THE PEAR-TREE SLUG. 531 



The slug-worms come to their growth in twenty-six days, 

 during which period they cast their skins five times. Fre- 

 quently, as soon as the skin is shed, they are seen feeding 

 upon it ; but they never touch the last coat, which remains 

 stretched out upon the leaf. After this is cast off, they 

 no longer retain their slimy appearance and olive color, 

 but have a clean yellow skin, entirely free from viscidity. 

 They change also in form, and become proportionally longer; 

 and their head and the marks between the rings are plainly 

 to be seen. In a few hours after this change, they leave 

 the trees, and, having crept or fallen to the ground, they 

 burrow to the depth of from one inch to three or four 

 inches, according to the nature of the soil. By moving 

 their body, the earth around them becomes pressed equally 

 on all sides, and an oblong oval cavity is thus formed, and 

 is afterwards lined with a sticky and glossy substance, to 

 which the grains of earth closely adhere. Within these 

 little earthen cells or cocoons the change to chrysalids 

 takes place; and, in sixteen days after the descent of the 

 slug-worms, they finish their transformations, break open 

 their cells, and crawl to the surface of the ground, where 

 they appear in the fly form. These flies usually come forth 

 between the middle of July and the first of August, and 

 lay their eggs for a second brood of slug-worms. The 

 latter come to their growth, and go into the ground, in 

 September and October, and remain there till the following 

 spring, when they are changed to flies, and leave their 

 winter quarters. It seems that all of them, however, do 

 not finish their transformations at this time ; some are found 

 to remain unchanged in the ground till the. following year; 

 so that, if all the slugs of the last hatch in any one year 

 should happen to be destroyed, enough from a former brood 

 would still remain in the earth to continue the species. 



The disgusting appearance and smell of these slug-worms 

 do not protect them from the attacks of various enemies. 

 Mice and other burrowing animals destroy many of them 

 67* 



