarely coloured with
a brightness greater than, or
even equal to, that of the upper
side. Some exceptions to the
rule, either real or apparent,
must be noticed, as the case
of Hypopyra.* Mr. Trimen informs
me that in Guenee's great work,
three moths are figured, in which
the under surface is much the
more brilliant. For instance,
in the Australian Gastrophora
the upper surface of the fore
-wing is pale greyish-ochreous,
while the lower surface is magnificently
ornamented by an ocellus of cobalt-blue,
placed in the midst of a black
mark, surrounded by orange-yellow,
and this by bluish-white. But
the habits of these three moths
are unknown; so that no explanation
can be given of their unusual
style of colouring. Mr. Trimen
also informs me that the lower
surface of the wings in certain
other Geometrae*(2) and quadrifid
Noctuae are either more variegated
or more brightly-coloured than
the upper surface; but some of
these species have the habit
of "holding their wings quite
erect over their backs, retaining
them in this position for a considerable
time," and thus exposing the
under surface to view. Other
species, when settled on the
ground or herbage, now and then
suddenly and slightly lift up
their wings. Hence the lower
surface of the wings being brighter
than the upper surface in certain
moths is not so anomalous as
it at first appears. The Saturniidae
include some of the most beautiful
of all moths, their wings being
decorated, as in our British
emperor moth, with fine ocelli;
and Mr. T. W. Wood*(3) observes
that they resemble butterflies
in some of their movements; "for
instance, in the gentle waving
up and down of the wings as if
for display, which is more characteristic
of diurnal than of nocturnal
Lepidoptera."
* See Mr. Wormald on this moth:
Proceedings of the Entomological
Society, March 2, 1868.
*(2) See also an account of
the S. American genus Erateina
(one of the Geometrae) in Transactions,
Ent., Soc., new series, vol.
v., pls. xv. and xvi.
*(3) Proc Ent. Soc. of London,
July 6, 1868, p. xxvii.
It is a singular fact that no
British moths which are brilliantly
coloured, and, as far as I can
discover, hardly any foreign
species, differ much in colour
according to sex; though this
is the case with many brilliant
butterflies. The male, however,
of one American moth, the Saturnia
io, is described as having its
forewings deep yellow, curiously
marked with purplish-red spots;
whilst the wings of the female
are purple-brown, marked with
grey lines.* The British moths
which differ sexually in colour
are all brown, or of various
dull yellow tints, or nearly
white. In several species the
males are much darker than the
females,*(2) and these belong
to groups which generally fly
about during the afternoon. On
the other hand, in many genera,
as Mr. Stainton informs me, the
males have the hind-wings whiter
than those of the female- of
which fact Agrotis exclamationis
offers a good instance. In the
ghost-moth (Hepialus humuli)
the difference is more strongly
marked; the males being white,
and the females yellow with darker
markings.*(3) It is probable
that in these cases the males
are thus rendered more conspicuous,
and more easily seen by the females
whilst flying about in the dusk.
* Harris, Treatise, &c.,
edited by Flint, 1862, p. 395.
*(2) For instance, I observe
in my son's cabinet that the
males are darker than the females
in the Lasiocampa quercus Odonestis
potatoria, Hypogymna dispar,
Dasychira pudibunda, and Cycnia
mendica. In this latter species
the difference in colour between
the two sexes is strongly marked;
and Mr. Wallace informs me that
we here have, as he believes,
an instance of protective mimicry
confined to one sex, as will
hereafter be more fully explained.
The white female of the Cycnia
resembles the very common Spilosoma
menthrasti, both sexes of which
are white; and Mr. Stainton observed
that this latter moth was rejected
with utter disgust by a whole
brood of young turkeys, which
were fond of eating other moths;
so that if the Cycnia was commonly
mistaken by British birds for
the Spilosoma, it would escape
being devoured, and its white
deceptive colour would thus be
highly beneficial.
*(3) It is remarkable, that
in the Shetland Islands the male
of this moth, instead of differing
widely from the female, frequently
resembles her closely in colour
(see Mr. MacLachlan, Transactions,
Entomological Society, vol. ii.,
1866, p. 459). Mr. G. Fraser
suggests (Nature, April, 1871,
p. 489) that at the season of
the year when the ghost-moth
appears in these northern islands,
the whiteness of the males would
not be needed to render them
visible to the females in the
twilight night.
From the several
foregoing facts it is impossible
to admit that
the brilliant colours of butterflies,
and of some few moths, have commonly
been acquired for the sake of
protection. We have seen that
their colours and elegant patterns
are arranged and exhibited as
if for display. Hence I am led
to believe that the females prefer
or are most excited by the more
brilliant males; for on any other
supposition the males would,
as far as we can see, be ornamented
to no purpose. We know that ants
and certain lamellicorn beetles
are capable of feeling an attachment
for each other, and that ants
recognise their fellows after
an interval of several months.
Hence there is no abstract improbability
in the Lepidoptera, which probably
stand nearly or quite as high
in the scale as these insects,
having sufficient mental capacity
to admire bright colours. They
certainly discover flowers by
colour. The humming-bird sphinx
may often be seen to swoop down
from a distance on a bunch of
flowers in the midst of green
foliage; and I have been assured
by two persons abroad, that these
moths repeatedly visit flowers
painted on the walls of a room,
and vainly endeavour to insert
their proboscis into them. Fritz
Muller informs me that several
kinds of butterflies in S. Brazil
shew an unmistakable preference
for certain colours over others:
he observed that they very often
visited the brilliant red flowers
of five or six genera of plants,
but never the white or yellow
flowering species of the same
and other genera, growing in
the same garden; and I have received
other accounts to the same effect.
As I hear from Mr. Doubleday,
the common white butterfly often
flies down to a bit of paper
on the ground, no doubt mistaking
it for one of its own species.
Mr. Collingwood* in speaking
of the difficulty in collecting
certain butterflies in the Malay
Archipelago, states that "a dead
specimen pinned upon a conspicuous
twig will often arrest an insect
of the same species in its headlong
flight, and bring it down within
easy reach of the net, especially
if it be of the opposite sex."
* Rambles of a Naturalist in
the Chinese Seas, 1868, p. 182.
The courtship of butterflies
is, as before remarked, a prolonged
affair. The males sometimes fight
together in rivalry; and many
may be seen pursuing or crowding
round the same female. Unless,
then, the females prefer one
male to another, the pairing
must be left to mere chance,
and this does not appear probable.
If, on the other band, the females
habitually, or even occasionally,
prefer the more beautiful males,
the colours of the latter will
have been rendered brighter by
degrees, and will have been transmitted
to both sexes or to one sex,
according to the law of inheritance
which has prevailed. The process
of sexual selection will have
been much facilitated, if the
conclusion can be trusted, arrived
at from various kinds of evidence
in the supplement to the ninth
chapter; namely, that the males
of many Lepidoptera, at least
in the imago state, greatly exceed
the females in number.
Some facts, however, are opposed
to the belief that female butterflies
prefer the more beautiful males;
thus, as I have been assured
by several collectors, fresh
females may frequently be seen
paired with battered, faded,
or dingy males; but this is a
circumstance which could hardly
fail often to follow from the
males emerging from their cocoons
earlier than the females. With
moths of the family of the Bombycidae,
the sexes pair immediately after
assuming the imago state; for
they cannot feed, owing to the
rudimentary condition of their
mouths. The females, as several
entomologists have remarked to
me, lie in an almost torpid state,
and appear not to evince the
least choice in regard to their
partners. This is the case with
the common silk-moth (B. mori),
as I have been told by some continental
and English breeders. Dr. Wallace,
who has had great experience
in breeding Bombyx cynthia, is
convinced that the females evince
no choice or preference. He has
kept above 300 of these moths
together, and has often found
the most vigorous females mated
with stunted males. The reverse
appears to occur seldom; for,
as he believes, the more vigorous
males pass over the weakly females,
and are attracted by those endowed
with most vitality. Nevertheless,
the Bombycidae, though obscurely-coloured,
are often beautiful to our eyes
from their elegant and mottled
shades.
I have as yet only referred
to the species in which the males
are brighter coloured than the
females, and I have attributed
their beauty to the females for
many generations having chosen
and paired with the more attractive
males. But converse cases occur,
though rarely, in which the females
are more brilliant than the males;
and here, as I believe, the males
have selected the more beautiful
females, and have thus slowly
added to their beauty. We do
not know why in various classes
of animals the males of some
few species have selected the
more beautiful females instead
of having gladly accepted any
female, as seems to be the general
rule in the animal kingdom: but
if, contrary to what generally
occurs with the Lepidoptera,
the females were much more numerous
than the males, the latter would
be likely to pick out the more
beautiful females. Mr. Butler
shewed me several species of
Callidryas in the British Museum,
in some of which the females
equalled, and in others greatly
surpassed the males in beauty;
for the females alone have the
borders of their wings suffused
with crimson and orange, and
spotted with black. The plainer
males of these species closely
resemble each other, shewing
that here the females have been
modified; whereas in those cases,
where the males are the more
ornate, it is these which have
been modified, the females remaining
closely alike.
In England we
have some analogous cases,
though not so marked.
The females alone of two species
of Thecla have a bright-purple
or orange patch on their fore-wings.
In Hipparchia the sexes do not
differ much; but it is the female
of H. janira which has a conspicuous
light-brown patch on her wings;
and the females of some of the
other species are brighter coloured
than their males. Again, the
females of Colias edusa and hyale
have "orange or yellow spots
on the black marginal border,
represented in the males only
by thin streaks"; and in Pieris
it is the females which "are
ornamented with black spots on
the fore-wings, and these are
only partially present in the
males." Now the males of many
butterflies are known to support
the females during their marriage
flight; but in the species just
named it is the females which
support the males; so that the
part which the two sexes play
is reversed, as is their relative
beauty. Throughout the animal
kingdom the males commonly take
the more active share in wooing,
and their beauty seems to have
been increased by the females
having accepted the more attractive
individuals; but with these butterflies,
the females take the more active
part in the final marriage ceremony,
so that we may suppose that they
likewise do so in the wooing;
and in this case we can understand
how it is that they have been
rendered the more beautiful.
Mr. Meldola, from whom the foregoing
statements have been taken, says
in conclusion: "Though I am not
convinced of the action of sexual
selection in producing the colours
of insects, it cannot be denied
that these facts are strikingly
corroborative of Mr. Darwin's
views."*
* Nature, April 27, 1871, p.
508. Mr. Meldola quotes Donzel,
in Soc. Ent. de France, 1837,
p. 77, on the flight of butterflies
whilst pairing. See also Mr.
G. Fraser, in Nature, April 20,
1871, p. 489, on the sexual differences
of several British butterflies.
As sexual selection primarily
depends on variability, a few
words must be added on this subject.
In respect to colour there is
no difficulty, for any number
of highly variable Lepidoptera
could be named. One good instance
will suffice. Mr. Bates shewed
me a whole series of specimens
of Papilio sesostris and P. childrenae;
in the latter the males varied
much in the extent of the beautifully
enamelled green patch on the
fore-wings, and in the size of
the white mark, and of the splendid
crimson stripe on the hind-wings;
so that there was a great contrast
amongst the males between the
most and the least gaudy. The
male of Papilio sesostris is
much less beautiful than of P.
childrenae; and it likewise varies
a little in the size of the green
patch on the fore-wings, and
in the occasional appearance
of the small crimson stripe on
the hind-wings, borrowed, as
it would seem, from its own female;
for the females of this and of
many other species in the Aeneas
group possess this crimson stripe.
Hence between the brightest specimens
of P. sesostris and the dullest
of P. childrenae, there was but
a small interval; and it was
evident that as far as mere variability
is concerned, there would be
no difficulty in permanently
increasing the beauty of either
species by means of selection.
The variability is here almost
confined to the male sex; but
Mr. Wallace and Mr. Bates have
shewn* that the females of some
species are extremely variable,
the males being nearly constant.
In a future chapter I shall have
occasion to shew that the beautiful
eye-like spots, or ocelli, found
on the wings of many Lepidoptera,
are eminently variable. I may
here add that these ocelli offer
a difficulty on the theory of
sexual selection; for though
appearing to us so ornamental,
they are never present in one
sex and absent in the other,
nor do they ever differ much
in the two sexes.*(2) This fact
is at present inexplicable; but
if it should hereafter be found
that the formation of an ocellus
is due to some change in the
tissues of the wings, for instance,
occurring at a very early period
of development, we might expect,
from what we know of the laws
of inheritance, that it would
be transmitted to both sexes,
though arising and perfected
in one sex alone.
* Wallace on
the "Papilionidae
of the Malayan Region," in Transact.
Linn. Soc., vol. xxv., 1865,
pp. 8, 36. A striking case of
a rare variety, strictly intermediate
between two other well-marked
female varieties, is given by
Mr. Wallace. See also Mr. Bates,
in Proc. Entomolog. Soc., Nov.
19, 1866, p. xl.
*(2) Mr. Bates was so kind as
to lay this subject before the
Entomological Society, and I
have received answers to this
effect from several entomologists.
On the whole, although many
serious objections may be urged,
it seems probable that most of
the brilliantly-coloured species
of Lepidoptera owe their colours
to sexual selection, excepting
in certain cases, presently to
be mentioned, in which conspicuous
colours have been gained through
mimicry as a protection. From
the ardour of the male throughout
the animal kingdom, he is generally
willing to accept any female;
and it is the female which usually
exerts a choice. Hence, if sexual
selection has been efficient
with the Lepidoptera, the male,
when the sexes differ, ought
to be the more brilliantly coloured,
and this undoubtedly is the case.
When both sexes are brilliantly
coloured and resemble each other,
the characters acquired by the
males appear to have been transmitted
to both. We are led to this conclusion
by cases, even within the same
genus, of gradation from an extraordinary
amount of difference to identity
in colour between the two sexes.
But it may be asked whether
the difference in colour between
the sexes may not be accounted
for by other means besides sexual
selection. Thus the males and
females of the same species of
butterfly are in several cases
known* to inhabit different stations,
the former commonly basking in
the sunshine, the latter haunting
gloomy forests. It is therefore
possible that different conditions
of life may have acted directly
on the two sexes; but this is
not probable*(2) as in the adult
state they are exposed to different
conditions during a very short
period; and the larvae of both
are exposed to the same conditions.
Mr. Wallace believes that the
difference between the sexes
is due not so much to the males
having been modified, as to the
females having in all or almost
all cases acquired dull colours
for the sake of protection. It
seems to me, on the contrary,
far more probable that it is
the males which have been chiefly
modified through sexual selection,
the females having been comparatively
little changed. We can thus understand
how it is that the females of
allied species generally resemble
one another so much more closely
than do the males. They thus
shew us approximately the primordial
colouring of the parent-species
of the group to which they belong.
They have, however, almost always
been somewhat modified by the
transfer to them of some of the
successive variations, through
the accumulation of which the
males were rendered beautiful.
But I do not wish to deny that
the females alone of some species
may have been specially modified
for protection. In most cases
the males and females of distinct
species will have been exposed
during their prolonged larval
state to different conditions,
and may have been thus affected;
though with the males any slight
change of colour thus caused
will generally have been masked
by the brilliant tints gained
through sexual selection. When
we treat of birds, I shall have
to discuss the whole question,
as to how far the differences
in colour between the sexes are
due to the males having been
modified through sexual selection
for ornamental purposes, or to
the females having been modified
through natural selection for
the sake of protection, so that
I will here say but little on
the subject.
* H. W. Bates, The Naturalist
on the Amazons, vol. ii., 1863,
p. 228. A. R. Wallace, in Transactions,
Linnean Society, vol. xxv., 1865,
p. 10.
*(2) On this whole subject see
The Variation of Animals and
Plants under Domestication, 1868,
vol. ii., chap. xxiii.
In all the cases in which the
more common form of equal inheritance
by both sexes has prevailed,
the selection of bright-coloured
males would tend to make the
females bright-coloured; and
the selection of dull-coloured
females would tend to make the
males dull. If both processes
were carried on simultaneously,
they would tend to counteract
each other; and the final result
would depend on whether a greater
number of females from being
well protected by obscure colours,
or a greater number of males
by being brightly-coloured and
thus finding partners, succeeded
in leaving more numerous offspring.
In order to account for the
frequent transmission of characters
to one sex alone, Mr. Wallace
expresses his belief that the
more common form of equal inheritance
by both sexes can be changed
through natural selection into
inheritance by one sex alone,
but in favour of this view I
can discover no evidence. We
know from what occurs under domestication
that new characters often appear,
which from the first are transmitted
to one sex alone; and by the
selection of such variations
there would not be the slightest
difficulty in giving bright colours
to the males alone, and at the
same time or subsequently, dull
colours to the females alone.
In this manner the females of
some butterflies and moths have,
it is probable, been rendered
inconspicuous for the sake of
protection, and widely different
from their males.
I am, however, unwilling without
distinct evidence to admit that
two complex processes of selection,
each requiring the transference
of new characters to one sex
alone, have been carried on with
a multitude of species,- that
the males have been rendered
more brilliant by beating their
rivals, and the females more
dull-coloured by having escaped
from their enemies. The male,
for instance, of the common brimstone
butterfly (Gonepteryx), is of
a far more intense yellow than
the female, though she is equally
conspicuous; and it does not
seem probable that she specially
acquired her pale tints as a
protection, though it is probable
that the male acquired his bright
colours as a sexual attraction.
The female of Anthocharis cardamines
does not possess the beautiful
orange wing-tips of the male;
consequently she closely resembles
the white butterflies (Pieris)
so common in our gardens; but
we have no evidence that this
resemblance is beneficial to
her. As, on the other hand, she
resembles both sexes of several
other species of the genus inhabiting
various quarters of the world,
it is probable that she has simply
retained to a large extent her
primordial colours.
Finally, as we have seen, various
considerations lead to the conclusion
that with the greater number
of brilliantly-coloured Lepidoptera
it is the male which has been
chiefly modified through sexual
selection; the amount of difference
between the sexes mostly depending
on the form of inheritance which
has prevailed. Inheritance is
govemed by so many unknown laws
or conditions, that it seems
to us to act in a capricious
manner;* and we can thus, to
a certain extent, understand
how it is that with closely allied
species the sexes either differ
to an astonishing degree, or
are identical in colour. As all
the successive steps in the process
of variation are necessarily
transmitted through the female,
a greater or less number of such
steps might readily become developed
in her; and thus we can understand
the frequent gradations from
an extreme difference to none
at all between the sexes of allied
species. These cases of gradation,
it may be added, are much too
common to favour the supposition
that we here see females actually
undergoing the process of transition
and losing their brightness for
the sake of protection; for we
have every reason to conclude
that at any one time the greater
number of species are in a fixed
condition.
* The Variation of Animals and
Plants under Domestication, vol.
ii., chap. xii., p. 17.
Mimicry.- This principle was
first made clear in an admirable
paper by Mr. Bates,* who thus
threw a flood of light on many
obscure problems. It had previously
been observed that certain butterflies
in S. America belonging to quite
distinct families, resembled
the Heliconidae so closely in
every stripe and shade of colour,
that they could not be distinguished
save by an experienced entomologist.
As the Heliconidae are coloured
in their usual manner, whilst
the others depart from the usual
colouring of the groups to which
they belong, it is clear that
the latter are the imitators,
and the Heliconidae the imitated.
Mr. Bates further observed that
the imitating species are comparatively
rare, whilst the imitated abound,
and that the two sets live mingled
together. From the fact of the
Heliconidae being conspicuous
and beautiful insects, yet so
numerous in individuals and species,
he concluded that they must be
protected from the attacks of
enemies by some secretion or
odour; and this conclusion has
now been amply confirmed,*(2)
especially by Mr. Belt. Hence
Mr. Bates inferred that the butterflies
which imitate the protected species
have acquired their present marvellously
deceptive appearance through
variation and natural selection,
in order to be mistaken for the
protected kinds, and thus to
escape being devoured. No explanation
is here attempted of the brilliant
colours of the imitated, but
only of the imitating butterflies.
We must account for the colours
of the former in the same general
manner, as in the cases previously
discussed in this chapter. Since
the publication of Mr. Bates's
paper, similar and equally striking
facts have been observed by Mr.
Wallace in the Malayan region,
by Mr. Trimen in South Africa,
and by Mr. Riley in the United
States.*(3)
* Transact. Linn. Soc., vol.
xxiii., 1862, p. 495.
*(2) Proc. Entomological Soc.,
Dec. 3, 1866, p. xlv.
*(3) Wallace, Transact. Linn.
Soc., vol. xxv., 1865 p. i.;
also, Transact. Ent. Soc., vol.
iv., 3rd series: 1867, p. 301.
Trimen, Linn. Transact., vol.
xxvi., 1869, p. 497. Riley, Third
Annual Report on the Noxious
Insects of Missouri, 1871, pp.
163-168. This latter essay is
valuable, as Mr. Riley here discusses
all the objections which have
been raised against Mr. Bates's
theory.
As some writers have felt much
difficulty in understanding how
the first steps in the process
of mimicry could have been effected
through natural selection, it
may be well to remark that the
process probably commenced long
ago between forms not widely
dissimilar in colour. In this
case even a slight variation
would be beneficial, if it rendered
the one species more like the
other; and afterwards the imitated
species might be modified to
an extreme degree through sexual
selection or other means, and
if the changes were gradual,
the imitators might easily be
led along the same track, until
they differed to an equally extreme
degree from their original condition;
and they would thus ultimately
assume an appearance or colouring
wholly unlike that of the other
members of the group to which
they belonged. It should also
be remembered that many species
of Lepidoptera are liable to
considerable and abrupt variations
in colour. A few instances have
been given in this chapter; and
many more may be found in the
papers of Mr. Bates and Mr. Wallace.
With several
species the sexes are alike,
and imitate the two
sexes of another species. But
Mr. Trimen gives, in the paper
already referred to, three cases
in which the sexes of the imitated
form differ from each other in
colour, and the sexes of the
imitating form differ in a like
manner. Several cases have also
been recorded where the females
alone imitate brilliantly-coloured
and protected species, the males
retaining "the normal aspect
of their immediate congeners." It
is here obvious that the successive
variations by which the female
has been modified have been transmitted
to her alone. It is, however,
probable that some of the many
successive variations would have
been transmitted to, and developed
in, the males had not such males
been eliminated by being thus
rendered less attractive to the
females; so that only those variations
were preserved which were from
the first strictly limited in
their transmission to the female
sex. We have a partial illustration
of these remarks in a statement
by Mr. Belt;* that the males
of some of the Leptalides, which
imitate protected species, still
retain in a concealed manner
some of their original characters.
Thus in the males "the upper
half of the lower wing is of
a pure white, whilst all the
rest of the wings is barred and
spotted with black, red and yellow,
like the species they mimic.
The females have not this white
patch, and the males usually
conceal it by covering it with
the upper wing, so that I cannot
imagine its being of any other
use to them than as an attraction
in courtship, when they exhibit
it to the females, and thus gratify
their deep-seated preference
for the normal colour of the
Order to which the Leptalides
belong."
* The Naturalist in Nicaragua,
1874, p. 385.
Bright Colours of Caterpillars.-
Whilst reflecting on the beauty
of many butterflies, it occurred
to me that some caterpillars
were splendidly coloured; and
as sexual selection could not
possibly have here acted, it
appeared rash to attribute the
beauty of the mature insect to
this agency, unless the bright
colours of their larvae could
be somehow explained. In the
first place, it may be observed
that the colours of caterpillars
do not stand in any close correlation
with those of the mature insect.
Secondly, their bright colours
do not serve in any ordinary
manner as a protection. Mr. Bates
informs me, as an instance of
this, that the most conspicuous
caterpillar which he ever beheld
(that of a sphinx) lived on the
large green leaves of a tree
on the open llanos of South America;
it was about four inches in length,
transversely banded with black
and yellow, and with its head,
legs, and tail of a bright red.
Hence it caught the eye of any
one who passed by, even at the
distance of many yards, and no
doubt that of every passing bird.
I then applied
to Mr. Wallace, who has an
innate genius for
solving difficulties. After some
consideration he replied: "Most
caterpillars require protection,
as may be inferred from some
kinds being furnished with spines
or irritating hairs, and from
many being coloured green like
the leaves on which they feed,
or being curiously like the twigs
of the trees on which they live." Another
instance of protection, furnished
me by Mr. J. Mansel Weale, may
be added, namely, that there
is a caterpillar of a moth which
lives on the mimosas in South
Africa, and fabricates for itself
a case quite indistinguishable
from the surrounding thorns.
From such considerations Mr.
Wallace thought it probable that
conspicuously coloured caterpillars
were protected by having a nauseous
taste; but as their skin is extremely
tender, and as their intestines
readily protrude from a wound,
a slight peck from the beak of
a bird would be as fatal to them
as if they had been devoured.
Hence, as Mr. Wallace remarks, "distastefulness
alone would be insufficient to
protect a caterpillar unless
some outward sign indicated to
its would-be destroyer that its
prey was a disgusting morsel." Under
these circumstances it would
be highly advantageous to a caterpillar
to be instantaneously and certainly
recognised as unpalatable by
all birds and other animals.
Thus the most gaudy colours would
be serviceable, and might have
been gained by variation and
the survival of the most easily-recognised
individuals.
This hypothesis
appears at first sight very
bold, but when it
was brought before the Entomological
Society* it was supported by
various statements; and Mr. J.
Jenner Weir, who keeps a large
number of birds in an aviary,
informs me that he has made many
trials, and finds no exception
to the rule, that all caterpillars
of nocturnal and retiring habits
with smooth skins, all of a green
colour, and all which imitate
twigs, are greedily devoured
by his birds. The hairy and spinose
kinds are invariably rejected,
as were four conspicuously-coloured
species. When the birds rejected
a caterpillar, they plainly shewed,
by shaking their heads, and cleansing
their beaks, that they were disgusted
by the taste.*(2) Three conspicuous
kinds of caterpillars and moths
were also given to some lizards
and frogs, by Mr. A. Butler,
and were rejected, though other
kinds were eagerly eaten. Thus
the probability of Mr. Wallace's
view is confirmed, namely, that
certain caterpillars have been
made conspicuous for their own
good, so as to be easily recognised
by their enemies, on nearly the
same principle that poisons are
sold in coloured bottles by druggists
for the good of man. We cannot,
however, at present thus explain
the elegant diversity in the
colours of many caterpillars;
but any species which had at
some former period acquired a
dull, mottled, or striped appearance,
either in imitation of surrounding
objects, or from the direct action
of climate, &c., almost certainly
would not become uniform in colour
when its tints were rendered
intense and bright; for in order
to make a caterpillar merely
conspicuous, there would be no
selection in any definite direction.
* Proceedings, Entomological
Society, Dec. 3, 1866, p. xlv.,
and March 4, 1867, p. lxxx.
*(2) See Mr.
J. Jenner Weir's Paper on "Insects and Insectivorus
Birds," in Transact. Ent. Soc.,
1869, p. 21; also Mr. Butler's
paper, ibid., p. 27. Mr. Riley
has given analogous facts in
the Third Annual Report on the
Noxious Insects of Missouri,
1871, p. 148. Some opposed cases
are, however, given by Dr. Wallace
and M. H. d'Orville; see Zoological
Record, 1869, p. 349.
Summary and Concluding Remarks
on Insects.- Looking back to
the several Orders, we see that
the sexes often differ in various
characters, the meaning of which
is not in the least understood.
The sexes, also, often differ
in their organs of sense and
means of locomotion, so that
the males may quickly discover
and reach the females. They differ
still oftener in the males possessing
diversified contrivances for
retaining the females when found.
We are, however, here concerned
only in a secondary degree with
sexual differences of these kinds.
In almost all the Orders, the
males of some species, even of
weak and delicate kinds, are
known to be highly pugnacious;
and some few are furnished with
special weapons for fighting
with their rivals. But the law
of battle does not prevail nearly
so widely with insects as with
the higher animals. Hence it
probably arises, that it is in
only a few cases that the males
have been rendered larger and
stronger than the females. On
the contrary, they are usually
smaller, so that they may be
developed within a shorter time,
to be ready in large numbers
for the emergence of the females.
In two families of the Homoptera
and in three of the Orthoptera,
the males alone possess sound-producing
organs in an efficient state.
These are used incessantly during
the breeding-season, not only
for calling the females, but
apparently for charming or exciting
them in rivalry with other males.
No one who admits the agency
of selection of any kind, will,
after reading the above discussion,
dispute that these musical instruments
have been acquired through sexual
selection. In four other Orders
the members of one sex, or more
commonly of both sexes, are provided
with organs for producing various
sounds, which apparently serve
merely as call-notes. When both
sexes are thus provided, the
individuals which were able to
make the loudest or most continuous
noise would gain partners before
those which were less noisy,
so that their organs have probably
been gained through sexual selection.
It is instructive to reflect
on the wonderful diversity of
the means for producing sound,
possessed by the males alone,
or by both sexes, in no less
than six Orders. We thus learn
how effectual sexual selection
has been in leading to modifications
which sometimes, as with the
Homoptera, relate to important
parts of the organisation.
From the reasons assigned in
the last chapter, it is probable
that the great horns possessed
by the males of many lamellicorn,
and some other beetles, have
been acquired as ornaments. From
the small size of insects, we
are apt to undervalue their appearance.
If we could imagine a male Chalcosoma
(see fig. 16), with its polished
bronzed coat of mail, and its
vast complex horns, magnified
to the size of a horse, or even
of a dog, it would be one of
the most imposing animals in
the world.
The colouring of insects is
a complex and obscure subject.
When the male differs slightly
from the female, and neither
are brilliantly-coloured, it
is probable that the sexes have
varied in a slightly different
manner, and that the variations
have been transmitted by each
sex to the same without any benefit
or evil thus accruing. When the
male is brilliantly-coloured
and differs conspicuously from
the female, as with some dragonflies
and many butterflies, it is probable
that he owes his colours to sexual
selection; whilst the female
has retained a primordial or
very ancient type of colouring,
slightly modified by the agencies
before explained. But in some
cases the female has apparently
been made obscure by variations
transmitted to her alone, as
a means of direct protection;
and it is almost certain that
she has sometimes been made brilliant,
so as to imitate other protected
species inhabiting the same district.
When the sexes resemble each
other and both are obscurely
coloured, there is no doubt that
they have been in a multitude
of cases so coloured for the
sake of protection. So it is
in some instances when both are
brightly-coloured, for they thus
imitate protected species, or
resemble surrounding objects
such as flowers; or they give
notice to their enemies that
they are unpalatable. In other
cases in which the sexes resemble
each other and are both brilliant,
especially when the colours are
arranged for display, we may
conclude that they have been
gained by the male sex as an
attraction, and have been transferred
to the female. We are more especially
led to this conclusion whenever
the same type of coloration prevails
throughout a whole group, and
we find that the males of some
species differ widely in colour
from the females, whilst others
differ slightly or not at all
with intermediate gradations
connecting these extreme states.
In the same manner as bright
colours have often been partially
transferred from the males to
the females, so it has been with
the extraordinary horns of many
lamellicorn and some other beetles.
So again, the sound-producing
organs proper to the males of
the Homoptera and Orthoptera
have generally been transferred
in a rudimentary, or even in
a nearly perfect condition, to
the females; yet not sufficiently
perfect to be of any use. It
is also an interesting fact,
as bearing on sexual selection,
that the stridulating organs
of certain male Orthoptera are
not fully developed until the
last moult; and that the colours
of certain male dragon-flies
are not fully developed until
some little time after their
emergence from the pupal state,
and when they are ready to breed.
Sexual selection
implies that the more attractive
individuals
are preferred by the opposite
sex; and as with insects, when
the sexes differ, it is the male
which, with some rare exceptions,
is the more ornamented, and departs
more from the type to which the
species belongs;- and as it is
the male which searches eagerly
for the female, we must suppose
that the females habitually or
occasionally prefer the more
beautiful males, and that these
have thus acquired their beauty.
That the females in most or all
the Orders would have the power
of rejecting any particular male,
is probable from the many singular
contrivances possessed by the
males, such as great jaws, adhesive
cushions, spines, elongated legs, &c.,
for seizing the female; for these
contrivances shew that there
is some difficulty in the act,
so that her concurrence would
seem necessary. Judging from
what we know of the perceptive
powers and affections of various
insects, there is no antecedent
improbability in sexual selection
having come largely into play;
but we have as yet no direct
evidence on this head, and some
facts are opposed to the belief.
Nevertheless, when we see many
males pursuing the same female,
we can hardly believe that the
pairing is left to blind chance-
that the female exerts no choice,
and is not influenced by the
gorgeous colours or other ornaments
with which the male is decorated.
If we admit that the females
of the Homoptera and Orthoptera
appreciate the musical tones
of their male partners, and that
the various instruments have
been perfected through sexual
selection, there is little improbability
in the females of other insects
appreciating beauty in form or
colour, and consequently in such
characters having been thus gained
by the males. But from the circumstance
of colour being so variable,
and from its having been so often
modified for the sake of protection,
it is difficult to decide in
how large a proportion of cases
sexual selection has played a
part. This is more especially
difficult in those Orders, such
as Orthoptera, Hymenoptera, and
Coleoptera, in which the two
sexes rarely differ much in colour;
for we are then left to mere
analogy. With the Coleoptera,
however, as before remarked,
it is in the great lamellicorn
group, placed by some authors
at the head of the Order, and
in which we sometimes see a mutual
attachment between the sexes,
that we find the males of some
species possessing weapons for
sexual strife, others furnished
with wonderful horns, many with
stridulating organs, and others
ornamented with splendid metallic
tints. Hence it seems probable
that all these characters have
been gained through the same
means, namely sexual selection.
With butterflies we have the
best evidence, as the males sometimes
take pains to display their beautiful
colours; and we cannot believe
that they would act thus, unless
the display was of use to them
in their courtship.
When we treat of birds, we shall
see that they present in their
secondary sexual characters the
closest analogy with insects.
Thus, many male birds are highly
pugnacious, and some are furnished
with special weapons for fighting
with their rivals. They possess
organs which are used during
the breeding-season for producing
vocal and instrumental music.
They are frequently ornamented
with combs, horns, wattles and
plumes of the most diversified
kinds, and are decorated with
beautiful colours, all evidently
for the sake of display. We shall
find that, as with insects, both
sexes in certain groups are equally
beautiful, and are equally provided
with ornaments which are usually
confined to the male sex. In
other groups both sexes are equally
plain-coloured and unornamented.
Lastly, in some few anomalous
cases, the females are more beautiful
than the males. We shall often
find, in the same group of birds,
every gradation from no difference
between the sexes, to an extreme
difference. We shall see that
female birds, like female insects,
often possess more or less plain
traces or rudiments of characters
which properly belong to the
males and are of use only to
them. The analogy, indeed, in
all these respects between birds
and insects is curiously close.
Whatever explanation applies
to the one class probably applies
to the other; and this explanation,
as we shall hereafter attempt
to shew in further detail, is
sexual selection. |