labvjE op saw-flies. 517 



legs than true caterpillars, being provided with from eighteen 

 to twenty-two ; but their prop-legs have not the numerous 

 little hooks that arm those of caterpillars. They have the 

 means of spinning silk from their lower lips, but not often 

 in any great quantity. They are mostly naked and without 

 hairs ; a few have forked prickles on their backs ; some 

 are covered with a white flaky substance, that easily rubs 

 off; and others have a dark-colored slimy skin, which has 

 caused them to be called slugs or slug- worms. They shed 

 their skins about four times, and, after the last moulting, 

 often materially change in appearance. Not only do these 

 insects resemble caterpillars in their forms, but they have 

 nearly the same habits. They are generally found on the 

 leaves of plants, which they devour. Many kinds are al- 

 together solitary ; a few live together in swarms, under silk- 

 en webs, which they spin for a common place of shelter; 

 others are found also in swarms, but without any webs over 

 them, and, when disturbed, they throw up their heads and 

 tails, in a very odd way ; some roll up leaves, and live in 

 the hollow thus formed, like the Tortrices ; others make 

 portable cases of bits of leaves, which they carry about on 

 their backs, like the Tinese ; certain kinds live within the 

 stems of plants, and devour the pith ; and wheat, in Europe, 

 is said to suffer considerable injury from internal feeders 

 (Cephus pygmceus) of this kind. When fully grown, most 

 of them go into the ground, and enclose themselves in thin 

 silken cocoons, of an oblong oval shape, coated with grains 

 of earth. Some make much thicker cocoons, in texture 

 resembling parchment, and fasten them to the plants on 

 which they live, or conceal them in crevices, or under leaves 

 and stones on the ground. They generally remain for a 

 long time unchanged in their cocoons, most of them during 

 the winter ; are transformed to chrysalids, of a whitish color, 

 in the spring, and come out in the winged form soon after- 

 wards. Of some kinds there are two broods in the course 

 of the summer, the false caterpillars of the first brood 



