252 TRANSACTIONS OF THE ILLINOIS 



another places its eggs on the outside of the chrysalis, so that when hatched 

 the little grubs can work their way into the interior. The last of these, 

 the Pteromalus puparutn of Linnseus, is found also to be a native of this 

 country; and since the advent of the European cabbage-butterfly, which 

 we are now describing (^Pieris rapce) has manifested its disposition by 

 attacking the chrysalis. It was not known that this chalcid was a native 

 of this country, but when observed was supposed to be an importation 

 which had been brought over from the Eastern continent with its host, 

 until Dr. Packard, by comparison of specimens found here and in England, 

 ascertained they belong to the same species. 



This little Hymenopterous insect, rather less than one-tenth of an 

 inch long, is wasp-like in form, with four delicate, transparent wings, very 

 slightly reflecting the prismatic colors, the anterior pair with a single short, 

 dull-yellowish nerve ; the head very short and broad ; the body of the 

 female is a blackish-green, that of the male somewhat pale-green. 



The following more exact description is by Dr. Packard : 



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

 body finely punctured and emitting metallic tints; the abdomen or hind body is fiat 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 refiections than the rest of the 

 body. The antennge are honey-yellow, with narrow black wings. The legs are pale 

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



The body of the female, which would be thought at first to be an entirely diff'erent 

 kind of an insect, is much stouter, broader, with a broad, oval abdomen, ending in a 

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

 projection. It is much duller green than the male, and the body is more closely 

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

 sexes. The antennae are brown, and the legs brown, becoming pale towards the ends, 

 the ends of the femora being pale ; tibiae 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. The larva is a little white maggot about a sixth (.17) 

 of an inch in length. The bod^ consists of thirteen segments, exclusive of the head, 

 and is cylindrical, tapering rapidly towards the head, vs^hile the end of the body is 

 acutely pointed. The chrysalis is whitish, the limbs being folded along the under side 

 of the body, the antennge reaching to the end of the wings ; the second pair of legs 

 reaching half way between the end of the wings and the end of the abdomen ; while 

 the tips of the third pair of feet reach half way between the second pair of feet and the 

 end of the abdomen. It is from a line to a line and a third in length. 



The female deposits her eggs upon the outside of the chrysalis of 

 the butterfly as soon as the caterpillar has cast off its skin, when it is soft, 

 tender and exhausted by the severe change which it has undergone. 

 These eggs soon hatch, and the little grubs at once eat their way into the 

 body of the chrysalis, the interior of which at this time is in an almost 

 liquid state. The number of these maggots which live in one chrysalis 

 is often very great, sometimes amounting, according to Curtis, to as 

 many as two or three hundreds, but according to my observations, which 

 appear to agree with those of Dr. Packard, the more usual number is from 

 ten to thirty. They appear to consume the entire interior, filling it up 

 with their bodies and entire exuviae. 



In the pupa shells which I have opened, some of which are now 

 before me, I find that all the parasites have not escaped, but in each there 



