HENRI FABRE AND THE MICROGASTER. 245 



HENRI FABRE AND THE MICROGASTER. 

 By Rev. G. W. Crutchley. 



Surely Fabre, that " incomparable observer," cannot err in 

 liis notes on the Microgaster, vet I am puzzled to account for 

 what I have seen of its activities. Fabre tells us that these flies do 

 not attack the larvae of Pieris brassicae, but that they deposit their 

 eggs in the eggs of the butterfly. He enclosed Microgaster glomeratus 

 with the larvae of Pieris brassicae without result. But as soon aa 

 he substituted eggs for caterpillars the flies eagerly used their ovi- 

 positors and laid their eggs inside the eggs of the butterfly. The 

 larvae of Pieris brassicae emerged from the eggs, and developed 

 without any apparent inconvenience from the parasites which 

 hatched out within their tissues. When the larva of Pieris was 

 about to pupate the larvae of Microgaster issued from one of the 

 spiracles and formed the familiar yellow silk cocoon, in which they 

 pass the pupa stage of their development. 



Gathering the eggs of Pieris brassicae I kept them until the 

 larvae appeared, then fed them until they had moulted four times. 

 Then I placed them on a cabbage which was growing in a convenient 

 position for observation and visited them every day. One day 1 

 noticed a great deal of agitation amongst the caterpillars. They 

 had left off feeding, and every five or six seconds the upper half of 

 their bodies was jerked violently back. This action was continuous, 

 always with the pause of five or six seconds, then simultaneously 

 all the larvae would throw back their heads as by a common impulse. 

 They were gathered in groups of from six to eight, though there 

 were a few solitary ones. I sat and watched them with the aid of 

 a glass for over an hour and was well rewarded for my pains. 



Presently I saw Microgaster flies coming singly and settling on 

 the cabbage, while I noticed others climbing painfully up from the 

 centre of the plant. As I watched a Microgaster fly alighted near 

 the head of a caterpillar that was quieter than the others. She 

 approached warily and appeared to touch and soothe the larva, 

 with her antennae. Suddenly she sprang on the back of the 

 caterpillar and it immediately swung its head round and apparently 

 bit the fly, though I found out afterwards that in this I was mistaken. 

 The Microgaster was tumbled down into the cabbage and afterwards 

 I saw it climbing back slowly and with difficulty. I watched 

 another fly very busily cleaning its antennae, legs, wings and abdo- 

 men for a long time, and I wondered why. T also noticed a green 

 fluid on the surface of the cabbage leaves. Single flies continued 

 to arrive and others were still struggling out of the centre "l the 

 cabbage. The one which had been so long at its toilel flew away 

 as though glad to be gone. Several others attacked t lie caterpillars. 

 always in the same way and with the same result. It was a certain 



