State Museum of Natural History. 51 



the pest, but of no utility whatever if the insect be already upon it, 

 either as young larvae or as egg-clusters attached to the branches. It 

 is this insect also, which deposits its eggs upon its cocoon, to the num- 

 ber of two or three hundred, and covers them with a mass of viscid, 

 white, frothy matter, which, hardening by exposure, subsequently 

 remains for months or until discolored by age, as conspicuous objects 

 when placed, as they often are, upon the trunks of elms and larger 

 trees, readily arresting the eye of the passer-by. 



This past summer, contemporaneously with the first appearance of 

 the attack of the caterpillar upon the foliage, the sidewalks, streets 

 and parks where the elm was growing, were seen to be strewed with its 

 green leaves — in many places so thickly as completely to cover the 

 walks or ground. Upon taking them up for examination, they were 

 found to be the tips of the branches, comprising most of the new 

 growth of the season. The portions thus thrown down were about three 

 inches in length and contained from four to ten fresh, uninjured leaves. 

 It was evident that they had not been broken off by an unusually high 

 wind, for each day continued to add to the number and to increase the 

 abundance of the fall. Making critical observation for the discovery, 

 if possible, of so unusual a phenomenon, it was noticed that from 

 above the point at which the twig had been broken, the bark was en- 

 tirely removed for an extent averaging one-tenth of an inch. The 

 manner of its removal showed it to have been eaten by an insect. From 

 its character, together with the abundant presence of the caterpillar 

 upon the trees at the time, I believed that it was the work of the 

 Orgyia. If so, it was of especial interest, as this form of depredation, 

 had never, to my knowledge, been previously observed. To verify the 

 belief, I ascended to a house-top where the branches of a large elm 

 projecting over the roof gave an excellent opportunity for examination. 

 The larvae were abundant upon the tree; the flat roof was strewn and 

 heaped in corners with the broken-off tips ; large numbers of the 

 girdled twigs still held their place on the tree; and by careful search, 

 larvae were discovered in the act of eating the bark. From what was 

 subsequently learned, the girdling had at this time nearly ceased. 



From the above observations, the following explanation of the cause 

 of the girdled and broken-off twigs of the elm may, I think, safely 

 be given. Upon the eating away of the bark by the Orgyia caterpillar, 

 the wood on exposure rapidly dried and soon became so brittle that 

 from a moderate swaying of the branches the weight of a half dozen 

 or more of large and succulent leaves would occasion the breaking of 

 the slender twig — often not exceeding in its dried state the diameter 

 of an ordinary pin. 



For the occurrence at this time of this novel form of the Orgyia 

 attack, I can offer but the following as a plausible explanation. The 

 spring had been remarkably cold, and, as a consequence, the foliage 

 of the trees had been delayed in development quite beyond the ordi- 

 nary time. The sudden advent of warm weather caused a correspond- 

 ing sudden start in vegetation followed by a vigorous growth, and the 

 young twigs of the elm would, as the result, be unusually tender. The 

 particular feeding-ground of many of the lepidopterous larvas is 

 known to be decided upon only after repeated tastings and rejections of 



