2 BULLETIN 295, U. S. DEPARTMENT OF AGRICULTURE. 
the development of forest trees, with a view of discovering possible 
methods of elimination or at least amelioration of its ravages. 
Definite details were gathered only in certain areas within the 
States of Montana and Idaho, but correspondence with the other forest 
insect field stations in the West, together with larvae collected and 
forwarded from those stations, proves that this moth occurs almost 
everywhere in the West. Considering that Packard records its 
occurrences in New York and Pennsylvania, it is evident that this 
insect is probably distributed over most of the United States. Its 
habits and the result of its larval work also apparently do not vary 
materially anywhere in its range. These facts lead to the conclusion 
that the remedy outlined below should be as effective in other regions 
as in the West. 
DESCRIPTION OF THE INSECT. 
THE ADULT. 
The length of the moth (PI. II, fig. 1) is about one-half inch. There 
is no appreciable difference in size and coloration between the two 
sexes although the general color of individual specimens varies from 
a light gray to a reddish gray and the body of specimens having 
the latter hue on head and thorax is usually dark gray. The under- 
side of the entire insect is of a uniform gray color. 
The wing expanse is from 1 J- to 1 ^ inches. The fore wings are shaded 
reddish on the basal and terminal fields, the median space, divided 
from the latter by W-shaped lines, being blackish and gray, these two 
colors being again divided by a small white bar on a brownish field. 
The hind wings are pale yellowish white, the color becoming deeper 
toward the terminal fringe, which is paler than that of the fore wings, 
on which it frequently shades to a dark gray. These characters 
agree fairly well with Grote's description. 
THE LARVA. 
When full grown the caterpillar (PI. II, fig. 2) is about three-fourths 
of an inch in length. The head is chestnut brown, the mandibles black. 
The body is naked, with a series of dots, darker than the skin, from 
each of which issues a single bristle. It has three pairs of thoracic 
legs, four pairs of abdominal prolegs, and a pair of anal claspers. 
The body varies greatly in color, which ranges from a dirty white, 
through reddish yellow, to a vivid green. The larva found in yellow 
pine is almost invariably gray-brown, resembling the color of the 
bark of the host tree, while those in Douglas fir are of such a vivid 
green color that it seems almost incredible that they should be repre- 
sentatives of the same species which infests pine. Rearing them to 
the adult stage, however, always dispels any doubt in this regard. 
' Variations in color, about which Grote and Kellicott differ, are 
evidently merely a matter of host differences. 
