apparatus is of a very curious construction, fitted for inflicting a
wound, and at the same time conveying poison into that wound.
The apparatus consists of two piercers conducted in a sheath, groove, or
director.
This groove is rather large at the base, but terminates in a point; it
is affixed to the last scale of the upper side of the abdomen by
thirteen thin scales, six on each side, and one behind the rectum. These
scales inclose the rectum all round, and are attached to each other by
thin membranes which allow of a variety of motions; three of them are
however attached more closely to a round and curved process, which comes
from the basis of the groove in which the sting lies, as also to the
curved arms of the sting which spread out externally. The two stings may
be said to begin by those two curved processes at their union with the
scales, and converging towards the groove at its base, which they enter,
and then pass along to its point.
The two stings are serrated or notched towards the points; they can be
thrust out a little way, and drawn within it. These parts are all moved
by very strong muscles, which give motions in almost all directions, but
most particularly outwards. It is wonderful how deep they will pierce
solid bodies with this sting.
To perform this by mere force, two things are necessary, power of
muscles, and strength of sting; neither of which they seem to possess in
a sufficient degree. Mr. J. Hunter thinks that it cannot be by simple
force, because the least pressure bends the sting in any direction. It
is probable that the serrated edges may assist, by cutting their way
like a saw.
The apparatus for the poison consists of two small ducts, which are the
glands that secrete the poison; these lie in the abdomen among the air
cells, they soon however unite into one oblong bag; at the opposite end
of which a duct passes out, which runs towards the angle where the two
stings meet, and, entering between them, forms a canal by the union of
the two stings at this point. From the serrated construction of the
stings the bee can seldom disengage them, and hence, when they pass into
materials of too strong a nature, the bee generally leaves them behind,
and often a part of the bowels therewith.[60]
[60] Phil. Trans. for 1792, page 189.
DISTINGUISHING CRITERIA OF INSECTS.
It has already been observed, that the bodies of insects are covered
with a hard skin, answering the purpose of an internal skeleton, and
forming one of the characters by which they are distinguished from other
animals. This external covering is very strong in those insects which,
from their manner of life, are particularly liable to great friction, or
violent compression; but is more tender and delicate in such as are not
so exposed. The skin of insects, like that of larger animals, is porous;
the pores in some species are very large; many insects often change or
cast off their skin; this exuvia forms an excellent object for the
microscope.
Another distinguishing criterion of insects is the colour of their
circulating fluid or blood, which is never red; this, at first sight,
seems liable to some objections, on account of the drop of red liquor
which is often procured from small insects when squeezed or pressed to
pieces. It does not appear, however, that this is the blood of the
little animal; when it existed as a worm there was no such appearance,
and when transformed to the perfect, or fly state, it is only found in
the eye, and not in the body, which would be the case if it circulated
in the veins of the insect. It is probable there is a circulation of
some fluid analogous to the blood in most insects: with the assistance
of the microscope this circulation may be perceived in many; but the
circulating liquor is not red.
To these discriminating characteristics we may also add the following
particulars:
1. That the body of insects is divided by incisuræ, or transversal
divisions, from whence they take their name.
2. That they are furnished with antennæ, which are placed upon the fore
part of the head; these are jointed and moveable in various directions.
3. That no insect in its perfect state, or after it has gone through all
its transformations, has less than six legs, though many have more.
There are some moths, whose two fore feet are so small, as scarcely to
entitle them to that name.
4. That insects have neither the organs of smell nor hearing; at least
they have not as yet been discovered, though it is reported that
Fabricius has lately found and described the organs of hearing in a
lobster.[61]
[61] That many insects are susceptible of a shrill or loud noise, is a
fact so well ascertained, as to be indisputable; but in what manner,
or by what organs the sensation is conveyed, is not so evident;
Barbut, however, supposes them to possess the sense of hearing in a
very distinct manner. Many insects, he observes, are well known to be
endued with the power of uttering sounds, viz. large beetles, bees,
wasps, common flies, gnats, &c. The sphinx atropos squeaks, when hurt,
nearly as loud as a mouse: this faculty certainly must be intended for
some purpose, and as they vary their cry occasionally, it appears
designed to give notice of pleasure or pain, or some affection in the
creature which possesses it. “The knowledge of their sounds,” says he,
“is undoubtedly confined to their tribe, and is a language
intelligible to them only; saving when violence obliges the animal to
exert the voice of nature in distress, craving compassion; then all
animals understand the doleful cry; for instance, attack a bee or wasp
near the hive or nest, or a few of them; the consequence will be, the
animal or animals, by a different tone of voice will express his or
their disapprobation or pain; that sound is known to the hive to be
plaintive, and that their brother or brethren require their
assistance, and the offending party seldom escapes with impunity. Now,
if they had not the sense of hearing, they could not have known the
danger their brother or brethren were in, by the alteration of their
tone.” Another proof, which he reckons still more decisive, was taken
from his observation on a spider, which had made a very large web on a
wooden railing, and was at the time in a cavity behind one of the
rails, at a considerable distance from the part where a fly had
entangled himself; the spider became immediately sensible of it,
though, from the situation of the rail, he could not possibly have
seen the fly. This observation, however, cannot be considered as
conclusive, as it is very probable that the spider was alarmed by the
tremulous motion of the threads of the web occasioned by the
fluttering of the fly, which he might well know how to distinguish
from their vibration by the wind. It is this author’s opinion, that
the organ of hearing is situated in the antennæ; he likewise supposes
that the organs of smell reside in the palpi or feelers. For his
reasoning on these subjects, see the Genera Insectorum, Preface, p.
vii. & seq. EDIT.
5. That they do not respire air by the mouth, but that they inspire and
exhale it by means of organs which are placed on the body.
6. That they move the jaws from right to left, not up and down.
7. That they have neither eye-lid nor pupil.
To these we may also add, that the mechanism resulting from the LIFE of
insects is not of so compound a nature as in animals of a larger size.
They have less variety of organs, though some of them are more
multiplied; and it is by the number and situation of these that their
rank in the great scale of beings is to be determined.
These characters are often united in the same insect; there are,
however, some species in which one or two of them are wanting.
The student in entomology, who wishes to attain a proper knowledge of
the science, and indeed every microscopic observer, desirous of
availing himself of the discoveries of others, and of communicating
intelligibly his own, will find it necessary to make himself conversant
with the various classes, genera, &c. into which insects have been
divided by Linnæus. Every system has its defects, and probably some may
be found in that of this truly celebrated naturalist, but the purpose of
science is answered by using those discriminations which are generally
adopted.
The following general idea of the Linnæan classes may serve as a
foundation for this knowledge: a more particular account may be obtained
by consulting the under-mentioned works.
Institutions of Entomology, a translation of Linnæus’s Ordines et Genera
Insectorum, or systematic arrangement of insects, &c. by Thomas
Pattinson Yeats.
Fundamenta Entomologiæ, or an Introduction to the Knowledge of Insects,
translated from Linnæus by W. Curtis, the ingenious author of Flora
Londinensis, the Botanical Magazine, &c.
The Genera Insectorum of Linnæus, exemplified by various Specimens of
English Insects, drawn from Nature, by James Barbut.[62]
[62] This work contains two excellent plates, illustrative of the
Distinctions of the Ordines and Genera Insectorum, by their antennæ,
tarsi of the feet, &c. EDIT.
Class the first. COLEOPTERA. The insects of this class have four wings;
the upper ones, called the elytra, are crustaceous, being of a hard
horny substance; these, when shut, form a longitudinal suture down the
back, as in the scarabæus, melolontha, or cockchaffer, &c.
2. HEMIPTERA. These have also four wings; but the elytra are different,
being half crustaceous, half membranaceous: the wings do not form a
longitudinal suture, but extend the one over the other, as in the
gryllus, grasshopper, &c.
3. LEPIDOPTERA. Those which have four membranaceous wings covered with
fine scales, appearing to the naked eye like powder or meal, as in the
butterfly and moth.
4. NEUROPTERA. These have four membranaceous transparent wings, which
are generally reticulated, the tail without a sting, as in the
libellula, or dragon fly.
5. HYMENOPTERA. These, like the preceding class, have four membranaceous
naked wings; but the abdomen is furnished with a sting, as in the bee,
wasp, ichneumon, &c.
6. DIPTERA. These have only two wings, and are furnished with halteres,
or poisers, instead of under wings, as in the common house fly, gnat,
&c.
7. APTERA. These are distinguished by having no wings, as in the spider,
louse, acarus, &c.
OF THE TRANSFORMATION OF INSECTS.
Insects are farther distinguished from other animals by the wonderful
changes that all those of the winged species without exception, and some
which are destitute of wings, must pass through, before they arrive at
the perfection of their nature. Most animals retain, during their whole
life, the same form which they receive at their birth; but insects go
through wonderful exterior and interior changes, insomuch that the same
individual, at its birth and middle state, differs essentially from that
under which it appears when arrived at a state of maturity; and this
difference is not confined to marks, colour, or texture, but is extended
to their form, proportion, motion, organs, and habits of life.
The ancient writers on natural history were not unacquainted with these
transformations, but the ideas they entertained of them were very
imperfect and often erroneous. The changes are produced in so sudden a
manner, that they seem like the metamorphoses recorded in the fables of
the ancients, and it is not improbable that those fables owe their
origin to the transformation of insects. It was not till towards the
latter end of the last century that any just conception of this subject
was formed; the mystery was then unveiled by those two great anatomists
Malpighi and Swammerdam, who observed these insects under every
appearance, and traced them through all their forms; by dissecting them
at the time just preceding their changes, they were enabled to prove
that the moth and butterfly grow and strengthen themselves, that their
members are formed and unfolded under the figure of the insect we call
a caterpillar, and that the growth was effected by a developement of
parts; they also shewed that it is not difficult to exhibit in these all
the parts of the future moth, as its wings, legs, antennæ, &c. and
consequently that the changes which are apparently sudden to our eyes,
are gradually formed under the skin of the animal, and only appear
sudden to us, because the insect then gets rid of a case which had
before concealed its real members. By this case it is preserved from
injuries, till its wings, and every other part of its delicate frame are
in a condition to bear the impulse of the sun, and the action of the air
naked; when all the parts are grown firm, and ready to perform their
several offices, the perfect animal appears in the form of its parent.
Though these discoveries dissipated the false wonders of the
metamorphoses that the world before believed, they created a fund of
real admiration by the discovery of the truth. These transformations
clearly prove, that without experience every thing in nature would
appear a mystery; so much so, that a person unacquainted with the
transformation of the caterpillar to the chrysalis, and of this to the
fly, would consider them as three distinct species; for who, by the mere
light of nature, or the powers of reason unaided by experience, could
believe that a butterfly, adorned with four beautiful wings, furnished
with a long spiral proboscis or tongue, instead of a mouth, and with six
legs, proceeded from a disgusting hairy caterpillar, provided with jaws
and teeth, and fourteen feet? Without experience, who could imagine that
a long white smooth soft worm hid under the earth, should be transformed
into a black crustaceous beetle? Nor could any one, from considering
them in their perfect state, have discovered the relation which they
bear to the several changes of state, and their corresponding forms,
through which they have passed, and which are to appearance as distinct
as difference can make them.
The life of those insects which pass through these various changes, may
be divided into four principal parts, each of which will be found truly
worthy of the utmost attention of the microscopic observer.
The first change is from the EGG into the LARVA, or, as it is more
generally called, into the worm or caterpillar. From the LARVA, it
passes into the PUPA, or chrysalis state. From the PUPA, into the IMAGO,
or fly state.
Few subjects can be found that are more expressive of the extensive
goodness of Divine Providence, than these transformations, in which we
find the occasional and temporary parts and organs of these little
animals suited and adapted with the most minute exactness to the
immediate manner and convenience of their existence; which again are
shifted and changed, upon the insects commencing a new scene and state
of action. In its larva state the insect appears groveling, heavy, and
voracious, in the form of a worm, with a long body composed of
successive rings; crawling along by the assistance of these, or small
little hooks, which are placed on the side of the body. Its head is
armed with strong jaws, its eyes smooth, entirely deprived of sex, the
blood circulating from the hind part towards the head. It breathes
through small apertures, which are situated on each side of the body, or
through one or more tubes placed in the hinder part thereof. While it is
in the larva state, the insect is as it were masked, and its true
appearance concealed; for under this mask the more perfect form is
hidden from the human eye. In the pupa, or chrysalis state, the insect
may be compared to a child in swaddling cloathes; its members are all
folded together under the breast, and inclosed within one or more
coverings, remaining there without motion. While in this state, no
insects but those of the hemiptera class, take any nourishment. The
change is effected various ways; in some insects the skin of the larva
opens, and leaves a passage, with all its integuments; in others, the
skin hardens and becomes a species of cone, which entirely conceals the
insect; others form or spin cones for themselves, and in this state they
remain till the parts have acquired sufficient firmness, and are ready
to perform their several offices.
The insect then casts off the spoils of its former state, wakes from a
death-like inactivity, breaks as it were the inclosures of the tomb,
throws off the dusky shroud, and appears in its imago or perfect form;
for it has now attained the state of organical perfection, which answers
to the rank it is to hold in the corporeal world: the structure of the
body, the alimentary organs, and those of motion, are materially
changed. It is now furnished with wings magnificently adorned, soars
above and despises its former pursuits, wafts the soft air, chooses its
mate, and transmits its nature to a succeeding race. Those members,
which in the preceding state were wrapped up, soft, and motionless, now
display themselves, grow strong, and are put in exercise. The interior
changes are as considerable as those of the exterior form, and that in
proportion as the first state differs from the last; some organs acquire
greater strength and firmness, others are rendered more delicate; some
are suppressed, and some unfolded, which did not seem to exist in the
former stages of its life.
OF THE LARVA STATE OF INSECTS.
As the larvæ or caterpillars of the moth and butterfly[63] form the most
numerous family among the tribe of insects, I shall first describe
them, and their various changes from this state to their last and
perfect form, and then proceed to those insects which differ most from
the caterpillar in one or all of their various changes.
[63] Butterflies are distinguished from moths by the time of their
flying abroad, and by their antennæ; the butterflies appear by day,
their antennæ are generally terminated by a little knob; the moths fly
mostly in the evening, and their antennæ are either setaceous or
pectinated.
The greater part of those insects which come forth in spring or summer,
perish or disappear at the approach of winter; there are very few, the
period of whose life exceeds that of a year; some survive the rigours of
winter, being concealed and buried under ground; many are hid in the
bark of trees, and others in the chinks of old walls; some, like the
caterpillar of the brown-tailed moth,[64] at the approach of winter not
only secure and strengthen the web in which the society inhabit, and
thus protect themselves from impertinent intruders, but each individual
also spins a case for itself, where it rests in torpid security,
notwithstanding the inclemency of the season, till the spring animates
it afresh, and informs it, that the all-bountiful Author of nature has
provided food convenient for it. Many that are hatched in the autumn
retire and live under the earth during the winter months, but in the
spring come out, feed, and proceed onward to their several changes;
while no small part pass the colder months in their chrysalis or pupa
state: but the greater number of the caterpillar race remain in the egg,
being carefully deposited by the parent fly in those places where they
will be hatched with the greatest safety and success; in this state the
latent principle of life is preserved till the genial influences of the
spring call it into action, and bring forth the young insect to share
the banquet that nature has provided.
[64] This moth was uncommonly numerous and destructive near London in
the year 1782, and, aided by the predictions of an empirical imposter,
occasioned a considerable alarm in the minds of the ignorant and
superstitious. The judicious publication of a short history of the
insect, by Mr. Curtis, in some measure contributed to dissipate their
fears. EDIT.
All caterpillars are hatched from the egg, and when they first proceed
from it are generally small and feeble, but grow in strength as they
increase in size. The body is divided into twelve rings; the head is
connected with the first, and is hard and crustaceous. No caterpillar of
the moth or butterfly has less than eight, or more than sixteen feet;
the six first are crustaceous, pointed, and fixed to the three first
rings of the body; these feet are the covering to the six future feet of
the moth; the other six feet are soft and flexible or membranaceous;
they vary both in figure and number, and are proper only to the larva
state; with respect to their external figure, they are either smooth or
hairy, soft to the touch, or hard like shagreen, beautifully adorned
with a great variety of the most lively teints; on each side of the body
nine little oval holes are placed, which are generally considered as the
organs of respiration. There are on each side of the head of the
caterpillar five or six little black spots, which are supposed to be its
eyes. These creatures vary in size, from half an inch long to four and
five inches.
The caterpillar, whose life is one continued succession of changes,
often moults its skin before it attains its full growth; not one of them
arrives at perfection, without having cast its skin at least once or
twice. These changes are the more remarkable, because when the
caterpillar moults, it is not simply the skin that is changed; for we
find in the exuvia, the skull, the jaws, and all the exterior parts,
both scaly and membranaceous, which compose its upper and under lip, its
antennæ, palpi, and even those crustaceous pieces within the head, which
serve as a fixed basis to a number of muscles; we further find in the
exuvia, the spiracula, the claws, and sheaths of the anterior limbs, and
in general all that is visible of the caterpillar.