The Life-Story of Insects

aquatic life of the larval dragon-fly or may-fly, extending over several years, and the short aerial existence of the winged adult restricted in the case of the may-flies to a few hours. Here we see

gain in many moths the jaws are reduced or vestigial so that no food can be taken in the winged state, as for example in the 'Eggars' (Lasiocampidae) and the 'Tussocks' (Lymantriidae). It is noteworthy that in these short-lived insects the male is often provided with elaborate sense-organs which, we may believe, assist him to find a mate with as little delay as possible; the male m

ge only is omitted from the life-history. Not always however is it the imaginal stage of the life-history which is shortened. Reference (p. 18) has already been made to the case of the virgin female aphids, whose eggs develop within the mother's body, so that active, formed young are brought forth. Among the Diptera it is not unusual to find similar cases, the female fly giving birth to young maggots instead of laying eggs. Such is the habit of the great flesh-fly (Sarcophaga), of some allied genera (Tachina, etc.) whose larvae live as parasites on other insects, and occasionally of the Sheep Bot-fly (Oestrus). In such cases we recognise the beginning of a shortened larval period, and Brace's investigations in 1895, summarised by E. E. Austen (1911), have shown that females of the dreaded African Tsetse flies (Glossinia) bring forth nearly mature larva

, its food, the season of the year when it breeds. Small insects have, as a rule, shorter lives than large ones; those whose larvae devour highly nutritive food generally develo

cessive broods appear in the spring and early summer, with the larger click-beetles whose larvae, the equally notorious 'wireworms,' feed on roots for three or four years before they become fully grown. Among the Diptera, the 'leather-jacket' grub of the crane-fly, feeding like the wireworm on roots, has a larval life extending through the greater part of a year, while the maggot of the bluebottle, feeding on a rich meat diet, becomes mature in a f

the species are wintering underground as 'wireworms' of various ages, and these, except in very severe frosts, can continue their occupation of feeding on roots. But in the case of the 'turnip-flies' the food-supply is cut off in winter, and all those beetles of the latest summer brood that survive hibernate in some sheltered spot, waiting for the return of spring, that they may lay their

by grubs, which after pupation develop into winged males and wingless females. The latter, after pairing, burrow underground and lay their eggs in the roots, the larvae causing the presence there of globular swellings or root-galls within which they live, pass through their transfo

mple, undergo a development extending over several years, while at the other extreme a few small species may have three or more complete cycles within the twelve months. Bu

aves of their caterpillars' food-plants. The larvae feed and grow through the early summer months, in the case of the Small Tortoiseshell (Vanessa urticae) pupating before midsummer and developing into a July brood of butterflies whose offspring after a late summer life-cycle, hibernate; while for the larger species of the group there is, in our islands, only one complete life-cycle in the year, though the same insects in warmer countries may be double-brooded. C. G. Barrett records (1893, vol. I. pp. 153-4) how in the August of 1879 hundreds and thousands of 'Painted Ladies' (Pyrameis car

ed. After pairing, the female lays her eggs among the silk of the cocoon, partly covering them with hairs shed from her body, and then dies. The eggs thus protected remain through the winter, the larvae not being hatched till springtide, when the young leaves begin to sprout forth. The caterpillars, adorned and probably protected by their 'tussocks' of black or coloured bristles, feed vigorously. Their activity

these, instead of beginning to feed, seek almost at once for rolled-up leaves, cracks in walls, crannies of bark, or similar places, which may afford winter shelters. Here they remain until the spring, when they come out to feed on the young foliage and grow rapidly into the conspicu

ety of plants. The larvae hatched from these eggs begin to feed at once, and having moulted once or twice and attained about half their full size, they rest through the winter, the dense hairy covering wherewith they are provided forming an effective protection ag

und by night, biting off the farmer's ripening corn, or burrowing into his turnips or potatoes. On account of the burrowing habits of this insect it can feed throughout the winter, except when a hard frost puts a temporary stop to its activity. By April it has become fully grown and pupates in an earthen chamber a few inches below the surface. The Turn

hich however the caterpillar always bores by the upper (calyx) end. Here it feeds, growing with the growth of the fruit, feeding on the tissue around the cores, ultimately eating its way out through a lateral hole, and crawling upwards if its apple-habitation has fallen, downwards if it still remains on the bough, to shelter under a loose piece of bark where it spins its cocoon about midsummer and hibernates still in the larval condition. Not until spring is the pupal form assumed, and then i

ies on the wing in late April or May is hailed as a sign of advanced spring-time. They pair and lay their eggs on cabbages and other plants, and the green hairy caterpillars feed in June and July, after which the spotted pupae may be found on fences and walls, attached by the silken tail-pad and supported by the waist-girdle. In August and September butterflies of the second broo

winters in the egg, the magpie as a young ungrown larva, the 'tiger' as a half-size larva; the Agrotis caterpillar feeds through the winter, growing all the time; the codling caterpillar completes its growth in the

ter, he succeeded in completely changing every individual of the summer generation into the winter form. The reverse of this experiment also was attempted by Weismann. He took a female of bryoniae, an alpine and arctic variety of Pieris napi, showing in an intensive degree the characters of the spring brood. This female laid eggs the caterpillars from which fed and pupated. The pupae although kept through the summer in a hothouse all produced typical bryoniae, and none of these with one exception appeared until the next year, for in the alpine and arctic regions this species is only single-brooded. Weismann experimented also with a small vanessid butterfly, Araschnia levana, common on the European continent, though unknown in our islands, which is double (or at times treble) brooded, its spring form (levana) alternating with a larger and more brightly coloured summer form (prorsa). Here again by refrigerating the summer pupae, butterflies were reared most of which approached the winter pattern, but it was impossible by heating the winter pupae to change levana into prorsa. Experiments with North American dimorphic species have given similar results. Weismann argued from these experiments that the winter form o

s various stages is plastic, open to influence from its surroundings, capable of marked change in the course of generations. And