312 Gardening 
often completely strip the leaves of young plants, check- 
ing their growth and preventing the proper formation of 
Fic. 174. Different stages in the life of the cabbage butterfly. 
heads. On older plants they burrow from leaf to leaf 
among the outer leaves of a head, leaving castings that 
make the heads undesirable as food. The caterpillar in- 
creases in size, shedding or molting its skin several 
times as it grows, until in 2 or 3 weeks it is an inch or 
more long. 
When fully grown, a caterpillar attaches itself firmly 
by a few silken threads, sheds its skin again, and in- 
closes itself in a thin but tough and horny covering. It 
