SURROUNDINGS OF GROWING INSECTS 227 



In concluding this brief outline of insect-larvae parasitic 

 on other insects, mention may be made of certain minute 

 Hymenoptera which lay their eggs in the eggs of larger insects, 

 so that their larvae may feed on the contents. Anastatus bifas- 

 ciatus (Fig. 114 a), for example, is an egg-parasite of the 

 " Gipsy ' moth, and its tiny but stoutly-built larva (Fig. 

 114 b) feeds on the stored food-material of the egg, being 

 adapted for development in eggs before the formation of the 

 lepidopteran embryo has advanced. A little proctotrupid 

 fly (Schedius kuvanae), also lays her eggs in the "Gipsy' 

 eggs, but the Schedius larva develops in the unhatched cater- 

 pillar rather than in the unabsorbed yolk ; in some cases 

 Schedius acts the part of a secondary parasite to Anastatus, as 

 a larva of the latter has been observed within a shell of the 

 " Gipsy's " egg with three Schedius grubs feeding inside its 

 own body (Fig. 114 d). 



Among these parasites may be mentioned as of especial 

 interest the minute " fairy-flies " (Mymaridae) with delicately- 

 fringed wings, some of which dive under water, using their 

 wings as swimming-organs, and lay their eggs in the eggs of 

 dragon-flies within which the tiny larvae feed. The mymarid 

 grub is said to devour the dragon-fly's egg in a few days, and 

 the whole life-history lasts only a fortnight, the imago coming 

 from the pupa enclosed within the host-eggshell, and swimming 

 with strokes of the oar-like wings up to the surface of the water. 



The mention of these tiny egg-parasites in connexion with 

 dragon-flies suggests some reference to the large number of 

 insects which in the larval as well as in the adult stages of their 

 life-history live by preying on weaker creatures, which they 

 catch and devour. The dragon-fly's larva (see pp. 44-9) is a 

 typically predaceous insect, that lurks concealed at the bottom 

 of its native pond or stream and stalks smaller larvae ; its 

 large size and the nature of its feeding activities differentiate it 

 sharply from a parasitic grub. Yet there are instances in 

 which it is not easy to decide whether a larva ought to be 

 regarded as a parasite or a beast of prey. We may take for 

 example the " digging wasps ' (Pompilidae and Sphegidae) l 

 belonging, like the ichneumonoids, to the Hymenoptera, but 



1 J. H. Fabre : " Souvenirs Entomolo^iques ". 1879-1905. G. W. and 

 E. G. Peckham : " On the Instincts and Habits of the Solitary Wasps". 

 Madison, Wisconsin, 1898. 



