INTERRELATIONS OF INSECTS 309 



the beetles eat aphides, but also fungus spores and pollen in 

 large quantities. Though Lepidoptera are pre-eminently phy- 

 tophagous, the larva of Feniseca tarquinius is unique in feeding 

 solely upon plant lice, particularly the woolly Schizoneura tes- 

 scllata of the alder. Among Diptera, Asilidse, Midaidae, 

 Therevidae and Empididae are the chief predaceous families. 

 Asilidae ferociously attack not only other flies, but also beetles, 

 bumble bees, butterflies and dragon flies; as larvae they feed 

 largely upon the larvae of beetles. Many of the larvae of 

 Syrphidae prey upon plant lice, and the larvae of Volucella feed 

 in Europe on the larvae of bumble bees and wasps. Of 

 Hymenoptera, the ants are to a great extent predaceous, 

 attacking all sorts of insects, but particularly soft-bodied 

 kinds; while Vespidae feed largely upon other insects, though 

 like the ants, they are fond of the nectar of flowers and the 

 juices of fruits. 



Parasitic Insects. Though very many insects occur as 

 external parasites on the bodies of birds and mammals, very 

 few occur as such on the bodies of other insects; one of the 

 few is Braula caca, a wingless dipteron found on the body 

 of the honey bee. 



A vast number of insects, however, undergo their larval 

 development as internal parasites of other insects, and most 

 of these parasites belong to the two most specialized orders, 

 Diptera and Hymenoptera. 



The larvae of Bombyliidae feed upon the eggs of Orthop- 

 tera and upon larvae of Lepidoptera and Hymenoptera. 

 Tachinidae are the most important dipterous parasites of other 

 insects and lay their eggs most frequently upon caterpillars; 

 the larvae bore into their victim, develop within its body, and 

 at length emerge as winged insects. These parasites often 

 render aw important service to man in checking the increase 

 of noxious Lepidoptera. 



The great majority of insect parasites many thousand 

 species belong to the order Hymenoptera, constituting one 

 of the primary divisions of the order. They are immensely 



