INTERRELATIONS OF INSECTS 271 



upon disabled insects, but occasionally eat plant substances, and 

 Hydrophilidae as larvae catch and devour other insects, though some 

 of the beetles of this family (H. triangularis , for example, Fig. 229) feed 

 largely if not entirely upon vegetation. Of terrestrial Coleoptera, the 

 tiger beetles (Cicindelidae) are strictly predaceous upon other insects. 

 The Cicindela larva lives in a burrow in the soil and lies in wait for 

 passing insects; a pair of hooks on the fifth segment of the abdomen 

 serves to prevent the larva from being jerked out of its burrow by the 

 struggles of its captive. The large family Carabidae is chiefly predace- 

 ous; these " running beetles," both as larvae and adults easily overtake 

 and capture other terrestrial insects. The Carabidae, are by no means 

 exclusively carnivorous, however, for many of them feed to some extent 

 upon fungus spores, pollen, ovules, root-tips and other vegetable matter, 

 as Forbes has found; Harpalus caliginosus eats the pollen of the ragweed 

 in autumn ; Galerita janus eats caterpillars and occasionally the seeds 

 of grasses; but Calosoma appears to be strictly carnivorous, feeding 

 chiefly upon caterpillars and being in this respect of considerable 

 economic importance. As a whole, Carabidae prefer animal food, as 

 appears from the fact that when canker worms, for instance, are unusu- 

 ally abundant these form a correspondingly large percentage of carabid 

 food, the increase being compensated by a diminution in the amount 

 of vegetable food taken. (Forbes.) Coccinellid larvae (excepting Epi- 

 lachna, which eats leaves) feed almost entirely upon plant lice and con- 

 stitute one of the most effective checks upon their multiplication; the 

 beetles eat aphides, but also fungus spores and pollen in large quantities. 

 Though Lepidoptera are pre-eminently phytophagous, the larva of 

 Feniseca tarquinius is unique in feeding solely upon plant lice, particular- 

 ly the woolly Schizoneura tessellata of the alder. Among Diptera, 

 Asilidae, Midaidae, There vidae and Empididae are the chief predaceous 

 families. Asilidae (robber-flies) ferociously attack not only other flies, 

 but also beetles, bumblebees, 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 bumblebees and wasps. Of Hymenoptera, the ants are 

 to a great extent predaceous, attacking all sorts of insects, but particu- 

 larly 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 



