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 hist 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 tbe 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 deptli of from one inch to three or four 
inches, according to the nature of the soil. Bv 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 eartb 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 
