of the male is densely bearded, but not of the female[714].--Some
_Hymenoptera_, as _Ammophila_ Kirb. and _Stigmus_ Jurine, have
the upper lip of the male clothed with silver pile, while that
of the female is not so ornamented. The legs of some bees are
distinguished in the sexes by a difference in their _clothing_. That
observable in those of the hive-bee has been before noticed[715].
In _Andrena_ of Latreille[716] the posterior tibia of the female is
covered externally with a dense brush of hairs, for collecting the
pollen; and the posterior legs at their base have a curled lock of
hair--which are not to be found in the male[717]. In _Dasypoda_,
_Melecta_, _Anthophora_, _Centris_, _Epicharis_, &c. of the same
author, the first joint of the tarsus of the female, and in
_Xylocopa_ almost the whole tarsus, is also similarly signalized from
that of the other sex. In _Bombus_, as in the hive-bee, the posterior
tibiæ of the females and neuters are furnished with a basket of hairs
for carrying their pollen paste, which you will in vain look for in
the male[718]. The latter, however, in some species of this tribe are
distinguished from the former by the longer hairs of their legs, but
not in the posterior ones. Thus, in _Anthophora retusa_ the first
joints of the intermediate tarsus are bearded internally with a thin
fringe of long hairs, and the first externally with a triangular one
of short ones at the apex: but what is most remarkable, the last or
unguicular joint, which in almost every other bee is naked, is on
both sides fringed with long hairs[719]. In that remarkable genus
_Acanthopus_ Illig., of which the male only is known, the first and
last joint of the intermediate tarsus have a dense external brush
of stiff hairs, which probably is also a sexual character[720].
Another sexual kind of clothing is exhibited by the females of those
bees that have their labrum or upper-lip inflexed (_Megachile_
Latr.)[721]. Their abdomen is covered underneath with a brush of
stiff hairs, involved in which they carry the pollen they collect.
In the males of some of this tribe, as of _M. Willughbiella_, the
first four joints of the anterior tarsus on their inner side have a
long dense fringe of incurved hairs[722]: a circumstance also to be
found in the same sex of _Xylocopa latipes_, in which the claw-joint
also is bearded[723]. In _Andrena_ Latr. the last dorsal segment of
the abdomen of the same sex is fringed, while that of the male is
naked[724]. In the humble-bees (_Bombus_), the mandibles of the male
are bearded with curled hairs, while those of the females and neuters
are without them. Some bees, as _Andrena_ and _Halictus_ Latr., have
the anus of the female bearded, and that of the male naked: in some
_Bombyces_ the reverse takes place.
iii. With regard to the general _shape_ of their body, the male and
female usually resemble each other: but there are some exceptions to
this rule. The male of the hive-bee is much thicker and more clumsy
than either the female or the worker; but in _Halictus_ Latr. the
males are nearly cylindrical in shape, and very narrow; while the
other sex are oblong or ovate, especially their abdomen: and in
_Andrena_ Latr. the former are much slenderer than the females, and
of a more lanceolate shape. But a still more striking difference
in this respect between the sexes is exhibited by some species of
the genus _Ptinus_ F., in which the male is long and slender, and
the female short and thick. This, in more than one instance, has
occasioned them to be mistaken for distinct insects: thus, _P.
Lichenum_ and _P. similis_, _P. ovatus_ and _P. testaceus_, of Mr.
Marsham, are mere sexual varieties. But the most entire abalienation
of shape at present known, is that which distinguishes the male from
the female _Coccus_; these are so completely dissimilar as scarcely
to have any part in common. In _Bombyx vestita_ F., and others of
the same family, while the males are of the ordinary conformation of
the order, the females are without even the slightest rudiments of
wings; they have no antennæ, the legs are extremely short, not longer
than those of the caterpillar; and the body is entirely destitute
of scales, so that they altogether assume the exact appearance of
hexapod larvæ[725]. A conformation nearly similar takes place in the
female of _Tinea Lichenella_; but in this the feet are longer, and
the anus is furnished with a long retractile ovipositor[726].
iv. In many cases, the structure of particular _parts_ and _organs_
of the body differs in the sexes. As the facts connected with this
part of our present subject are extremely numerous and various,
it will be convenient to subdivide it, and consider the sexual
characters that distinguish--the _Head_, _Trunk_, and _Abdomen_ of
insects, and their several appendages.
1. The _Head_. This part in some females is considerably larger than
it is in the male. This is the case with the ants, and several other
_Hymenoptera_; while in some _Andrenæ_, as _A. hæmorrhoidalis_, and
_Staphylinidæ_, as _St. olens_, that of the male is the largest. But
in none is the difference more conspicuous than in the stag-beetle
(_Lucanus_); in which genus the male not only exceeds the female
in the length of his mandibles, but also greatly in the size and
dimensions of his head. In the _Apion_ genus, the rostrum of the
female is generally longer and slenderer than that of her mate; and
in _Brentus_, the rostrum of one sex (probably the male) is long
and filiform, while in the other it is thick and short. This is
particularly visible in _B. dispar_ and _maxillosus_[727], &c.
One of the most striking distinctions of the males in this part of
their body, are those threatening horns, usually hollow, with which
the heads of many of the male lamellicorn insects and some others
are armed, and which give them some resemblance to many of the
larger quadrupeds. Many are _unicorns_, and have their head armed
with only a _single_ horn; which in some, as in _Oryctes_ Illig.,
_Dynastes Endymion_[728], &c. is very short; in others, very long,
as in _Dynastes Enema_, _Pan_, _Elephas_[729]. In one, again, it
is thick and robust; as in the clumsy _Dynastes Actæon_[730]: in
another very slender, as in _Onthophagus spinifer_[731]. With respect
to its direction in _Elephastomus proboscideus_ MacLeay, it is
horizontal[732] and straight; in _Phaleria cornuta_ horizontal and
broken, or the apex turning outwards and forming an angle with the
base[733]; in _Dynastes Hercules_ horizontal, and recurved at the
apex[734]; in _D. Actæon_, _Elephas_, and _Typhon_, recurving from
the base. In _Geotrupes dispar_ it is recurved, so that its point
exactly coincides with that of the porrected thoracic horn, with
which it forms a kind of forceps[735]. In _Copris lunaris_ F. and
_Diaperis horrida_, the horn is nearly upright[736]. In _Onthophagus
Xiphias_ it is dilated at the base, and reclining upon the thorax;
and at the apex attenuated, and bending forwards, or nodding.
In _Passalus cornutus_ it rises a little, and then bends wholly
forwards. In _Dynastes Milon_, a most remarkable beetle, it slopes
backwards in a waving line[737]; and in _Onthophagus spinifer_ it is
recurved and reclining.--In speaking of the direction of the horn,
you must recollect that it will vary in proportion as the head varies
from a horizontal position: so that an upright horn will become
inclined or reclined, as the head bends forwards or backwards; but
I speak of it as it appears when the head is horizontal. Again,
it varies in its teeth or branches. In _Dynastes Hercules_ it is
armed with several teeth. In _D. Elephas_ and _Actæon_ it has only
one large one at its upper base[738]. In _D. Milon_ it is serrated
above. In _D. Alcides_, _Tityus_, _Ægeon_, _Copris lunaris_, &c. the
horn is unarmed and simple at the apex. In _D. Oromedon_, _Gedeon_,
_Enema_, _Actæon_ and congeners, it is bifid. In some the horn is at
first a broad lamina or ridge, which terminates in two branches, as
in _Onthophagus Vacca_. In this the branches are straight; but in
another undescribed species in my cabinet (_O. Aries_ Kirby, MS.)
they are first bent inwards, and then at the apex a little recurved:
and in _D. dichotomus_ it is divided into two short branches, each of
which is bifid[739]. Other males emulate the bull, the he-goat, or
the stag, in having a _pair_ of horns on their head. In _Onthophagus
Taurus_, these arms in their curvature exactly resemble those of
the first of these animals[740]. In _Goliathus pulverulentus_, the
straight, robust, diverging, sharp horns are not unlike those of some
of the goat or gazel tribe. I have a beautiful little specimen in my
cabinet, (I believe collected by Mr. Abbott of Georgia,) in which the
horns have a lateral tooth, or short branch, like those of a stag;
and which I have therefore named _O. cervicornis_. In _O. Vacca_,
_Camelus_, &c. the horns are very short, and nearly perpendicular. In
the male of _Copris Midas_, the two longer perpendicular horns have
a deep cavity between them, which, together with its black colour,
give it a most demoniac aspect; so that you would think it more aptly
representative of a Beelzebub or _Beelzebul_ than a Midas[741],
or than _Phanæus Beelzebul_ MacL. A similar cavity is between the
occipital horns of _Diaperis hæmorrhoidalis_ Payk. Some species of
_Rynchænus_, as _R. Taurus_, have a pair of long horns upon the
rostrum of the male, the rudiments only of which are to be traced
in the female[742]. Other species go beyond any known quadrupeds in
the number of horns that arm their heads. Thus _Ditomus calydonius_
Bonelli, belonging to _Carabus_ L., has _three_ equal horns[743]. The
same number distinguishes _Onthophagus Bonasus_; but the intermediate
one is very short. In _Goliathus Polyphemus_ the middle horn, on
the contrary, is much longer and thicker than the lateral ones, and
forked at the apex; so that it looks as if it had four of these
weapons[744]. A little _Diaperis_ (_D. viridipennis_ F.), a native
of _Carolina_, has four horns upon the head of the male; namely,
two long ones on the occiput, and two short dentiform ones on the
nose. In a species nearly related to this, sent me by Professor Peck
from New England, there is a cavity between the two occipital horns.
The same number distinguishes _Onthophagus quadricornis_ (_Copris_
F.). The _situation_ also of the horns varies: In some it is in the
_middle_ of the head, as _Oryctes nasicornis_, _Copris lunaris_,
&c.: in others, as in _Onthophagus nuchicornis_, _Xiphias_, &c. it
is a process of the _occiput_ or hind-head; and in _O. Oryx_ F. the
two horns proceed from the _anterior_ part of the head. In the other
sex, in insects the head of whose males is armed with horns, they are
usually replaced by mere tubercles, or very short elevations, as you
may see in the female of _Copris lunaris_; or by transverse ridges,
as in the _Onthophagi_: or else the head is without arms, and quite
smooth, as in _Diaperis_, _Phaleria_, &c. What may be the use of
these extraordinary appendages, as well as those on the thorax, and
in some cases on the abdomen, (which I shall mention afterwards), to
the males, has not yet been ascertained. Whether the individuals of
this sex are more exposed to the attack of birds and other enemies,
in consequence of being more on the wing than the females, and are
therefore thus provided with numerous projecting points for defence,
is a question worth considering[745]. It is the only probable
conjecture on the _cui bono_ of these arms that I can at present
make. Under this head I ought to notice the remarkable membranous
process of an obovate shape, which like an umbrella covers the head
of _Acheta umbraculata_ F.[746] Whether the sharp curved horns which
arm this part in another _Acheta_ figured by Stoll[747], in an
incumbent posture, with their point towards the mouth, are a sexual
distinction, we are not informed,--probably they are.
The _organs_ of the head also present many sexual distinctions.
The upper lip (_labrum_) in _Halictus_ Latr., a tribe of wild bees,
in the female is furnished with an inflexed appendage, which is not
discoverable in that of the male[748]; and the shape of this lip in
_Sphecodes_ Latr. differs in the sexes[749]. Perhaps the horn or
tubercle observable on this part of some female _Nomadæ_ F.[750] may
be wanting in the male.
The under-lip (_labium_)--taken in a restricted sense for that
central part from which emerge the labial palpi, and which is often
considered as the mentum,--does not offer any striking variations in
the sexes. One, however, is of importance, as it helps to prove which
are the true female _Lucani_. In the male the labium is emarginate,
in the female it is intire. This may be seen both in _L. Cervus_
and _femoratus_, and probably in other species. The sculpture also
is different, the lip being smooth in the former and covered with
excavated _puncta_ in the latter. The tongue (_lingua_ or _ligula_)
of the sexes is usually the same; except in the hive-bee, in which
that of the neuters is longer than that of the male and female.
The upper-jaws (_mandibulæ_), however, often afford striking sexual
characters. The enormous protended ones of the common stag-beetle
(_Lucanus Cervus_) attract the attention of the most incurious
observer; and these are now generally allowed to be of this
description. Geoffroy and Mr. Marsham, indeed, have asserted that
they have taken _in coitu_ those with long mandibles: but as these
males are pugnacious, and attack each other with great fury, as Mr.
Sheppard informs me, it is not improbable that these gentlemen may
have mistaken a _battle_ for an _amour_: since not only have those
with long mandibles been often taken united with those that have short
ones[751], but the same difference obtains in the sexes of other
species. This is particularly observable in _Lucanus femoratus_, of
which I received from Brazil many specimens agreeing in every respect
except in this, that one had short and the other very long mandibles.
These organs vary in different specimens, as to the number of their
teeth and branches. They are singularly robust in _L. Alces_[752]; but
in none more threatening than in _L. Elephas_[753], in which they curve
outwards and downwards. In Mr. W. MacLeay's genus _Pholidotus_, they
are almost parallel to each other, and curve downwards; in _Lucanus
nebulosus_ Kirby, they assume a contrary direction[754]; as they do
likewise in _Lamprima_ Latr.[755] In _Lucanus Capreolus_ the points
close over each other[756]. In _Lethrus_ F. in the female, but not
the male, the mandible is armed below with a long incurved horn. In
_Lucanus serricornis_ they form a complete forceps[757]. In _Siagonium
quadricorne_ Kirby[758] the mandible is furnished at its base with an
exterior horn, which is probably a sexual distinction. The male of
_Synagris cornuta_, a kind of wasp, is still more conspicuous in this
respect; for from the upper side of the base of its straight slender
mandibles proceed a pair of crooked, decurved, tortuous, sharp horns,
not only longer than the mandible, but than the head itself[759].
Many sexual differences are observable in the mandibles of the various
tribes of bees (_Anthophila_ Latr.). Thus, in _Colletes_ Latr. the
_male_ mandible is more distinctly bidentate at the apex than the
female[760]: in _Sphecodes_ Latr. and others, the reverse of this takes
place[761]. Where these organs in both sexes are toothed at the apex,
they often vary in the number of teeth. Thus, the female of _Megachile
centuncularis_ Latr. has four teeth at the apex of its mandible, while
the male has only two[762]. In _M. Willughbiella_, though the mandibles
of both sexes have four teeth, yet those of the male are sharp, and
the two external ones the longest; while those of his mate are obtuse,
and all nearly equal in length[763]. In _Anthidium manicatum_ Latr.,
the former has only three teeth, while the latter has five[764].
The differences in this respect in the hive-bee have been before
noticed[765]; those of the humble-bees (_Bombus_ Latr.) are strikingly
distinguished from each other; the female mandible being very stout and
wide, constricted in the middle, and furrowed on its outer surface; and
the male, on the contrary, very slender at the apex, dilated at the
base, and without furrows[766].
Of all the organs of the head, none seem so little subject to _sexual_
variation as the under-jaws (_maxillæ_)[767]. I can bring forward only
one striking instance of it, and some degree of doubt rests even upon
that. In the genus _Nemognatha_ of Illiger, the maxillæ of the male are
elongated, narrow, setiform, and often involute or spiral, like those
of a bee or a butterfly. But that this is peculiar to the males is at
present only surmised[768]. I possess several species of the genus, all
of which are distinguished by long maxillæ; though in some they are as
long as the body, and in others scarcely half that length. _Gnathium_
Kirby is similarly characterized[769].
The _maxillary palpi_ occasionally differ in the sexes. In _Cerocoma_
those of the female are filiform, while the two intermediate joints
of those of the other sex are much thicker than the first and
the last[770]. In _Hylæcetus_ and _Lymexylon_, those of the male
are still more remarkable: they are pendent, the last joint very
large, and laciniated so as to form a tuft[771]. The female ones
grow gradually larger towards the end, but are not at all divided
there[772]. The palpi of male spiders are of a very different
structure from those of the other sex, terminating in a very complex
incrassated piece, which has been supposed to contain the organ
of generation; but this, according to Treviranus, is a mistaken
idea--that organ being, as usual, to be found in the abdomen[773]. In
the common gnat the palpi of the male are as long as the proboscis,
consist of five joints, and at the end are tufted with hairs; while
those of the female are scarcely one-fourth of its length, have only
three joints, and are not tufted. Whether the _labial palpi_ in any
genus differ in the sexes, I cannot affirm with certainty: I have
not, however, observed any such variation in them.
I shall next mention some organs of the head, in which the difference
between the sexes is often very striking and peculiar. You will
readily conjecture that I am speaking of the _antennæ_. And here
the advantage seems wholly on the side of the males: since in them
these wonderful instruments of unknown sensations are not only more
complex, but usually more elegant, than those of the other sex. You
will pardon me, therefore, if I enlarge a little more than ordinary
upon a subject so full of interest, and say something upon the
differences observable between the sexes--in the shape, magnitude,
and length, number of articulations, ramification and plumage, and
individual joints of their antennæ.
With regard to their _shape_, variations are sometimes observable
between the antennæ of the sexes; but this principally occurs in the
_Hymenoptera_ order. For instance, those of _Chelostoma maxillosa_,
a small bee that deposits its eggs in little holes in posts and
rails, are clavate in the female and filiform in the male[774]--a
circumstance that distinguishes in some degree those of _Sphecodes_,
_Halictus_, and _Andrena_ of Latreille, three other genera of
wild-bees[775]. In _Dinetus_ Jur. the male antennæ are moniliform at
the base, and filiform at the apex; the female, on the contrary, are
entirely filiform[776].
The antennæ of the sexes also sometimes differ in _magnitude_ and
_length_. This is the case in the three genera of wild bees just
mentioned; those of the female being thicker than those of the male,
while these last are longer than the former. But in this tribe
the males of the Fabrician genus _Eucera_ are most remarkable for
their long antennæ[777]. With regard to the different length of
these organs in the sexes, no insects are more distinguished than
some species of the capricorn-beetles (_Cerambyx_ L.). In _Lamia
Sutor_ the male antennæ are twice the length of the female; and in
another Brazilian species in my cabinet, related to _L. annulata_
(_Stenocorus_ F.), they are thrice their length. Some of the
_Anthribi_ F. approach the _Cerambycidæ_, not only in some other
characters, but also in this circumstance:--thus the antennæ of _A.
albinus_, a native of Britain, are vastly longer in the male than in
the female; and in _A. cinereus_ (_Macrocephalus_ Oliv.)[778], which
I suspect to be of the former sex, they are as long nearly as is
usual in the tribe just named, called in France capricorn-beetles.
I may here observe, that sometimes in the sexes a difference is also
to be found in the _direction_ or flexure of their antennæ. Thus in
_Scolia_ F., _Pepsis_ F. &c., in the males the antennæ are nearly
straight, but in the females convolute or subspiral. The reverse
of this takes place in _Epipone spinipes_, a kind of wasp, and its
affinities; and _Systropha_ Illig., a kind of bee: for in these the
male antenna is convolute at the apex[779], and the female straight.
In the various tribes of bees (_Anthophila_ Latr.), these organs in
the latter are what is denominated _broken_, the main body of the
antenna forming an angle with the first joints: but in the former
this does not take place.
The antennas of the sexes do not always agree in the _number_ of
joints. In the bees, and many other _Hymenoptera_, the male has
one more joint than the female; as is the case also in _Œdemera
notata_ (_Cantharis acuta_ Marsh.). In _Pteronus Laricis_, a kind of
saw-fly, the latter has only sixteen joints in its antennæ, while the
former has twenty-four[780]. In _Rhipicera marginata_, a beetle, the
beautiful antennæ of the male consist of thirty-two joints, while the
female has no more than eleven! In _Chelonus_ Jur. the male, on the
contrary, has the smallest number of joints, namely sixteen; while
the female has twenty-five[781].