A NEW I'ORM OF ORGYIA ATTACK. 87 



growth of the season. The pieces were from two to three inches in length, 

 each bearing from four to ten fresh uninjured leaves. It was evident 

 that they were not being broken off by unusually high winds, for even 

 in the absence of winds, each day continued to add to their number and 

 to increase the abundance of the fall. 



Making critical observation for the discovery, if possible, of the cause 

 of so unusual a phenomenon, it was noticed that from above the point 

 at which the tip had been broken, the bark was entirely removed for an 

 extent averaging one-tenth of an inch, presenting the appearance shown 

 in Fig. II. The manner of its removal showed it to have been eaten by 

 an insect. The suggestion was made to me that it was the work of some 

 small insect of similar habits to those of the twig-girdler, Oncidcres 

 cimjulatiis (Say), but the closest examination failed to show either scar 

 or egg within the tip. 



From the character of the injury, together with the abundant pres- 

 ence of the caterpillar upon the trees at the time, and of no other ob- 

 served depredator, I believed that it was the work of the Orgyia. If 

 so, it was of especial interest, as showing a new habit developed, for 

 this form of attack had never been recorded of the insect. To verify 

 the belief, after ascending some trees and examining branches within 

 reach from windows, I went upon a house-top, where the limbs of a 

 large elm, projecting over the roof, gave an excellent opportunity for 

 examination. The larvoe were abundant upon the tree ; the flat roof 

 was strewn over and heaped in corners with the broken-off tips ; very 

 many girdled tips still held their place on the tree ; and after careful 

 search, Orgyia larvae were discovered in the act of eating the bark at 

 the girdled points. From later observations, it appeared that the gird- 

 ling had at this time nearly ceased. 



The following explanation of the cause of the falling of the girdled 

 tips seems a rational one. Upon the eating away of fhe bark by the 

 Orgyia caterpillar, the wood rapidly dried from its exposure to the air 

 and arrest of circulation, and soon became so brittle that from a mod- 

 erate swaying of the branches, the weight of a half dozen or more of 

 large succulent leaves would occasion the breaking-off of the slender 

 twig — often not exceeding, in its dried state, the diameter of an ordi- 

 nary pin. 



For the occurrence at this time of this novel form of Orgyia attack, I 

 can only offer the following as a plausible explanation : The spring 

 had been remarkably cold, and as a consequence, the development of 

 the foliage had been delayed to quite beyond the ordinary time. The 

 sudden advent of warm weather caused a corresponding sudden start 

 in vegetation, followed by a vigorous growth, and the young tips of the 



