PARASITE INSECTS, 61 



It must have occurred to the least attentive obser- 

 vers of the very common cabbage caterpillar {Pontia 

 Brassiccf), that when it ceases to feed, and leaves its 

 native cabbage to creep up walls and paHngs, it is 

 often transformed into a group of little balls of silk, 

 of a fine texture and a beautiful canary yellow colour; 

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

 small four-winged fly (yMicrogasUr giomercdiis, Spi- 

 ivola), 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 

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

 dily take alarm; but, as Reaumur justly remarks, will 

 permit an observer to approach her with a magnifying 

 glass of a very short focus. Having deposited one 

 egg, she withdraws her ovipositor, and again plunges 

 it with another egg into a difl^erent part of the body of 

 the caterpillar, till she has laid in all about thirty eggs. 

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

 whose body is thus pierced with so many wounds, seems 

 to bear it very patiently, 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- 



VOL. VI, 6 



