ason 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 develop more
quickly than those which have to live on dry, poor, substances;
life-cycles follow one another most rapidly in summer weather when
temperature is high and food plentiful.

In early chapters we have already noticed the long aquatic life of the
larva and nymph of a dragon-fly, relatively a large insect, and the
rapid multiplication of the repeated summer broods of virgin aphids (p.
18). Within the one order of the Coleoptera it is instructive to compare
the small jumping leaf-beetles, the 'turnip-flies' of the farmer, whose
larvae mine in the green tissues, and complete their transformations so
rapidly that several successive 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 few days.
As examples of excessively long life-cycles the 'thirteen-year' and
'seventeen-year' cicads of North America, described by C.L. Marlatt
(1895), are noteworthy. Certain specially populous 'broods' of these
insects are known and localised, so that the appearance of the imagos in
future years can be accurately predicted. Here again we have to do with
bulky insects whose subterranean larvae and nymphs feed on comparatively
innutritious roots.

In our own climate, it is of interest to notice the variation among
insects as to the stage which carries the race over the winter. The
click-beetles, mentioned just above, emerge from their buried pupae in
summer, hibernate under stones or clods, and lay eggs among the herbage
next spring. At the same time of course, owing to the extended term of
the larval life, many more individuals of 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 th