256 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION 



attention will soon reveal large uiiaibers of them. Upon the trunks of various 

 trees, but chiefly upon those of the poplars and sugar maples, small colonies of cater- 

 pillars, varying in numbers from four to twelve, could be observed, which did not 

 «how any sign of life. When removed from the tree they appeared contracted, all 

 of the same size, and pale or almost white. A closer inspection would reveal the 

 fact that the posterior portion of the caterpillar had shrunken away to almost noth- 

 ing, whilst the rest was somewhat inflated and covered with an unchanged but 

 bleached skin, retaining all the hairs in their normal position. Opening one of 

 these inflated skins, a long cylindrical, brown cocoon would be exposed; this is the 

 cocoon of the Limneria 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 into 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 inflated skins showed in the early 

 part 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 spring 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 Hymenoptera, which furnishes the greatest number of them. But the fly now 

 to be described is fully as useful as any of the others. 



Tachina-flies are very easily overlooked, because they resemble large house-flies 

 both iu appearance 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^achina-fly. 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 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 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 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. 



