246 THE ENTOMOLOGIST. 



prelude to a journey into the interior of the cabbage. Immediately 

 the caterpillar felt the prick of the ovipositor the fly was flung off, 

 but in one instance, probably through the weariness of the larva, 

 the fly was in position three seconds before it was thrown off. But 

 it was not clear what was the nature of the defence which the larvae 

 had against the fly. 



After about three-quarters of an hour the caterpillars grew 

 hungry and three or four of them climbed up to the edge of the leaf 

 and began to feed ravenously. Presently a Microgaster appeared 

 on the opposite side of the leaf and slowly approached. I watched 

 through my glass and saw the mode of attack and the nature of the 

 larva's defence. The caterpillar, conscious of danger, ceased feeding, 

 and the fly crept up until she had reached a position with one leg 

 on each side of the caterpillar's head and gently waved her antennas. 

 With a sudden spring she was on its back and instantly the heads 

 of the four larvae were turned towards the fly, while their move- 

 ments were so rapid that I could not follow them. It was like 

 watching a cat set on by four dogs. In about three seconds the 

 fly was thrown off and was dragging its body and struggling along 

 the leaf. I examined it through the glass and found it was com- 

 pletely drenched in green liquid, which fastened the wings to the 

 body and stuck the legs together so that they were useless and 

 dragged behind. The liquid was so abundant that wherever the 

 fly went she left a trail of it behind her. Now she began the same 

 industrious toilet which I had seen the others perform, and when 

 cleansed seemed glad to escape and fly away. 



If the Microgaster lays her eggs only inside the eggs of Pieris 

 brassicae what were these flies doing, and why this careful stalking 

 and fierce persistent attacks in spite of the unsavoury green liquid 

 with which they were drenched ? The fear of the larvae as shown 

 by the jerking of their heads in unison and their refraining from 

 food proves that it is a recognised danger, the knowledge of which 

 must have come down to them through many generations. 



We had a plague of Pieris in West Cornwall which stripped the 

 cabbage and turnip fields, and so numerous were the larvae that it 

 was impossible to put the foot down without crushing them . Nature 

 provided the only effective remedy and the Microgaster cocoons 

 were everywhere. They could be found on nearly every flowering 

 stem of thrift and plants of like character, and at Gwinnear Koad 

 Station, where there is a wall about three hundred yards long, the 

 wall was covered with them. Selecting a space covering one 

 square yard of the wall I counted 100 cocoons, each of which con- 

 tained from fifty to two hundred chrysalids. The entire space of 

 the wall was covered in like manner. 

 Port hie ven, 



Helston, 

 Cornwall. 



