PARASITE INSECTS. 61 



It must have occurred to the least attentive obser- 

 vers of" the very common cabbage caterpillar {Pontia 

 Brassiccv), that when it ceases to lecd, and leaves its 

 native cabbage to creep up walls and palings, it is 

 often transtbrnicd into a group of little balls of silk, 

 of a line texture and a beautiful canary yellow colour; 

 from each of which there issues, in process of time, a 

 small four-winged fly {JMicrof^uster glouui'alris, SiM- 

 nola), of a black colour, except the legs, which are 

 yellow. By breeding these flies in a state of confine- 

 ment, and introducing them to some cabbage caterpil- 

 lars, their proceedings in depositing their eggs may be 

 observed. We have more than once seen one of these 

 little flies select a caterpillar, and perch upon its back, 

 holding her ovipositor ready brandished to plunge be- 

 tween the rings which she seems to prefer. When 

 slie has thus begun laying her eggs, she does not rea- 

 dily take alarm; but, as Ri'aumur justly remarks, will 

 permit an observer to ap|)ioach her with a magnifying 

 glass of a very short focus. Having deposited one 

 egg, she withdraws her ovi[)ositor, and again plunges 

 it with another egg into a different part of the body of 

 the caterpillar, till she has laid in all about thirty eo;gs. 

 It is not a little remarkable, that the poor caterpillar, 

 wiiose body is thus pierced with so many wounds, seems 

 to bear it very |)aticntly, and does not turn upon the 

 fly, as he would be certain to do upon another cater- 

 pillar should it venture to pinch him; a circumstance 

 by no means unusual. Sometimes, indeed, he gives 

 a slight jerk, but the fly does not appear to be at all 

 incommoded by the intimation that her presence is dis- 

 agreeable. 



The eggs, it may be remarked, are thrust suffi- 

 ciently deep to prevent their being thrown off when 

 the caterpillar casts its skin; and, being in due time 

 hatched, the grubs feed in concert on the living 

 body of the caterpillar. The most wonderful circum- 



vor,. VI. 6 



