16 
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 prob- 
ably 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 pup 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, larve 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 


the white-marked tussock moth has at Washington three generations annually, 
instead of two, as previously stated by Riley. (See Bulletin 10, Division of Ento- 
mology, p. 33.) 
