THE BUrXEKFLY 



59 



and the same leaf, the gaUs wiU be uiihke. Hence the char- 

 acteristic form of the gall is determined both by the species 

 of plant and l)y the species 

 of insect which lives in it. 

 It is interesting to collect 

 galls, watch for the emerg- 

 ing wasps, determine their 

 species, and thus get their 

 entire life history. The 

 gall-wasps are, on the whole, 

 injurious to agriculture. 



The plant-eating Hymen- 

 optera are extremely de- 

 structive pests. The young 

 are known as " slugs," from 

 their resemblance to the 

 true slugs, which are snail- 

 hke animals. They infest pear trees and rose bushes, leaving 

 scorched, dried leaves behind them.' Here also belong the 

 currant-worm and the sawflies (Figs. 64 and 6.5), which eat 

 leaves like caterpillars, but differ from them in having twelve 

 or sixteen prolegs instead of ten. 



1 See " The Pear Slug," in Circular No. 26, 2d Series, U. S. Department of 

 Agriculture, Division of Entomology. 



Fig. 65. — Egga of Nematus, a sawfiy on a 

 gooseberry leaf. Photo, by V. H. L. 



