Page:The American Cyclopædia (1879) Volume IX.djvu/325

INSECTS 313 larval condition persists sometimes for several months, as from the autumn to the following summer, and in the case of the harvest fly for a much longer period. Larva? are gener- ally voracious and active, but nymphs are as generally motionless and do not eat; some- times the larval skin hardens into a shell-like covering for the nymph ; at others a thin in- vesting pellicle applied to the body permits the animal to be seen through it. Before undergo- ing this change the larva often prepares a shel- ter, making a cocoon of silk secreted by itself ; the nymph may be suspended from a twig by silken filaments or concealed in some crevice. In the nymph state growth takes place rapidly, and the form of the future insect is gradual- ly assumed. The metamorphoses are easily studied in the common caterpillars, the bee, the mosquito, the fly, and the silkworm. The life of the perfect insect is short, enduring at most for the summer months, until the work of reproduction is completed ; in the ephemera the adult state continues for a few hours only. As instances of incomplete metamorphosis may be mentioned the cockroach, the cricket, the grasshopper, and other orthoptera, in which the larva differs from the perfect insect princi- pally in the absence of wings. For further de- tails on larvae and pupee, the reader is referred to CATERPILLAR, CHRYSALIS, and the various insects in their respective order. As insects furnish food for a great variety of vertebrate and invertebrate animals, their extermination would ensue were it not for their astonishing fecundity, paralleled only in the case of fishes ; a female termes (ant) has been estimated to lay about 90,000 eggs in a day ; the queen bee deposits between 5,000 and 6,000, the common ant about 1,000 less, the wasp about 3,000 ; a posterity of 1,000 in one generation is com- mon ; in the silkworm the average is 500 ; the beetles are far less prolific. Reaumur observed 350 young ones developed from the numerous eggs of a moth (phalana), many of which died as caterpillars, so that only 65 females reached the perfect state ; these were calculated to pro- duce the following year 22,750, which in the next would produce 1,500,000. A single plant louse (aphig), which brings forth a numerous progeny, but only one at a time, according to the above author's calculation, would produce in the fifth generation about 6,000,000,000, the great-great-grandmother laying eggs when the ninth member of her descendants is capable of reproduction, without contact with the male. The muscular activity of insects is very great, whether in leaping, swimming, flying, digging, or carrying weights ; no mammal can leap in proportion so high or so far as the flea, to a distance more than 200 times the length of its own body ; no bird has a facility of motion, and a rapidity and endurance of flight, com- parable to those of insects. The wings of the butterfly have been found to display the struc- ture ascertained by civil engineers to com- bine the greatest lightness with the greatesl strength ; in the nervure of the wing, as in the strongest beam, the utmost possible material .s thrown into the flanges, and the upright support is as thin as practicable; in the hol- ow nervures we have two flanges connected Dy the thin membrane of the wing, and the strongest nervure at or near the anterior edge. The apparatus by which many insects walk upon perpendicular surfaces is described in the article FLY. The larva of the ant lion digs its sand pit, and the fossorial wasp a hole for its eggs, in a very short time ; a few ants are strong enough to drag from their hill a large caterpillar ; a few burying beetles will place a mole under the earth in an hour, a feat equiva- lent to as many men burying a large whale in the same space of time ; the gadfly is faster than the fleetest horse ; a humblebee has been known to distance a locomotive going at the rate of 20 miles an hour, and a dragon fly to lead a swallow a weary chase of an hour, and at last escape. The instincts of insects, which sometimes closely border upon intelligence, are very remarkable, and calculated to excite the admiration of the most superficial observer. Insects apparently acquire knowledge from ex- perience, possess the faculty of memory, and are able to communicate their purposes to their fellows; they evince great sagacity in their methods of procuring food and in defending themselves against their enemies ; their de- vices for entrapping prey are very ingenious : to escape their enemies, some feign death, and others conceal themselves, fight bravely with their jaws and stings, and emit a nauseous odor or corrosive juices. As examples of insect in- stincts we need only mention those of the bee, wasp, and ant in constructing their habita- tions, of the silkworm, of the caterpillars (like tortrix and the clothes moth) which roll up leaves or woolly materials for their protection, of insects which unite in communities for mutual protection and support, and of those which lay their eggs on substances most proper for their young, which they will never see, and which feed on matters entirely different from the food of their parents (as the wasps). In their adaptation of these instincts to acci- dental circumstances, they approach very near to intelligent acts. Insects have many pas- sive means of avoiding their enemies in the form and structure of their bodies, and in their resemblance in color to the objects on which they live, whether ground or tree, as in beetles, grasshoppers, the mantis, and many bugs living on bark ; the larvfe of tortoise beetles are spiny, others are hairy, and con- sequently avoided by insectivorous birds; hardness of integument and tenacity of life are also important means of preservation. The continuance of the species is secured by the strong sexual impulse, and by the care of the female in depositing her eggs in' plnces where the future welfare of the young will be in- sured; the life of the insect generally ceases soon after the period of sexual activity;