304 Insects and their Surroundings 



injected by the female insect with the egg (179)- It 

 is now generally believed, however, that the newly- 

 hatched grub, or possibly the advanced embryo itself, 

 sets up the irritation which leads to the formation of 

 the gall. Galls are specially characteristic of a family 

 of Hymenoptera, the Gall-flies (Cynipidae) ; and a 

 family of Diptera, the Gall-midges (Cecidomyidae). 

 But they are also produced by other insects, such as 

 certain Sawflies, some Scale-insects, and a few Beetles. 

 All parts of plants — leaves, branches, roots — may be 

 the seat of galls (3, 180, 182). 



Fungus-Eaters. — While the higher (flowering) 

 plants furnish most of the food for vegetable-eating 

 insects, the cryptogams are not neglected. As stated 

 above, seaweed is devoured by various insects of the 

 shore, and a considerable number of small Beetles 

 together with the grubs of many Flies and Midges find 

 their sustenance in fungi. The caterpillars in several 

 families of Moths feed on the lichens which hang in 

 festoons from the branches of trees, or cover the 

 surfaces of rocks. 



Scavengers. — Not fresh, growing vegetable tissues 

 only, but decaying vegetable matter is sought after by 

 insects as food. Damp, rotten refuse is found to be 

 inhabited by Beetles and their grubs as well as by the 

 maggots of Flies, while decomposing, rotten stems and 

 leaves — whose decay is often laastened by the attacks 

 of the insects mentioned in the preceding pages — 

 furnish nourishment to many species. The damp 

 earth formed by the waste of plant tissues is the food 

 of Springtails and other humble insects. From such 

 substances we pass by a natural transition to waste 

 animal matter on which multitudes of insects depend 

 for their livelihood. Many Beetles and their grubs, 

 and a host of Fly-maggots, live and feed in dung as 

 well as in the dead bodies of animals. The eagerness 



