INSECTS
provender, enjoying for a while a new life free from the domestic routine that has bound them since the days of their infancy. But even their liberty has an ulterior purpose: the time is now approaching when their lives as caterpillars must end and the creatures must go through the mysteries of transformation, which, if successfully accomplished, will convert them into winged moths. It would clearly be most unwise for the caterpillars of a colony to undergo the period of their metamorphosis huddled in the remains of the tent, where some untoward event might bring destruction to them all. Nature has, therefore, implanted in the tent caterpillar a migratory urge, which now becomes active and leads the members of
Fig. 151. The cocoon of a tent caterpillar. (Natural size)
a family to scatter far and wide. About a week is allowed for the dispersal, and then, as each wanderer feels within the first warnings of approaching dissolution, it selects a suitable place for inclosing itself in a cocoon.
It is difficult to find many cocoons in the neighborhood where large numbers of caterpillars have dispersed, but such as may be recovered will be round among blades of grass, under ledges of fences, or in sheds and barns where they are not disturbed. The cocoon is a slender oval or almost spindle-shaped object, the larger ones being about an inch long and half an inch in width at the middle (Plate 14 E, Fig. 151). The structure is spun of white silk thread, but its walls are stiffened and colored by a yellowish substance infiltrated like starch through the meshes of the fabric.
In building the cocoon the caterpillar first spins a loose network of threads at the place selected, and then, using this for a support, weaves about itself the walls of the final
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