680 
ANNUAL REPORT OF NEW YORK 
VAPORER MOTH. THE PARASITE’S OPERATIONS. 
middle, narrowing towards tho base and very slightly towards the tip. Second joint twice as 
long as thick, obconio, and a third narrower than the basal joint. Third joint similar in length 
and thickness to the second, cylindrical. Fourth and fifth joints globular and of the same thick¬ 
ness with the preceding two. Sixth joint a third thicker, globular. Seventh and eighth joints 
thickest of all, their outline square, opposite sides straight and parallel, base and apex slightly 
convex. Ninth joint of the same form but a little smaller. Tenth or last joint narrower and a 
very little longer than the ninth, egg-shaped. Thorax broad egg-shaped with a deeply impressed 
transverse line across its disk back of the center. Abdomen sessile, smooth and highly polished, 
similar to the thorax in its size and form. Wings horizontally incumbent upon the back when at 
rest, smoky hyaline, the fore pair with a straight stiginal branch arising near the middle of the 
outer margin and running obliquely inward and backward, ending abruptly without being 
enlarged into a knob or head, its length about equal to one-third of the width of the wing. 
Legs much more slender than the antennae and rather long, the forward pair shortest, with their 
shanks thick, elliptic-obovate, and having a strong curved spur on the underside towards tho 
tip. Shanks of tho other legs long and slender, and gradually thicker towards their tips, tho 
hind ones longest. Feet long and thread-like, longer than the shanks on which they are respec¬ 
tively inserted, their basal joint longest and occupying a third of the total length, the second and 
fifth joints about equal in length and perceptibly longor than the third and fourth. 
Tin's parasite passes around and punctures the shell of each egg of the 
Vaporer Moth, inserting a minute egg of its own inside, from which hatches 
a maggot which feeds upon and consumes the contents of the moth’s egg. 
Each one of the latter eggs is supposed to contain the exact amount of 
nourishment required for the growth of one of the parasites. Hence the 
parent fly is cautious to never puncture an egg which is already occupied, 
being aware that its young will perish from starvation should two of them 
happen to be placed in the same egg. In the instance which came under 
my observation, seven of these minute flies were engaged upon one cluster 
of eggs, walking slowly about and around them, and examining them with 
their antennas; and with a magnifying glass I could distinctly see one and 
another of them with its sting inserted into an egg, thus leaving no doubt 
as to the nature of the work in which they were engaged. I managed to 
capture two of these flies, and being called away from home, on my return 
three days afterwards the remaining five were still present, busily engaged 
in their operations. On the following day, however, only two of them were 
remaining. That such a number of these flies should continue day after 
day upon the same cluster of eggs shows how pertinaciously they follow 
up this work, never abandoning it until they become fully assured that the 
last egg in the cluster has been ferreted out and inoculated. Although 
there were two other clusters of eggs at distances of only six and ten feet, 
not one of these flies discovered them—which indicates that there was some 
peculiarity about that particular cocoon, whereby such a number of these 
flies were able to find it and failed to detect the other two in its vicinity. 
As the Common Vaporer Moth, 0. leucostigma, covers her eggs copiously 
with a white frothy substance which dries and hardens upon them, com¬ 
pletely enveloping and hiding them from the view, this parasite is unable 
to come at them to destroy them; and this is no doubt one of the causes if 
not the sole cause why that species is so much more numerous than the 
present one in our country. 
It is rarely that the caterpillars of this-moth will occur in such numbers 
on our trees and shrubbery as to excite any solicitude. Should they do so 
