146 LEAF-MINING INSECTS 



and lined it with a thin sheet of silk, the larva go to the end 

 of the mine towards the base of the leaf and sever the mined 

 from the unmined portion. They then thrust forth head 

 and legs and travel about wearing the modified burrow as a 

 protecting case. For three or four weeks in the fall they 

 continue to feed. They now attach the rounded mouth of 

 the case to the needles with silk, pierce the cuticle and de- 

 vour the leaf substance as far as they can reach in either 

 direction. While working from the cases the larvae back 

 up from time to time, and, thrusting the anal segment 

 through the posterior opening of the case, void their excre- 

 ment. When the larvae can obtain no more food without 

 leaving the case entirely they sever their moorings, move to 

 another leaf and proceed as before. Each larva may mine 

 thoroughly more than one leaf after forming its case and 

 before going into hibernation but unless the insects are 

 exceedingly numerous, their work is inconspicuous at this 

 season. 



In October they cease to feed and, shortly before the 

 needles drop, move to the branches. There, often in the 

 axil of a bud, they fasten their cases with a copious supply 

 of silk, close the anal opening with a sheet of silk and become 

 inactive. Though the larch needles are flat the clustered 

 or separated cases are cylindrical, the lining of silk and the 

 shape and activity of the larvae having caused the bulging 

 of the flat surfaces. The larvae at this time have reached a 

 fourth to a third of their ultimate size and are much smaller 

 than their cases in which they can turn and twist about 

 with ease. The cases are an eighth to a sixth of an inch in 

 length. 



In the spring when the larch buds begin to swell the larvae 

 awake from their long sleep enhungered; so, loosening them- 

 selves from the branches, they at once burrow into the 

 young leaves. Back on the twigs, where the cases are 



