254 , ENTOMOLOGY 



both as larvae and imagines, Gyrinidae subsist chiefly 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. tri- 

 angularis, for example, Fig. 227) feed largely if not entirely upon vegetation. 

 Of terrestrial Coleoptera, the tiger beetles (Cicindelidae) are strictly pre- 

 daceous 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 seg- 

 ment 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 predaceous; these " running beetles" both as larvae and adults 

 easily overtake and capture other terrestrial insects. The Carabidae, 

 however, are by no means exclusively carnivorous, 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; Calosoma, however, 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 unusually abundant they form a correspondingly large 

 percentage of carabid food, the increase being compensated by a dim- 

 inution in the amount of vegetable food taken (Forbes). Coccinellid 

 larvae (excepting Epilachna, which eats leaves) feed almost entirely upon 

 plant lice and constitute 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 phytoph- 

 agous, the larva of Feniseca tarquinius is unique in feeding solely upon 

 plant lice, particularly the woolly Schizoneura tessellata of the alder. 

 Among Diptera, Asilidae, 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 partic- 

 ularly 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 



