MONTANA EXPERIMENT STATION. 147 



hatchins^ the black head and thoracic shield of the larvae show- 

 through distinctly. A number of eggs were carefully marked by 

 means of bits of paper, string etc. and a weighted average of ii days 

 was obtained as the length of this stage. In laying the eggs the 

 moths avoided almost entirely the branch of the tree sprayed on 

 May 25th which still retained a considerable coating of the poison. 

 The first of the larvae began to appear on June 11 and by the 20th 

 the insect was practically again in this stage. When free from 

 the egg the minute larvae proceed at once to the under side of the 

 leaves and begin to feed along the mid-rib or some of its larger 

 branches. Usually they burrow down between the upper and low- 

 er skins of the leaf feeding and at the same time covering them- 

 selves over with frass and the pubescence of the leaves, which they 

 weave into a solid mass by the use of their spinnerets and ever 

 ready supply of silk. At no time in its existence as a larva is the 

 msect without this string of silk, and wherever it is the end of this 

 life line is always anchored securely. They have been seen to drop 

 a distance of 3 or 4 feet before being stopped by this minute thread, 

 and after waiting a moment for the intruder to leave wriggle back 

 by a whirling motion to the place of attachment. With the 3'ounger 

 lighter larvae this is a simple task but the heavy-bodied adult often 

 breaks its life line and drops. When affected b}^ poison the worm 

 often neglects, or is unable to attach its thread and while throwing 

 itself about blindly will often fall to the ground. At first the Min- 

 iature grub feeds very slowly and it is some time before the feeding 

 grounds are enlarged to any considerable extent. During this time 

 the larvae are so closel}' covered by their cocoons and hidden behind 

 the leaf veins that they are practically immune from spray o. an}' 

 kind. After about 14 days however they begin again to have a 

 definite routine, making nightly rounds from their cdcckjus tt) the 

 more distant parts of the leaves. As they grow and extend their 

 ravages they are of course more unprotected and feed upon a great- 

 tr per cent of the exposed cuticle. At about this time the grubs ap- 

 parently foresee a need of extra supplies and as their habitats wither 

 they begin to stick other leaves to them. This is done very skill- 

 fully and cleverly ; the flat surfaces of the leaves are fastened to- 

 gether and the worms feed within, free from any possible invader. 

 At the first indications of this propensity it was seen that the leaves 



