52 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 
in theearly part of October a large hole ot exit in their posterior and 
dorsal ends, from which the ichneumons had escaped. Trying to obtain 
winged specimens of this parasite one hundred and forty of these co- 
coous—and only such as were not perforated in any way—were collected 
and put in a glass jar. Only a single female was produced from all up 
to time of writing, whilst very large numbers of secondary parasites 
issued from October 11 till the 20th of November, and doubtless others 
will appear during the spring of 1887, because some of these inflated 
skins show as yet no holes of exit. 
‘‘ Tachina sp. (Fig. 26.)—The parasites of H. 
cunea described so far all belong to the order 
Hymenoptera, which furnishes the greatest 
number of them. But the fly now to be de- 
scribed is fully as useful as any of the others. 
‘¢Tachina-flies are very easily overlooked, 
because they resemble large house-flies, both 
inappearance and in flight, and their presence 
out of doors is not usually noticed on that 
account. Yet they play a very important 
role, living as they do in their larval state 
entirely in insects. During the caterpillar plague such flies were often 
seen to dart repeatedly at an intended victim, buzz about it, and quickly 
disappear. If the caterpillar thus attacked was investigated, from 
one to four yvellowish-white, ovoid, polished, and tough eggs would be 
found, usually fastened upon its neck, or some spot where they could 
not readily be reached. These eggs are glued so tightly to the skin of 
the caterpillar that they cannot easily be removed. Sometimes as many 
as seven eggs could be counted upon a single caterpillar, showing a 
faulty instinct of the fly or flies, because the victim is not large enough 
to furnish food for so many voracious maggots. If the victim happens 
to be near a molt, it casts its skin with the eggs and escapes a slow but 
sure death. But usually the eggs hatch so soon that the small maggots 
have time to enter the body of the caterpillar, where they soon reach 
their full growth, after which they force their way through the skin 
and drop to the ground, into which they enter to shrink into a brown, 
tun-like object (known technically as the coarctate pupa), which con- 
tains the true pupa. The caterpillar, tormented by enemies feeding 
within it, stops feeding and wanders about for along time until it dies. 
Asarule not more than two maggots of this fly mature in their host, and 
generally but one. The caterpillar attacked by a Tachina-fly is always 
either fully grown or nearly so. 
“Tachina-flies abounded during the whole term of the prevalence of 
the caterpillars. But it is impossible to state positively whether they 
were all bred from them or not, since the many species of this genus of 
flies resemble each other so closely that a very scrutinizing investiga- 
tion would have been necessary to settle such a question. But there is 
no doubt that they were very numerous during the summer. Some 
Fic. 26.—A Tachina-fly. 
