50 



ENTOMOLOGY. 



encloses the muscles and internal organs, gives firm- 

 ness to tlie whole body, and, by metuis of its articu- 

 lations, the limbs, and different parts of the body, 

 perform their various motions. In many insects, 

 such as the crab, lobster, c.,the external covering is 

 very hard, and destitute of organization ; It is compos- 

 ed of a calcarious earth, mixed with a small quantity 

 of gelatine, formed by an exudation from the surface 

 of the body. As its great hardness would check the 

 growth of the animal, nature has provided a remedy ; 

 all of these crustaceous insects cast their shell annual- 

 Jy. The skin of most of the other insects is softer, and 

 organized, being formed of a number of thin mem- 

 branes, adhering closely to one another and putting 

 on the appearance of horn. It owes its greater soft- 

 ness to a larger proportion of gelatine. 



The muscles of insects consist of fibres formed of 

 fasciculi ; there are commonly but two muscles to 

 produce motion in any of their limbs, the one an 

 extensor, the other a flexor. These muscles are 

 commonly attached to a tendon, composed of a horny 

 substance, connected to the part which they are 

 destined to put in motion. In most insects, the 

 brain is situated a little above the oesophagus ; it 

 divides into two large branches, which surround the 

 oesophagus and unite again under it, from which 

 junction a whitish nervous cord proceeds, corre- 

 sponding to the spinal marrow of the superior 

 animals, which extends the whole length of the body, 

 forming in its course twelve or thirteen knots or 

 ganglions, from each of which small nerves proceed 

 to different parts of the body. 



Whether insects be endowed with any senses differ- 

 ent from those of the superior animals, cannot easily 

 be ascertained. It appears pretty evident, that they 

 possess vision, hearing, smell, and touch ; as to the 

 sense of taste, we are left to conjecture ; for we are 

 acquainted with no facts by which we can prove 

 that insects do or do not enjoy the sense of taste. 

 The eyes of insects are of two kinds ; the one com- 

 pound, composed of lenses, large, and only two in 

 number ; the other are small, smooth, and vary in 

 number from two to eight. The small lenses, which 

 form the compound eyes, are very numerous ; 8000 

 have, been counted in a common house fly, and 1700 

 in a butterfly. The far greater number of insects 

 have only two eyes ; but some have three, as the 

 scolopendra ; some four, as the gyrinus ; some six, as 

 scorpions ; some eight as spiders. The eyes of 

 insects are commonly immovable ; crabs, however, 

 have the power of moving their eyes. That insects 

 are endowed with the sense of hearing, can no longer 

 be disputed, since frog-hoppers, crickets, &c., furnish 

 us with undeniable proofs of the fact. Nature has 

 provided the males of these insects with the means 

 of calling their females, by an instrument fitted to 

 produce a sound which is heard by the latter. The 

 male and female death-watch give notice of each 

 other's presence, by repeatedly striking with their 

 mandibles against old wood, &c., their favourite 

 haunts. Their ears have been discovered to be placed 

 at the root of their antennae, and can be distinctly seen 

 in some of the larger kinds, as the lobster. The anten- 

 nae or feelers seem to be merely instruments of 

 feeling, though some naturalists have thought them 

 to be organs of tasting and smelling ; and others, of a 

 sense unknown to us. The amazing variety in the 

 mouths of insects, is evident from the feet, that their 

 whole classification, in the Fabrician system, is 

 founded on it. That insects enjoy the faculty of smell- 

 ing is very evident ; it is the most perfect of all their 

 senses. Beetles of various sorts the different species 

 of dermestes, flies, &c., perceive at a considerable 

 distance the smell of ordure and dead bodies, iind 

 resort in swarms to the situations in which they 



occur, either for the purpose of procuring food, or 

 laying their eggs. 



Insects feed on a great variety of substances ; 

 there are few things, either in the vegetable or 

 animal kingdom, which are not consumed by some 

 of them. The leaves, flowers, fruit, and even the 

 ligneous parts of vegetables, afford nourishment to a 

 very numerous class; animal bodies, both dead 

 and alive, even man himself, is preyed on by 

 many of them ; several species of the louse, of the 

 acarus, of the gnat, and the common flea, draw their 

 nourishment from the surface of his body ; the pulex 

 ulcerans penetrates the cuticle, and even enters his 

 flesh. A species of gadfly (oestrus hominis) deposits 

 its eggs under his skin, where the larvae feed. Other 

 caterpillars insinuate themselves into different cavi- 

 ties of his body. All the inferior animals have their 

 peculiar parasitical insects, which feed on them dur- 

 ing their life. There are some insects which can 

 feed only on one species. Many caterpillars, both 

 of moths and butterflies, feed on the leaves of some 

 particular vegetable, and would die, could they 

 not obtain this. There are others which can make use 

 of two or three kinds of vegetables, but which never 

 attain full perfection, except when they are fed on 

 one particular kind ; for example, the common silk- 

 worm eats readily all the species of mulberry, and 

 even common lettuce, but attains its greatest size, 

 and produces most silk, when fed on the white mul- 

 berry. There are a great many which feed indis- 

 criminately on a variety of vegetables. Almost all 

 herbivorous insects eat a great deal, and very fre- 

 quently ; and most of them perish, if deprived of 

 food but for a short time. Carnivorous insects can 

 live a long while without food, as the carabus, ditis- 

 cus, &c. 



As many insects cannot transport themselves 

 easily, in quest of food, to places at a distance from 

 one another, nature has furnished the perfect insects 

 of many species with an instinct, which leads them 

 to deposit their eggs in situations where the larvae, 

 as soon as hatched, may find that kind of food which 

 is best adapted to their nature. Most of the butter- 

 flies, though they flutter about, and collect the nec- 

 tareous juice of a variety of flowers, as food for 

 themselves, always deposit their eggs on or near to 

 those vegetables which are destined, by nature, to 

 become the food of their larvae. The various spe- 

 cies of ichneumon deposit their eggs in the bodies of 

 those insects on which their larvae feed. (See 

 Ichneumon.') The sirex and sphex are likewise 

 careful to deposit their eggs in situations where their 

 larvae, when hatched, may find subsistence. The 

 sphex figulus deposits its eggs on the bodies of spi- 

 ders which it has killed, and enclosed in a cell com- 

 posed of clay. Some insects, at different periods of 

 their existence, make use of aliment of very different 

 properties ; the larvae of some are carnivorous, while 

 the perfect insect feeds on the nectareous juice of 

 flowers, e. g. sirex, ichneumon, &c. The larvae of 

 most of the lepidopterous insects feed on the leaves 

 and young shoots of vegetables, while the perfect 

 insects either take no food at all, or subsist on the 

 sweet juice which they extract from flowers : indeed, 

 the construction of their mouths prevents them from 

 taking any other than fluid food. 



We shall now refer to the functions of insects 

 beginning with respiration, which is the act of inhal- 

 ing and exhaling the air into and out of the lungs. 

 Mammalia, birds, and most of the amphibia, breathe 

 through the mouth and nostrils. The air, when 

 received into the lungs, is mixed with the blood, and 

 imparts to it something necessary, and carries off 

 something noxious. Some authors have asserted 

 that insects have no lungs; but later experiments 



