THE CANADIAN ENTOMOLOGIST. ' 225 



two larvae are placed on the same leaf, one always takes possession of the 

 extremity, often with something, of a contest and knocking of heads 

 together ; but the other will presently be found on one edge, excavating 

 on either side of a narrow strip which is to constitute the base of the 

 perch. This is bound and lengthened with frass and serves every purpose. 



Both these species of larvae have a habit of accumulating little scraps 

 of leaf at the base and under side of the perch till quite a packet is 

 formed, and this is rolled back as the substance of the leaf is eaten so as 

 to be close to the cut edge of the leaf. This edge, in willow, is kept 

 nearly square, a section being eaten from one lobe and then a correspond- 

 ing one from the other. In beginning on a fresh section, the larva lies 

 diagonally across one corner, the anal legs clasping the base of the perch, 

 and its head will strike the side of the leaf about two tenths inch above 

 the corner. It eats a canal nearly perpendicular to the side and towards 

 the midrib ; not all at once, by any means, for this is the result of several 

 meals, in the intervals always returning to the perch. When the rib is 

 reached, the larva then begins to feed on the lower side of the canal next 

 the rib, and to keep the slender and unsteady bit of leaf in position it 

 spins guys from the end and edge to the solid leaf opposite and to the 

 rib. As the feeding proceeds and a considerable triangle is held only by 

 a narrow strip, which diminishes at each mouthful, more guys are put out, 

 and, at last, when the triangle falls, it is held by the threads and swings 

 to the base of the perch. If not, it is soon brought there by fixing one 

 thread after another from it to the rib and leaf till it is pulled to its place. 

 Here it is bound loosely. As other bits are added, there comes to be an 

 open packet, held together by simple threads, and of about one tenth 

 inch diameter. In the two younger stages this is moved along as the 

 larva feeds, and is always kept close to the leaf, partly by pushing, what 

 is gained at each effort being secured by threads, or it is rolled by attach- 

 ing successive threads from the farther side to the leaf and rib till the 

 mass is turned over. After the second stage the packet is left behind, and 

 no additions are made to it. I was at first puzzled to account for this 

 construction ; but happening to see one of the caterpillars back down the 

 perch and drop its excrement directly into the packet, it occurred to me 

 that really this was the magazine whence the larva drew its materials for 

 lengthening the perch. On pulling some of the packets apart a few grains 

 were always found in them. This I believe to be the use of the packets, 

 and without some contrivance to catch the frass. it is difficult to see how 



