INSECTS
tion. Birds often poke holes in them with their bills and rip off sheets of silk which they carry away for nest-building purposes. The caterpillars do not even repair these damages. The rooms of the tent become filled with accumulations of frass, molted skins, and the shriveled bodies of dead caterpillars. The walls are discolored by rains which beat into the openings and soak through the refuse. Thus, what were shapely objects of glistening silk are transmuted into formless masses of dirty rags.
But the caterpillars, now in their finest dress, are oblivious of their sordid surroundings and sleep all day amidst these disgusting and apparently insanitary conditions. However, the life in the tents will soon be over; so it appears the caterpillars simply think, "What's the use?" But of course caterpillars do not think; they arrive at results by instinct, in this case by the lack of an instinct, for they have no impulse to keep the tents clean or in
Fig. 150. A tent caterpillar in the last stage of its growth, leaving the tree containing its nest by jumping from the end of a twig to the ground
repair when doing so would be energy wasted. Nature demands a practical reason for most things.
The tent life continues about a week after the last molt, and then the family begins to break up, the members leaving singly or in bands, but always as individuals without further concern for one another. Judging from their previous methodical habits, one would suppose that the caterpillars starting off on their journeys would simply go down the trunks of the trees and walk away. But no; once in their life they must have a dramatic moment. A caterpillar comes rushing out of a tent as if suddenly awakened from
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