514 



NATURAL HISTORY OF ARTHROPODS. 



Fig. 641. — Bracon palpebi^aior. 



sents a caterpillar from which the full-grown larvje of a Microgaster are emerging, and 

 a greatly enlarged figure of an adult Microgaster. The adult insect, in emerging from 



the cocoon, cuts a beautiful little lid at its upper end. 

 Bunches of white or yellow cocoons of Microgaster are 

 often found attached to grass or other objects. These 

 are made by larv£e which on leaving their victim crawl 

 away from it a short distance before transforming. 



Perhaps the most interesting of the common forms 

 belonging to the Braconidse is the genus Aphidius. The 

 members of this genus are minute creatures which infest 

 plant lice. If colonies of plant lice (Aphides) be exam- 

 ined, the dried bodies of dead ones may be found in which 

 the abdomen is more or less spherical, being greatly dis- 

 tended. These bodies remain clinging to the leaves in 

 the position in which the insects were when they d'.ed. 

 From each one there emerges in due time an Aphidius. The parasite, in emerging, 

 cuts a very regular circular lid in 

 the dorsal wall of the abdomen of 

 its host. I have watched with 

 much interest these little Brac- 

 onids ovipositing in the bodies of 

 plant lice. The female alights 

 upon a leaf and runs about among 

 the plant lice. When she has 

 selected one in which to oviposit, 

 she stands with hei- head towards 

 it, and bending her abdomen under 

 her thorax between her legs, she 

 darts her ovipositor forward into 

 the body of the aphis. The Aph- 

 idii do not construct cocoons, but 

 undergo their metamorphoses within the dried skins of the plant lice. 



The IcHNEUMONiDJE proper includes the lar- 

 gest species of ichneumon-flies as well as many 

 minute forms. The characters of this family and 

 generalizations respecting the habits of its mem- 

 bers have been given above in the discussion of 

 the Braconidae. We will now merely indicate a 

 few of the more familiar examples of the family. 

 Our largest and in some respects most inter- 

 esting species belong to the genus Rhyssa. The 

 females of this genus are remarkable for the length 

 of their ovipositors, which frequently measure 

 three or four inches. These insects are parasitic 

 upon wood-boring larvaa, and especially those of 

 the genus Sirex. Both sexes may be seen flying 

 about trees infested by Sirex, and the females are often found with their long oviposi- 

 tors deeply sunken into the trunks of such trees in the act of laying their eggs in the 

 bodies of the wood-boring larvee. 



Fig. 642. — Microgaster nemororum, and a caterpillar covered witli 

 Microgaster larvae. 



Fig. 643. — Ophion macrurum. 



