Entomology of tlie Illinois River. 157 



FOOD RELATIONS OF THE GUOUFS TREATED. 



The plant-feeding aquatic caterpillars seemed to occur 

 wherever their food plants grew. They are pretty well 

 protected by their habits of concealment in cases or 

 between leaves, the Hydrocampa apparently being kept 

 in check largely by its hymeuopterous parasite. 



The sand-wasps (Bembecidse) and the spider-wasps 

 (Pompilida?) were frequently seen flying about. The 

 former provision their nests with flies; the latter 

 with spiders, which are themselves predaceous and abund- 

 ant along wet shores. The effect of the sand-wasps on 

 aquatic Diptera is presumably injurious, and that of 

 the spider- wasps beneficial. 



The larvge of soldier-flies (Stratiomyiidse) herein 

 treated seem to feed on minute plant life, Odontomyia 

 as a rule taking that on aquatic vegetation, and Strat- 

 iomyia that on wet muddy surfaces. Their tough skin 

 efficiently protects these species from insect enemies, in 

 both larval and pupal stages, and it is probable that 

 like the Hydrocampa, they also are kept in check 

 largely by their hymeuopterous parasites (Smicra). 

 MegiU'i maculata^ a coccinellid beetle, has been observed 

 feeding on the eggs. I do not know of their being eaten 

 bv fishes. 



The larvae of horse-flies (Tabanidse), except possibly 

 the little Chrysops larvae, are active and rapacious. 

 They apparently do not attack operculate univalves^ 

 but are known to eat those in which the opening of 

 the shell is not protected by an operculum. 1 have not 

 noticed, however, that they have any preference for 

 these. They did not attack the blue earthworm {Sj>"r- 

 ganophilus eiseni) — so abundant in their usual habitat. — 

 when placed in confinement with them. Breeding-c;iLe 

 experiments lead me to think that their chief food is 

 soft larvae. They are usually found in the light or 

 sandy substance of wet shores. Although crane-flies 

 (Tipulidae) oviposit freely in such places, their larvae 



