160 



BRANCH ARTHROPODA 



puddle is small, it may be filled up with less expense. If neither can be 

 done, then spraying with kerosene along the edges of the banks and the 

 surface of the water every two or three weeks should be resorted to. The 

 oil kills by contact many adults and larva? among the grass and weeds, and 

 by coating the surface of the water with a film of oil the " wiggle-tails " 

 are suffocated. Many females also are killed by this film of oil when they 

 return to the surface to deposit their eggs. All open barrels (Fig. 130) 

 and cisterns should be screened, so that the female mosquito cannot get to 

 the water to deposit her eggs. 



The gall-gnats (Cecidomyi'idoi) are the smallest flies, but their great num- 

 bers and their gall-forming habits make them great enemies of plants. 

 There are about a hundred species in the United States, most of which are 



vcLuceLiA INANS. 



VESPA VULCARIS. 



VOL *- BOMB 



BOM&US 



Fig. 132. Two cases of mimicry: flies resembling a wasp in the one, and a 

 bee in the other. (Romanes.) 



destructive to cultivated plants. The minute reddish or white eggs are 

 deposited on or in living plants, and the maggot-like larvae probably imbibe 

 their food through the skin. 



The Hessian fly belongs to this family. It is a tiny blackish midge which 

 lays its eggs (Fig. 131) in the sheaths of leaves some distance from the 

 ground. The larva lives between the base of the leaf and the main stalk 

 and feeds upon the sap of the growing wheat. There are four or five broods 

 a year, both spring and winter wheat being infested. It is estimated that 

 the ravages of this insect cost the farmers of this country $10.000,000 

 annually. Were it not for its natural enemies, a half-dozen hymenop- 

 terous parasites, it would soon take the whole crop of wheat, rye, and 

 barley. The chief remedies which the farmer can use are the late planting 



