io8 INJURIOUS AND USEFUL INSECTS 



As soon as Reaumur's parasitic larvae became free, they began 

 to spin themselves cocoons of silk, very similar to small-scale 

 copies of a silkworm's cocoon, and of the same golden colour. 

 Within these cocoons the insects remained long unchanged. 

 Thus larvae which span up in December were still larvas on 

 April 23rd. Very soon afterwards they turned to white pupje, 

 and the flies emerged before the end of the month. Hymen- 

 optera often prolong the resting stage at the expense of the 

 pupa-stage (see saw-fly, p. 97), whereas in Lepidoptera the 

 resting larva quickly changes to a pupa. 



Such is the history of the ichneumon of the cabbage white, 

 as condensed from Reaumur. The fly is technically named 

 Microgaster (or Apanteles) glomeratus ; it is 3 mm. long. 

 The abdomen is short, of few segments, and sessile, or appar- 

 ently so. The pattern of the wing is materially different from 

 that of a Pimpla or an Ophion. Many ichneumons resemble 

 Microgaster in the venation of the wing, and are grouped as 

 the family Braconidse. The Braconidse are usually, but not 

 quite always, social, many being reared within one host. 

 Microgaster pupae are often found sticking in clusters to 

 palings or similar objects close to a cabbage-plot. They are 

 preyed upon (one might call it a just retribution !) by secondary 

 parasites, minute Hymenoptera of the family Chalcididae. 



Among the Braconidse is an ichneumon which attacks 

 aphids. This is Aphidius rosarum, which is often to be met 

 with on rose-bushes. The fly is yellow and black, 2 mm. long, 

 with stalked abdomen, and short, few-jointed feelers. The 

 female Aphidius sends its borer forwards between its legs till 

 it projects beyond the head. In this singular attitude it pierces 

 a wingless aphid, which soon ceases to move, turns yellow, 

 and becomes unnaturally inflated. The parasitic larva devours 

 all the contents of the body, forms no cocoon, but pupates 

 within the inflated abdomen in a doubled-up posture. The fly 

 bites a circular lid out of the abdomen of the dried aphis, and 

 emerges through the hole. 



There is also a numerous family of egg-boring ichneumons, 

 which draw their whole substance from single eggs of spiders 

 or insects. One egg has been known to maintain several para- 

 sites. The minute egg of the Hessian fly provides both space 

 and food for a parasite called Platygaster, which is remark- 

 able for its complicated transformations. In certain stages it 



