6 
Washington. Its place in that city seems to have been taken largely 
by the fall webworm (larva of Hyphantria cunea Drury) and the bag- 
worm (larva of Thyridopteryx ephemereformis Haworth). The tussock- 
moth larvie, however, have been moderately common year after year, 
but not until 1895 did they increase so as to attract general atten- 
tion. In 1895, however, Washington suffered from an extraordinary 
outbreak of this insect, as the writer has already pointed out in his 
article on ‘The shade-tree insect problem in the eastern United States,” 
published in the Yearbook of the Department of Agriculture for 1895, 
pages 561-3584. In this season the trees along many streets were com- 
pletely defoliated, and in the autumn they were plastered in the most 
unsightly way with their cocoons. 
In August, 1895, the writer commenced a careful investigation of the 
life history of the insect with the feeling that, although much had 
already been written upon the species, there was still more to be learned 
aboutit. As amatter of fact, new and important points in the life his- 
tory have been determined in the course of this study, but none of 
them are of so much interest as the facts relating to the extraordinary 
phenomena of parasitism, induced by the unprecented multiplication of 
the species. 
Many observations are recoyded which show the prominent part 
which parasites take in the reduction of an insect which under favor- 
able conditions has exceeded its normal bounds in respect to numbers. 
Such constant struggles between species in the apparent effort to pre- 
serve a just balance are met with by every observer in the course of 
nearly every season’s observations. The writer has, however, always 
desired an opportunity to study the exact details of such a struggle 
upon a large scale, and this opportunity was afforded in this instance. 
In Boston, New York, Brooklyn, and Philadelphia the tussock moth 
has not seemed to fluctuate seriously in point of numbers. It has been 
more or less injurious every season for a number of years. In Wash- 
ington, however, in 1895, there was a rapid and enormous increase, and 
great fears of its continuance year after year were expressed by city 
authorities, by the newspapers, and by citizens interested in the beauti- 
ful shade trees of the city. By the time the third generation had made 
its appearance in September, 1895,' it was noticed that parasitic and 
predaceous insects were present in enormous numbers. The cocoons of 
the second generation were the rallying point of hordes of Ichneumon 
and Chaleis flies, while several species of predatory Heteroptera were 
present in great numbers. The trunks of nearly all of the large trees 
in the Government parks were sanguinary battlefields where the result- 
ing mortality was excessive. 
Prior to the beginning of these observations seven species of prob- 
able primary parasites of the tussock moth had been recorded. Fitch 
'Observations of 1896 have shown withoat doubt that there are three annual gen- 
erations in Washington instead of two, as previously stated. (See Bulletin No. 10, 
Division of Entomology, p. 33.) 
