proportions; the sides and back of it are often armed with points.
The scutellum, or escutcheon, is the lower part of the body, and is
generally of a triangular form; though it adheres to the thorax, it is
easily distinguished therefrom by its figure, and often by an
intervening suture. It seems intended to assist in expanding the wings.
The sternum is situated on the under part of the thorax; in some species
it is pointed behind, as in the elateres; in others, bifid, as in some
of the dytisci.
OF THE ABDOMEN OF INSECTS.
The abdomen, or under part of the body, contains the stomach, the
intestines, the air vessels, &c. It is composed of several rings or
segments, so that it may be moved in various directions, or lengthened
and shortened at pleasure; in some it is formed of one piece only. It is
perforated with spiracula, or breathing holes, and is terminated by the
tail.
The spiracula are small oblong holes or pores placed singly one on each
side of every ring of the abdomen; these are the means or instruments of
respiration, supply the want of lungs, and form a peculiar
characteristic of insects.
OF THE LIMBS OF INSECTS.
By the limbs are here meant the instruments used by the insect both for
motion and defence. They are, alæ, the wings; halteres, the poisers;
pedes, the legs; cauda, the tail; and aculeus, the sting.
OF THE WINGS OF INSECTS.
The wings are those organs by which the insect is enabled to fly; some
have only two, others are furnished with four, two on each side; these
are, in some, of the same size; in others, the superior ones are much
larger than the inferior: Linnæus has made them the foundation of the
order into which he has divided this numerous class of beings. The
variety in the form and structure of the wings is almost infinite; the
beauty of their colouring, the art with which they are connected to the
body, the curious manner in which some are folded up, the fine
articulations provided for this purpose, by which they are laid up in
their cases when out of use, and yet are ready to be extended in a
moment for flight; together with the various ramifications, by which the
nourishing juices are circulated, and the wing strengthened, afford a
fund of rational investigation highly entertaining; exhibiting,
particularly when examined by the microscope, a most wonderful display
of divine wisdom and power. The more delicate and transparent wings are
covered and protected by elytra, or cases, which are generally hard and
opake. The wings of moths and butterflies are mostly farinaceous,
covered with a fine dust; by the assistance of the microscope, we
discover that this dust is a regular assemblage of organized scales,
which will be more particularly noticed hereafter.
The following names are made use of to describe the different kinds of
wings. They are first distinguished, with respect to their surfaces,
into superior and inferior. The part next the head is called the
anterior part; that nearer the tail, the posterior part. The interior
part is that next the abdomen; the exterior part is the outermost edge.
Those wings are termed plicatiles, which are folded when the insect is
at rest, as in the wasp. Planæ; those which are incapable of being
folded. Erectæ; whose superior surfaces are brought in contact when the
insect is at rest, as in the ephemera, papiliones, &c. Patentes; if they
are extended horizontally when the insect is at rest, as in the phalænæ
geometræ. Incumbentes; those insects which, when they are not in motion,
cover horizontally with their wings the superior part of the abdomen.
Deflexæ; those are also incumbentes, but not horizontally, the outer
edges declining towards the sides, Reversæ, are also deflexæ, with this
addition, that the edges of the inferior wings project from under the
anterior part of the superior ones. Dentatæ; with serrated or scolloped
edges. Caudatæ; in these some of the fibres of the wings are extended
beyond the margin into a kind of tail. Reticulatæ; when the veins or
membranes of the wings put on the appearance of net-work.
The wings are further distinguished by their ornaments, being painted
with spots, maculæ; bands, fasciæ; streaks, strigæ: when these are
extended lengthways, they are called lines, linæ; and if with dots,
punctæ; one or more rings are termed eyes, ocelli; if the spots are
shaped like a kidney, they are termed stigmata.
The elytra, or crustaceous cases of the wings are extended when the
insect flies, and shut when it rests, forming a longitudinal suture down
the middle of the back; they are of various shapes, and distinguished by
the following names:
Abbreviata; when they are shorter than the abdomen. Truncata; when their
extremities terminate in a transverse direct line. Fastigiata; when of
equal or greater length than the abdomen, and terminating in a
transverse line. Serrata; having their external margins edged with teeth
or notches. Spinosa; when their exterior surfaces are covered with small
sharp points. Scabra; when they are very rough. Striata; marked with
slender longitudinal furrows. Porcata; having sharp longitudinal ridges.
Sulcata; with deep furrows. They are likewise distinguished by the
denomination of Hemelytra, when their cases are neither so hard as the
elytra, nor so delicate as the transparent wings.
OF THE HALTERES OR POISERS OF INSECTS.
Under the wings of most insects which have only two, there is a small
head placed on a stalk, frequently under a little arched scale; these
are called halteres, poisers; they appear to be rudiments of the hinder
wings: it has been supposed that they serve to keep the body in
equilibrio when the insect is flying.
OF THE ELYTRA, AND WINGS UNDER THE ELYTRA.
I have already observed, that the delicate and transparent wings of many
insects are covered and protected by elytra, or cases, which also in
some measure act as wings.
These exterior cases are harder and more opake than the wings under
them; they are generally highly polished, and often enriched with
various colours, adorned with ornamental flutings, and studded with
brilliants, whose beauties are beyond description. All these ornaments
are united in the curculio imperialis,[56] or diamond beetle, one of the
richest and most magnificent creatures in nature; the head, the wings,
the legs, &c. are curiously beset with scales of a most splendid
appearance, outvying the ruby, saphire, and emerald, forming in
miniature one of the most noble phenomena that the colours of light can
exhibit. It is said, that in the Brazils, from whence they come, it is
almost impossible to look at them on a sunny day, when they are flying
in little swarms, so great is the glowing splendor of their heightened
colours.
[56] Fabriciús Spec. Ins. 184. 129.--Drury. Ins. 2 Tab. 33, Fig. 1.
The strength and hardness of the elytra are admirably adapted to the
various purposes of the insects to which they are appropriated; at the
same time that they protect the tender wings beneath them, they serve
as a shield to the body; while the ribs, and other prominences,
contribute to lessen the friction and diminish the pressure to which
they are often exposed. In most of these insects, the under wing is
longer and larger than the exterior one, so that it is obliged to be
bent and folded up, in order to lye under the elytra; for this purpose
they are furnished with strong muscles, and proper articulations to
display or conceal them at pleasure.
OF THE WINGS OF THE FORFICULA AURICULARIA, OR EARWIG.
Fig. 1. Plate XIV. is a magnified view of the wing of an earwig. Fig. 2.
the natural size. Though the insect is so very common, yet few people
know that it has wings, and fewer yet have seen them; they are of a
curious and elegant texture, and wonderful structure. The upper part is
crustaceous and opake, while the other part is beautifully transparent.
They fold up into a very small compass, and lie neatly concealed under
the elytra, which are not more than a sixth part of the wing in size.
They first fold back the parts A B, and then shut up the ribs like a
fan; the strong muscles used for this purpose are seen at the upper part
of the figure. The ribs are extended from the center to the outer edge,
others are extended only from the edge about half-way; but they are all
united by a kind of band, at a small, but equal distance from the edge;
the whole evidently contrived to strengthen the wing, and facilitate the
various motions thereof; so that, in these wings you find all the
motions that are in the most elaborate and portable umbrellas, executed
with a neatness and elegance surpassing description. The earwig is a
very destructive animal, doing considerable injury to most kinds of wall
fruit, to carnations, and other fine flowers, &c. and as they only feed
in the night, they escape the search of the gardener. Reeds open at both
ends, and placed among fruit trees, are a good trap for them, as they
croud into these open channels, and may be blown out into a tub of
water. As they conceal themselves in the day-time, those that are
curious in flowers place tobacco pipes, lobster claws, &c. on the top of
their garden sticks, in order to catch them. This insect differs very
little in appearance in its three different states. De Geer asserts,
that the female sits on her eggs, and broods over the young ones, as a
hen does over her chickens.
OF THE WINGS OF THE HEMEROBIUS PERLA.
So infinite is the variety displayed in the disposition, structure, and
ornaments of the wings of insects, that only to enumerate them would
fill many pages; I must leave this subject to be further pursued by the
reader, contenting myself with presenting him with the view of a wing of
the hemerobius perla, as it appears under the microscope. The insect to
which it belongs, has acquired the name of hemerobius, from the
shortness of its life, as it seldom lives more than two or three days in
the fly state. Linnæus has placed it in his fourth class, among those
insects which have four transparent wings and no sting. The body of the
insect is of a fine green colour; the eyes appear like two delicate
beads of burnished gold, whence it is by many called the golden eye. The
wings are delicate and elegant, nearly of a length, and exactly similar;
they are composed of a beautiful thin transparent membrane, furnished
with slender fine ribs, regularly and elegantly disposed, adorned with
hairs, and slightly tinged with green. Fig. 1. Plate XV. exhibits its
magnified appearance; Fig. 2. the natural size.
OF THE WINGS OF MOTHS AND BUTTERFLIES.
The wings of these insects are mostly farinaceous, being covered with a
fine dust, which renders them opake, and produces those beautiful and
variegated colours by which they are so richly adorned, and so profusely
decked. If this be wiped off, you find the remaining part, or naked
wing, to consist of a number of ribs, like those in the leaves of
plants; but of a crustaceous or talcy nature; the largest rib runs along
and fortifies the exterior edge of the wing; the interior edge is
strengthened by a smaller vessel or rib. The ribs are all hollow, by
which means the wing, though comparatively large, is very light. The
substance between the ribs, and which constitutes the body of the wing,
resembles talc,[57] surprizingly thin and transparent; as this is
extremely tender, one use of the scales may be to protect it from
injuries. When the moth emerges from the chrysalis, the wings are soft
and thick, and if they be examined in that state, will be found to
consist of two membranes, that may be raised up and separated, by
blowing between them with a small tube: the ribs lie between these
membranes. You may with the assistance of glasses discover certain
strait and circular rows of extremely minute holes, running from rib to
rib, or forming figures in the intermediate spaces, which seem to answer
to the figures and variegations on the complete wing, and are probably
the sockets for the stalks or stems of the small scales.
[57] As the author’s idea of this substance being of the nature of
talc, does not appear correct, and I cannot find that entomologists
are agreed in the definition of it, I shall just give the following
extract on the subject from the Cyclopœdia by Rees, and submit the
decision to the reader.
“The substance which connects and fills up the spaces between these
ribs, is of so peculiar a nature, that it is not easy to find any name
to design it by, at least there is no substance that enters the
composition of the bodies of the larger animals, that is at all
analogous to it. It is a white substance, transparent and friable, and
seems indeed to differ in nothing from that of the large and thick
ribs, but in that it is extended into thin plates; but this is saying
little toward the determining what it really is, since we are as much
at a loss to know by what name to call the substance they are composed
of. Malpighi indeed calls them bones; but though they do serve in the
place of bones, rendering the wing firm and strong, &c. yet, when
strictly examined, they do not appear to have any thing of the
structure of bones, but appear rather of the substance of scales, or
of that sort of imperfect scales, of which, the covering of
crustaceous insects is composed.” EDIT.
Ever since the microscope was invented, the dust that covers these wings
has engaged the attention of microscopic observers; as by this
instrument it is found to be a regular collection of organized scales of
various shapes, and in whose construction there is as much symmetry, as
there is beauty in their colours. A view of some of these scales, as
they appear in the microscope, is exhibited at F E H I, in Fig. 7. Plate
XVI. and in Fig. 8. of the natural size. Their shapes are not only very
different in moths of various species, but those on the same moth are
also found to differ. Of the scales, some are so long and slender that
they resemble hairs, except that they are a little flattened and divided
at the ends; some are short and broad; some are notched at the edges,
others smooth; some are nearly oval, while others are triangular: they
are mostly furnished with a short stalk or stem to fix them to the wing.
With the microscope, a variety of large stripes or ribs are to be
discovered; between these larger lines, minuter ones may be seen with a
deep magnifier. The larger stripes rise in general from the exterior
notches; some have a rib running down the middle, through their whole
length. The upper and under parts of the wing are equally supplied with
them.
The regular arrangement of these plates, one beside and partly covering
the other, as in the tiling of an house, is best seen by examining a
wing in the opake microscope. The prodigious number of small scales
which cover the wings of these beautiful insects, is a sure proof of
their utility to them, because they are given by HIM who makes nothing
in vain.
That the lively and variegated colours, which adorn the wings of the
moth and butterfly, arise from the small scales or plates that are
planted therein, is very evident from this, that if they be brushed off
from it, the wing is perfectly transparent: but whence this profusion
and difference of colour on the same wing? is a question as difficult to
resolve, as that of Prior, when he asks.
“Why does one climate and one soil endue }
The blushing poppy with a crimson hue, }
Yet leave the lilly pale, and tinge the violet blue?” }
As the wings of the moths and butterflies are very light, they can
support themselves for a long time in the air; their manner of flying is
ungraceful, generally moving in a zigzag line, to the right and to the
left, alternately ascending and descending; this undulating motion
however has its uses, as it disappoints the birds who chase them in
taking aim; by which means they frequently elude their pursuit, though
continued for a considerable time.
Dr. Hooke[58] endeavoured to investigate the nature of the motions of
the wings of insects; and, although he was not able, from the
experiments he made, to give a satisfactory account of them, yet as they
may be useful to some future inquirer, and lead him more readily into
the path of truth, I hope an extract therefrom will not prove
unacceptable to the reader. To investigate the mode or manner of moving
their wings, he considered with attention those spinning insects that
suspend, or as it were poise themselves in one place in the air,
without rising or falling, or even moving backwards or forwards; by
looking down on these, he could, by a kind of faint shadow, perceive the
utmost extremes of the vibratory motion of their wings; the shadow,
while they were thus suspended, was not very long, but was lengthened
when they endeavoured to fly forwards. He next tried by fixing the legs
of a fly upon the top of the stalk of a feather with glue, wax, &c. and
then making it endeavour to fly away; he was thereby able to view it in
any posture. From hence he collected, that the extreme limits of the
vibrations were usually somewhat about the length of the body distant
from each other, often shorter, and sometimes longer. The foremost limit
was generally a little above the back, and the hinder one somewhat
beneath the belly; between these, to judge by the sound, they seemed to
move with an equal velocity. The manner of their moving them, if a just
idea can be formed by the shadow of the wing, and a consideration of its
nature and structure, seemed to be this: the wing being supposed to be
in the extreme limit, it is then nearly horizontal, the forepart only
being a little depressed; in this situation the wing moves to the lower
limit; before it arrives at this, the hinder part begins to move
fastest; the area of the wing begins to dip behind, and in that posture
it seems to be moved to the upper limit back again. These vibrations,
judging by the sound, and comparing them with a string tuned in unison
thereto, consist of many hundreds, if not thousands, in a second of
time. The powers of the governing faculty of the insect, and the
vivacity of its sensations, whereby every organ is stimulated to act
with so much velocity and regularity, surpass our present comprehension.
[58] Hooke’s Micrographia, p. 172.
PEDES THE FEET, AND LEGS OF INSECTS.
These are admirably adapted for their intended service, to give the most
convenient and proper motion, and, from the variety in their
construction, their various articulations, &c. furnish the microscopic
observer with an abundance of curious and interesting objects: the most
general number is six; many of the class aptera have eight, as the
spider; the crab has ten; the oniscus fourteen; the julus has from
seventy to one-hundred and twenty on each side. The legs of those
insects that have not more than ten, are affixed to the trunk; while
those that exceed that number, have part fixed to the trunk, the rest to
the abdomen.
The legs of insects are generally divided into four parts. The first,
which is usually the largest, is called the femur; the second, or tibia,
is joined to the former, and is commonly of the same size throughout,
and longer than the femur; this is followed by the third part, which is
distinguished by the name of tarsus, or foot; it is composed of several
joints, the one articulated to the other, the number of rings varying in
different insects; the tarsus is terminated by the unguis, or claw.
The writers on natural history, in order to render their descriptions
clear and accurate, have given several names to the legs of insects,
from the nature of the motions produced by them. Thus cursorii, from
that of running; these are the most numerous. The saltatorii, those that
are used for leaping; the thighs of these are remarkably large, by which
means they possess considerable strength and power to leap to great
distances. The natatorii, those that serve as oars for swimming; the
feet of these are flat and edged with hairs, possessing a proper surface
to strike against the water, as in the dytiscus, notonecta, &c. Such
feet as have no claws are termed mutici. The chelæ, or claws, are an
enlargement of the extremity of the fore feet, each of which is
furnished with two lesser claws, which act like a thumb and finger, as
in the crab. The under part of the feet in some insects is covered with
a kind of brush or sponge, by which they are enabled to walk with ease,
on the most polished substances, and in situations from which it would
seem they must necessarily fall.
Motion is one of the principal phenomena of nature; it is as it were the
soul of our system, and is as admirable in the smallest animal, as in
the universe at large. It is the principal agent in producing all that
diversity and change which perpetually affect every object in the
creation. The motions of animals are proportioned to their weight and
structure, a flea can leap to the distance of at least two hundred times
its own length; were an elephant, a camel, or an horse to leap in the
same proportion, their weight would crush them to atoms. The same remark
is applicable to spiders, worms, and other insects; the softness of
their texture, and the comparative smallness of their specific gravity,
enable them to fall without injury from heights that would prove fatal
to larger and heavier animals.[59]
[59] The parts of some of the larger animals are, however, so
admirably constructed for swiftness, as to enable them to perform
surprizing acts of agility; for instance, the Siberian jerboa, mus
saliens, Pennant; this animal springs forward by successive leaping so
very nimbly, that it is said to be very difficult for a man well
mounted to overtake it; it is about the size of a large rat. The
kanguroo, opossum of Pennant, macropus giganteus, Shaw, leaps to so
uncommon a height, and to so great a distance, as to outstrip the
swiftest greyhound; its size is that of a full-grown sheep. Accurate
coloured figures of both these extraordinary animals are given in that
elegant work, the Naturalist’s Miscellany. EDIT.
Many insects can only move the thigh in a vertical direction, while
others can move it in a variety of ways. The progressive motion of
insects, and the various methods employed to effect it, will be found a
very curious and important subject, and well worthy the attention of the
naturalist. The intelligent mechanic will not find it lost labour if he
bestow some time on the same subject. Very little has been done on this
head, and that principally by Reaumur, in his excellent Memoires; and
by M. Weiss, in a Memoir published in the Journal de Physique for 1771.
The reader may also consult Borelli de Motu Animalium.
OF THE TAIL AND STING OF INSECTS.
Cauda, the tail, terminates the abdomen, and is constructed in a
wonderful manner for answering the purposes for which it is formed,
namely, to direct the motion of the insect, to serve as an instrument of
defence, or for depositing the eggs; the figure and size thereof varying
in each genus and its families. In most insects it is simple, simplex,
and yet capable of being extended or drawn back at pleasure; in others,
elongata, elongated, as in the crab and scorpion; setacea, shaped like a
bristle, as in the raphidia; triseta, with three appendages like
bristles, as in the ephemera; in some it is forked, furcata, as in the
podura; and in others it is furnished with a pair of forceps, forcipata,
as in the forficula; in the blatta, grylli, and others, it is foliosa,
or like a leaf; in the scorpion and panorpa it is telifera, furnished
with a dart or sting. Further particulars may be obtained from the
Philosophia Entomologica of Fabricius.
Aculeus, or the sting, is an instrument with which insects wound and
instil a poison; the sting generally proceeds from the under part of the
last ring of the belly: in some it is sharp and pointed, in others
serrated or formed like a saw. It is used by many insects both as an
offensive and defensive weapon; by others it is only used to pierce the
substances where they mean to deposit their eggs. This instrument cannot
be properly seen or known, but with the assistance of a microscope.
OF THE STING OF A BEE.