256 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION 
attention will soon reveal large numbers of thetn. Upon the trunks of various 
trees, bu1 ohiefly upon those of the poplars and sugar maples, sinaH colonies of cater- 
pillars, varying in numbers from four to twelve, eouid be observed, which did not 
show any sign of life. Wben removed from the tree they appeared contracted, all 
of the same Sise, and pale or almost white. A closer inspection would reveal the 
fact that the posterior portion of the caterpillar bad ehnmkao away to almost noth- 
ing, whilst the real ffH somewhat inllated and covered with an unchauged bur 
bleached skin, retaining all the hairs in their normal position. Opening one ot 
these inflated skins, a long cylindrical, brown cocoon would be exposed; this is the 
cocoon of the Linuieria under consideration. As numbers of such inflated skins 
would always occur together, it was clearly seen that the same parent Limneria had 
oviposited in all of them. Most of the cocoons were found in depressions of the rough 
bark or other protected places. Single ones were but rarely met with. The 
Hyphantria larva in dying had very securely fastened all its legs iuto the crevices of 
the bark, so that neither wind nor rain could easily dislodge them. Only half-grown 
caterpillars had thus been killed. Many of these inllated skins showed in the early 
pail of October a large hole of 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 cocoons — and only such as were not perforated in any 
way — were collected and put iu a glass jar. Only a single female was produced 
from all up to the 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 spriug of 1887, because some of these inflated skins show as yet no holes 
of exit. 
Tachina sp. (Fig. 95.) — The parasites of H. cunea described so far all belong to the 
order Hynienoptera, which furnishes the greatest number of them. But the fly now 
to be described is fully as useful as any of the others. 
Tachina-llies are very easily overlooked, because they resemble large house-flies 
both in appearauce and in flight, and their presence out of doors is not usually 
noticed on that account. Yet they play a very im- 
portant 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 yellowish-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 can not easily be removed. 
Fig. 95.— A~Tachina-flv. 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 cater- 
pillar where they soon reach their full growth, after which they force their way 
Through the skiu and drop to the ground, into which they enter to shrink into a 
brown, tun-like object (known technically as the coarctate pupa), which contains 
the true pupa. The caterpillar, tormented by enemies feeding within it, stops feed- 
ing and wanders about for a long time until it dies. As a rule, not more thau two 
maggotfl 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-tlies 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, 
