124 THE CANADIAN ENTOMOLOGIST 



throughout their further stages. When mature they may be briefly described 

 as follows: 



Length about 14 mm.; body dull white; head shining black; thoracic shield 

 widely margined on sides and narrowly posteriorly with black; thoracic legs 

 dull black; prolegs whitish. Tubercles large, flat, but difficult to define on ac- 

 count of the pale colour. 



In 1918 the trees were still without leaves at the time the larvae commenced 

 to appear though here and there, odd buds had burst sufficiently to enable the 

 young caterpillars to obtain a certain amount of food, a majority, however, 

 being obliged to remain without it for some days longer. The spring of 1918, 

 however, had been an abnormally early one and in consequence, induced an 

 early hatching of the larvae besides causing the leaves to appear before their 

 usual time. Thus the larvae had already commenced to curl the leaves when 

 the weather suddenly changed from extreme heat to severe cold the effect being 

 to kill the latter and in consequence entirely cut off the insects' food supply. 

 The result was naturally disastrous to the caterpillars and caused a great many 

 to die of starvation. It is possible that the mortality may have been due to 

 cold also, but from the fact that large numbers of larvae were observed crawling 

 about in search of food afterwards, the evidence indicates that lack of it was the 

 principal cause of death. The threatened devastation of the poplar leaves in 

 1918 was thus reduced, by the meteorological condition alone, to comparative 

 insignificance though sufficient larvae survived to provide various local out- 

 breaks the following year. 



In 1919, larvae appeared soon after the poplars began to leaf out and by 

 May 12 had curled 50 per cent, of the leaves on certain clumps of trees. The 

 insects developed very quickly. By May 27 many had become fully mature 

 and were dropping from the trees in large numbers. To observe the falling of 

 the caterpillars when they are about to pupate, is a very interesting incident; 

 the larvae apparently prepare themselves for the drop by crawling to the edge 

 of their shelter and fastening themselves firmly to the leaf by means of a silken 

 thread. Here they remain until a breeze sweeps through the trees when the 

 shaking causes them to loosen their hold and they come down in a regular shower, 

 the web affording just enough check to prevent a direct fall. As the insects 

 reach the dead herbage the rattle sounds not unlike that of a sudden shower of 

 rain but so quickly the larvcie wriggle out of sight that unless careful watch is 

 kept they are apt to entirely escape detection. These showers of caterpillars 

 may continue intermittently for several hours there being an absolute lull in 

 activity between the gusts of wind, though there is little doubt that they would 

 let themselves down in any case should the weather remain calm. The larvae 

 at the time they drop, are quite devoid of internal colour matter such as that 

 provided by food, and present a dull white appearance with a brownish head 

 and a small patch of the same colour on the front portion of the sides of the 

 thoracic shield. 



Pupation takes place below the dead leaves usually a short distance m the 

 soil. The pupal stage lasts from early June until the following spring, or ap- 

 proximately 10 months. 



