THE WHITE-MARKED TUSSOCK-MOTH. 3 I 



-•From tbe character of the injury, together with the abundant 

 presence of the caterpillar upon the trees at the time, ami of no other 

 observed 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 

 leach 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 larva- 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. 



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

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

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

 and a rest 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 — otten not exceeding in its dried state the diameter of an ordinary 

 pin. 



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

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

 had been remarkably cold, aud 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 

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

 the elm would, as the result, be unusually tender. The particular feed 

 ing ground of many of the lepidopterous larvae is known to be selected 

 only after repeated tastings and rejections of such portions of their 

 food-plant as they traverse and a final acceptance of that most agree- 

 able to them. By a process like this tUe Orgyia may have made the 

 discovery that just at the commencement of the new growth, as the 

 result of the seasonal conditions above mentioned, there was concen- 

 trated in the tender bark nutriment far more acceptable to it than that 

 offered in the leaves, upon which alone it had hitherto been accustomed 

 to feed. As the bark hardened with the advancing season it would 

 cease to be desirable for food. * * * 



"On my return to Albany for a few days, on the 21st of July, most of 

 the tips then falling and many of those upon the ground presented a 

 new feature. The breaking, instead of being at the base of the girdling, 

 lust above the commencement of the new growth, was. in these, at the 

 preceding node, covering the growth of the former year. As a rule, 

 the twigs showed a greater diameter at their decorticated portion, com- 

 pared with those of the earlier fall, and the leaves attached to them had 

 been all more or less eaien by the Orgyia. Their greater strength had 

 permitted them to remain longer upon the tree, and until the death of 

 the preceding internode, wjiich soon followed the arrest o( the circula- 

 tion — its starvation ensuing — it being unprovided with leaves through 

 which a circulation could still be maintained. When dead, a slight 

 movement of the branch by the wind, or even tin 1 weight of the terminal 

 leaves, would be sufficient to disconnect it at its lower and weaker node. 

 In a lew instances, where the girdling had been at a little distance 

 above the node marking the commencement of the present year's growth, 

 the separation had been at this point, while others separated iu this 



