THE AMERICAN ENTOMOLOGIST. 



101 



according to Mi-. Trouvelot, deposits from eight 

 to ten eg-gs upon the skin of her victim, and the 

 young larvae soon hatch from them and com- 

 mence to prey upon the fatty parts of tlie woim. 

 But as only one of the parasitic larvae can find 

 food sufllcient to mature, the rest all die from 

 hunger, or else are devoured by the strongest 

 one which survives them. At first one would 

 suppose that this deposition of several eggs by 

 the parent Ichneumon, where only a single 

 larva can develop, is a striking instance of mis- 

 directed instinct; but we find a similar prodi- 

 gality throughout Nature, for every individual 

 is so subject to disasters of one kind or another 

 in its struggle for existence, that a provision of 

 several ova is often necessary to insure the 

 future development of a single one, just as we 

 often sow several seeds of some particular plant, 

 in order to insure the growth of a single one. 



After the Cecropia worm has formed its co- 

 coon, the parasitic larva, which had hitherto 

 fed on the fatty portions of its victim, now 

 attacks the vital parts, and when nothing but 

 the empty skin of the worm is left, spins its 

 own cocoon, which is oblong-oval, dark brown 

 inclining to bronze, and spun so closely and 

 compactly, that tiie inner layers when separated 

 have the appearance of gold-beater's skin. If 

 we cut open one of these cocoons soon after it 

 is completed, we shall find inside a large fat 

 legless grub (Fig. 64), which sometimes iinder- 



[Fifc- M.] 



Color— Yellowish. 



goes its transformations and issues as a fly in 

 the fall, but more generally waits till the fol- 

 lowing spring. 



The Cecropia Taciiina Fly.— The Ichneu- 

 mon fly last mentioned usually causes a dwarfed 

 appearance of the worm which it infests, and 

 parasitized cocoons can generally be distin- 

 guished from healthy ones by their smaller 

 size. The larvse of the Tachina fly, which we 

 now introduce to our readers, as parasitic on 

 the (Cecropia worm, seem to produce an exactly 

 opposite effect — namely, an undue and unna- 

 tural growth of their victim. In the beginning 

 of September, 1866, we received from Rocktord, 

 Ills., an enormous Cecropia worm. It measured 

 over four inches, was a full inch in diameter, 

 and weighed nearly two ounces; but like many 

 other large specimens which we have since seen, 



it was covered with small oval opaque white 

 egg-shells, clusters of four or five occun-iiig on 

 the back of each segment, invariably deposited 

 in a transverse direction. The skin of the 

 worm was black where the young para'-ites 

 had hatched and penetrated. This large worm 

 soon died and rotted, and in about twelve days 

 a host of maggots gnawed their way through 

 the putrid skin. These maggots averaged about 

 one-half inch in length, and iu form were like 

 those of the common Blow-fly. The head was 

 attenuated and retractile and furnished with 

 two minute curved hooks, and the last segment 

 was squarely cut oflT, slightly concave and willi 

 the usual two spiracles or breathing-holes which 

 this class of larvae have at their tails. Their 

 color was of a translucent yellow, and they 

 looked very much like little pieces of raw fat 

 beef. They went into the ground and remained 

 in the larva s'tateall winter, contracted to pupa' 

 in the April following, and the flies commenced 



[Fig. 65.] 



to issue the last of 

 May. This fly is 

 the Exorista ce- 

 cropia ofourMS., 

 or Cecropia Tach- 

 ina Fly, but as it 

 diflers from the 

 Red-tailed Tach- 

 ina Fly {Exorista 

 mill tar is, Walsh, 

 Fig. 6o), which 

 Colors-GiHy and black. similarly infests 



the Army-worm, in no other respect than 

 in either lacking the red tail entirely, or in 

 having only the faintest trace of it; and as 

 in a lot of the militaris bred last summer 

 from Army-worms, we find considerable dif- 

 ference in this respect, we prefer, rather than 

 multiply species ou such mutable grounds, to 

 consider it as a variety of that species. We 

 infer that this same Tachina fly attacks the 

 Cecropia worm in widely difterent parts of the 

 country ; for we have this winter received from 

 Mrs. Mary Treat, of New Jersey, two dipterous 

 pupae which probably belong to this species, 

 and which had also in the larva stale infested 

 a Cecropia worm. 



The Cecropia Chai.cis Ply — (Chalcis maria. 

 N. Sp.*) — In May, 1869, we received from Mr. 



'Chalcis 



S s;p.-$ yellow, beautifully 



ilikeil 



■dge Ijl.ick, llagfllum dark brown (.r black. Thurax with 

 arge shallow close-set jjunctures; mesothorax somewhat 

 striated transversely, trilineur with black, the three lines 



