18 



portions of the body of the full-grown caterpillar are illustrated, 

 greatly enlarged, in fig. 6, and it is the shorter hairs from the sides 

 which probably cause the irritation. They are very small, fall out 

 readily, and, when a caterpillar crawls over the skin of an individual 

 who is warm and perspiring, these very sharply barbed hairs produce 

 an irritation which in some individuals has been the cause of much 

 discomfort, creating more or less inflammation and swelling. 



The larva transforms to pupa within a few hours after the completion 

 of the cocoon, and remains in the pupal condition from ten days to two 

 weeks. The cocoons of this first generation, while mainly spun on the 

 trunk and larger branches, are also spun to a very considerable extent 

 upon the smaller branches and twigs, and even on the partly eaten 

 leaves. 



The adult insect presents the rather unusual phenomenon of a 

 winged, active male and a degraded, absolutely wingless female. It 

 is this fact which makes the spread of the species dependent upon the 

 traveling powers of the caterpillar, as mentioned in the preceding para- 

 graph. The male and female pupae and the male and female moths 

 are so well shown in fig. 4 as to need no description. 



Coupling takes place upon issuing from the cocoon, and immediately 

 afterwards the females begin to lay their eggs, clinging firmly to the 

 cocoons from which they have issued and attaching the egg mass to 

 the lower half of the cocoon, in the manner shown in fig. 4, h and k. 

 As soon as the eggs are laid the females die, and usually fall to the 

 ground, although sometimes their shriveled bodies remain clinging by 

 the legs to the upper part of the cocoon. 



We have made no observations as to the duration of these midsum- 

 mer eggs. Unfortunately, upon the length of time which elapses before 

 hatching depends exact information as to the number of annual gen- 

 erations. Specific observations in 1895 in Washington were not begun 

 until August 15. At that time the egg masses were everywhere to be 

 seen, and about that time the eggs began to hatch. From the early 

 statements of Riley it was assumed that these were the eggs of the 

 second generation, but reference to the notebooks of the office shows 

 that on several occasions overwintered eggs have hatched in Wash- 

 ington in April, and adults have issued as early as the middle of June. 

 From the middle of June to the middle of August is certainly long 

 enough to allow for a generation of this insect. Assuming that such a 

 generation had developed, larvae from these August eggs would belong 

 to the third generation.' This, however, is to a certain extent guess- 

 work, and the regrettable lapse of observations during the last half of 



' Observations made during 1896 confirmed fully the surmise here recorded that 

 the white-marked tussock moth has at Washington three generations annually, 

 instead of two, as previously stated by Eiley. (See Bulletin 10, Division of Ento- 

 mology, p. 33.) 



