INSECTS IN GENERAL. 



437 



an attentive examination," says Swammer- 

 dam, "of the nature and anatomy of the 

 smallest as well as the largest animals, I can- 

 not help allowing the least an equal, or, per- 



the other hand, they are provided with an incalculable 

 number of air-vessels of an astonishingly delicate struc- 

 ture, and with numerous muscles, differing, however, as 

 well in form as in colour, from those of red-blooded ani- 

 mals. 



Although insects stand in need of the exchange of 

 carbon of oxygen to effect the continuance for life, there 

 are but few, as crabs, grasshoppers, many cicada; and 

 chafers, in which a motion resembling respiration can be 

 observed. Insects in general breathe, not by the mouth, 

 but by many spiracula *. The greater number of them 

 can live in a vacuum much longer than red-blooded 

 animals, and many in mephitic atmospheres so fatal to 

 others, and in which animal and vegetable substances 

 become putrid, as carburetted hydrogen gas, &c. 



The abode of insects on and under the surface of the 

 earth, is much less limited than that of the other classes 

 uf animals. They are found on almost all warm-blooded 

 animals, and even the larger insects, as bees, chafers, 

 &c., are infested by peculiar kinds of lice. There are but 

 few plants, also, (such as perhaps, the yew, savine, and 

 most tree-mosses,) which do not serve for the abode and 

 support of known insects. Many again, as the oak, are 

 frequented and inhabited by more than a hundred dis- 

 tinct species. Generally, however, as insects are diffused 

 over the earth, the residence of individual species is not 

 less frequently limited to a very small number of ani- 

 mals and plants, or even particular parts of them. 



Only a few insects live in a social state, affording 

 mutual assistance in their labours. The greater number 

 follow their pursuits singly : many, as spiders, live in 

 society when young, but afterwards separate and live in 

 a state of solitude, seeing creatures of the same species 

 only at the time of pairing. 



The remarkable edifices and habitations, which so 

 many insects are capable of executing, have been already 

 mentioned in speaking of instinct. There are but few 

 creatures of this class which do not, at least onc in their 

 life, give proofs of this natural power of construction ; 

 either, as the cloth-moth and water-moth, form a habita- 

 tion in their complete and larva state ; or, like others, 

 spin and prepare a receptacle to contain them during 

 their metamorphosis and death. like sleep ; or like the 

 lion-ant, dig pits ; and like the spider, weave webs for 

 their prey ; or like many species of the genus Dyticus, 

 and some spiders, form bags or nets for the security of 

 their posterity, and in which they deposit their eggs. 

 Many of those which live in communities, build common 

 residences, by their united powers, and under the 

 guidance of an extremely regular, geometrical, innate 

 instinct. 



As to the kind of nourishment in insects, it is easy to 

 see that it is not, as in most red-blooded animals, calcu- 

 lated merely for the preservation of the individual, but 

 more particularly for the purpose of consuming organized 

 matter. Insects must eat, not solely to satisfy hunger, 

 but also to destroy carrion, to annihilate other insects, to 

 extirpate weeds, &c. An admirable provision, to the 

 execution of which, besides the almost incalculable num- 

 ber of species, the extremely rapid multiplication of 

 many, the unexampled voracity of others, and the quick- 

 ness with which digestion is carried on in their very 

 short intestinal canal, all tend to contribute. Thus it is 

 known that a caterpillar will in twenty-four hours con- 



* On the other liand, this class, in proportion to its vast 

 number of species, contains but few aquatic animals : and of 

 these, but very few exist in the oc-ean, which forms the abode 

 or by far the greater number of species in the preceding and 

 succeeding classes. 



haps, a superior degree of dignity. If, while 

 we dissect with care the largest animals, we 

 are filled with wonder at the elegant disposi- 

 tion of their parts ; to what a height is our 



stime more than three times its own weight. The organs 

 of mastication in insects are more diversified than in any 

 other class of animals : many are provided with jaws, 

 having teeth and moving laterally : others, with a horny, 

 pointed snout, (rostrum) for boring; others with a 

 fleshy snout having a wide opening, (proboscis} ; and 

 others with a tongue, so called, rolled into a spiral shape. 



Some insects are secured from the attacks of their 

 enemies by their deceptive form ; others by having the 

 same colour as the plants on which they live, and con- 

 sequently being Jess readily noticed ; others, by the 

 powerful smell which they can diffuse in case of neces- 

 sity; others by their social mode of life ; others again by 

 their astonishing strength, &c. Many are provided 

 with weapons, as horns like forceps or nippers, or with 

 stings and venom. 



In the mode of propagation of insects there are also 

 many peculiarities. Thus the two sexes in one and the 

 same species are often so extremely different in form 

 that they seem like animals of distinct kinds: in bee?, 

 and many similar insects, the greater number is without 

 sex ; that is to say, they are themselves produced with- 

 out being destined in the ordinary course of nature for 

 generation or impregnation. 



This peculiarity extends in different insects to the 

 mode of copulation. In not a few species, for instance, 

 it is effected in flying, and many possess wings only 

 during the short season of breeding. In general, the 

 greater number live in a state of compulsory monogamy, 

 inasmuch as they are incapable of copulating more than 

 once in the course of life : death is with them so 

 inevitable a result of their first copulation, that life may 

 be prolonged by delaying the period of sexual connec- 

 tion. 



Among other peculiarities of the business of propa- 

 gation in insects, many, as the cochineal-worm, the 

 land-flea, become of an enormous size during pregnancy: 

 thus, in the white aut, it has been calculated that the 

 abdomen of the female, when about to lay her eggs, is 

 2000 times larger than previous to impregnation. 



Most insects lay eggs, which the mother, by a truly 

 wonderful instinct, always deposits precisely in the situa- 

 tions best adapted for the future progeny. Many, for in- 

 stance, lay their eggs in the bodies of living insects of 

 other kinds, as in caterpillars, pupae, &c. ; or even in the 

 eggs of other kinds of insects. The eggs of insects are 

 occasionally, particularly among butterflies, of very vari- 

 ous and remarkable form and appearance, and when de- 

 posited by the mother in the open air, are covered with 

 a kind of varnish, protecting them from the des- 

 tructive influence of rain and other accidents. Some few 

 insects are viviparous, and many, as the plant-lice 

 (Aphides), propagate in both ways. 



A very remarkable phenomenon, almost confined to 

 this class of animals, or at least much less striking in the 

 others, is their metamorphosis. There is not any winged 

 insect which escapes from the egg as such, but al), as 

 well as many insects which have not wings, must firs! 

 undergo a kind of change at certain periods of their ex- 

 istence. By this, not only their external form, but also 

 at the same time their internal structure, contrary to com- 

 mon opinion, is altered in a certain degree, a circum- 

 stance which by no means coincides with the supposed 

 pre-existence of pre-formed germs. 



If the moth existed already formed in .the caterpillar, 

 we should at least expect that similar moths should be 

 produced by similar caterpillars. But many American 

 caterpillars, which resemble European ones in the closest 

 mannerpossible, give origin to moths having totally clif- 



