The labours of those insect-architects, which we have endeavoured to describe in the preceding pages, have been chiefly those of mothers to form a secure nest for their eggs, and the young hatched from them, during the first stage of their existence. But a much more numerous and not less ingenious class of architects may be found among the newly-hatched insects themselves, who, untaught by experience, and altogether unassisted by previous example, manifest the most marvellous skill in the construction of tents, houses, galleries, covert-ways, fortifications, and even cities, not to speak of subterranean caverns and subaqueous apartments, which no human art could rival. The caterpillars, which are familiarly termed leaf-rollers, are perfect hermits. Each lives in a cell, which it begins to construct almost immediately after it is hatched; and the little structure is at once a house which protects the caterpillar from its enemies, and a store of food for its subsistence, while it remains shut up in its prison. But the insect only devours the inner folds. The art which these caterpillars exercise, although called into action but once, perhaps, in their lives, is perfect. They accomplish their purpose with a mechanical skill, which is remarkable for its simplicity and unerring success. The art of rolling leaves into a secure and immovable cell may not appear very difficult: nor would it be so if the caterpillars had fingers, or any parts which were equivalent to those delicate and admirable natural instruments with which man accomplishes his most elaborate works. And yet the human fingers could not roll a rocket-case of paper more regularly than the caterpillar rolls his house of leaves. A leaf is not a very easy substance to roll. In some trees it is very brittle. It has also a natural elasticity,--a disposition to spring back if it be bent,--which is caused by the continuity of its threads, or nervures. This elasticity is speedily overcome by the ingenuity with which the caterpillar works; and the leaf is thus retained in its artificial position for many weeks, under every variety of temperature. We will examine, in detail, how these little leaf-rollers accomplish their task. One of the most common as well as the most simple fabrics constructed by caterpillars, may be discovered during summer on almost every kind of bush and tree. We shall take as examples those which are found on the lilac and on the oak. [Illustration: Lilac-tree Moth. (_Lozotænia riteana_, Stephens?)] [Illustration: Nest of a Lilac-leaf Roller.]