ey may lay
their eggs, and start the life-cycle once again. Among the Diptera, most
species pass the winter as pupae, the sheltering puparium being a good
protection against most adverse conditions, or as flies. But where there
is a prolonged parasitic larval life, as with the bot- and warble-flies,
the maggot, warm and well-fed within the body of its mammalian host,
affords an appropriate wintering stage.

Among the Hymenoptera an especially interesting seasonal life-cycle is
afforded by the alternation of summer and winter generations in many
Gall-flies (Cynipidae) as H. Adler (1881, 1896) demonstrated for most of
our common species. The well-known 'oak-apples' are tenanted in summer
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
transformations and develop into wingless virgin females. These shelter
until February or March in their underground chambers, then climb up
the tree and lay on the shoots eggs, from which will be hatched the
grubs destined to grow within the oak-apples into the summer sexual
brood of flies.

The Lepidoptera afford examples of hibernation in all stages of the
life-history. In this order a few large moths with wood-boring
caterpillars, the 'Goat' (Cossus) for example, 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.
But in the vast majority of Lepidoptera we find either one or two
generations, definitely seasonal, within the year; the insect is either
'single-brooded' or 'double-brooded.'

Almost every winter one or more letters may be read in some newspaper
recording the writer's surprise at seeing on a sunny day during the cold
season, one of our common gaily-coloured butterflies of the Vanessa
group, a 'Tortoiseshell' or 'Red Admiral,' flitting about. Surprise
might be greater did the observers realise that the imaginal is the
normal hibernating stage for these species. Emerging from the pupa in
late summer or autumn, they shelter during winter in hollow trees, under
thatched eaves, in outbuildings or in similar situations, coming out in
spring to lay their eggs on the leaves of their caterpillars'
food-plants. The larvae feed and grow through the ear