748 



REPORT UNITED STATES GEOLOGICAL SURVEY. 



nearly 1,000 species (!), swarm even in our houses, especially in the coun- 

 try, where in October and November I have seen immense numbers in- 

 side of the windows, and 1 believe that they hibernate behind the shut- 

 ters, in the curtains," etc. 



Were it not for the native ichneumon parasite, (Fig. IG, a, male ; fe, 



female,) which has been found to prey upon 

 it very extensively, the cultivation of the 

 cabbage would have to be given up in some 

 tiistricts. This invaluable ichneumon is one 

 of the chalcid family, and is the Pterom- 

 ah(S puparum oH Linnaeus. It is well known 

 that the cabbage-caterpillar (Pie*-;,* rapw) 

 was introduced into this country about the 

 year 1857. I had supposed that the par- 

 asite had perhaps been imported with its 

 host, but now find that it is undoubtedly a 

 native of this country as well as Europe. 

 Having been favored by Mr. Francis Walker 

 with s|3ecimens of both sexes from England, 

 labeled by him Pt. 2nq)arum, I found that 

 our specimens did not differ specificially. 

 Further, Mr. Walker wrote me that there 

 Fig. 16.— Parasite of the im- were specimens of the same species in 

 ported Cabba.^e Butterfly. the British Museum, taken in Hudson's 

 Bay territory in 1844. During the past summer Mr. P. S. Sprague, 

 sent me specimens which had been raised from the rape caterpillar in 

 Vermont. Mr. J. A. Lintner has also published a note in the Ameri- 

 can Naturalist stating that he had reared this parasite from the same 

 kind of caterpillar, and previously to this Mr. S. H. Scudder had re- 

 ceived numerous specimens from Mr. A. G. T. Eitchie, of Montreal, 

 Canada, who, if I understand his letter aright, first observed these 

 cbalcids upon the cabbage-leaves in July, 1870, when the caterpillars 

 were abundant. On the 23d of August of the same year he had some 

 of the parasites hatch out. To Mr. Ritchie, then, is due the credit of 

 being the first to make known the history of this invaluable insect. 



It seems that the parasite covers even a wider field than its host, and 

 probably preys on our native cabbage-butterfly, the Pieris oleracea, as 

 in Europe it preys on Pieris hrassiccc, the caterpillar so destructive to 

 the cabbage there. 



Description. — The male of this Pteromalus is a beautiful pale-green fly, with the 

 body finely punctured and emitting metallic tints; the abdomen, or liiud body, is flat, 

 in dried specimens with a deep crease along the middle of the upper side, and it is 

 much lighter in color and with more decided metallic reflections than in the rest of 

 the body. The antenna} are honey-yellow, with narrow black wings. The legs are 

 pale honey-yellow. It is .08 inch to a tenth in length. 



The liody of the female, which would bo thought at first to bo an entirely difi'erent 

 kind of insect, ismuch stouter, broader, with a broader oval abdomen, ending in a very 

 short ovipositor, while the under side of tlio body near the base has a large conical 

 projection. It is ranch duller green than the male, and the body is more coarsely 

 punctured. The scutellura of the metathorax is regularly convex, not keeled, in both 

 sexes. The antenna? are brown, and the legs l)ro\vn, becoming pale toward the ends, 

 the ends of the femora being pale ; the tibire pale brown in the middle, much paler at 

 each end, while the tarsi are whitish, though the tip of the last joint is dark. It is 

 from a line to a line and a third in length. It diftors from Harris's I'teromalus vanenscB 

 in the little piece known as the scutellum of the metathorax being smooth, not keeled, 

 and by its darker legs. 



The larva is a little white maggot about a sixth (.17) of an inch in length. The 

 body consists of thirteen segments, exclusive of the head, and is cylindrical, taper- 

 ing rapidly toward the head, while the end of the body is acutely pointed. The 

 chrysalis is whitish, the limbs being folded along the under side of the body, the 



