HYMENOPTERA. 3S5 



next spring, exhausts the vigor of the trees, and cuts off the 

 prospect of fruit. The slug-worms come to their growth in 

 twenty-six days, during which period they cast their skins five 

 times. Frequently, as soon as the skin is shed, they are seen 

 feeding upon it ; hut they never touch the last coat, which re- 

 mains stretched out upon the leaf. After this is cast off, they no 

 longer retain their slimy appearance and olive color, hut 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 in their cocoons, 

 and it is probable that birds also prey upon them when on the 

 trees, both in the slug and the winged states. Professor Peck 

 has described a minute ichneumon-fly, stated by Mr. Westwood 



49 



