115] 



FAUNA OF BIG VERMILION RIVER— BAKER 



17 



It will be noted that the nymph and larval forms of most species appear 

 coincident with the degree of sewage pollution. Chironomus and Libellula 

 are, seemingly, able to accommodate themselves to the contaminated or 

 polluted condition of the water in the neighborhood of St. Joseph. The 

 adult beetles, breathers of free air, are not affected directly by these un- 

 favorable conditions and occur in great abundance, even in the heavily 

 polluted parts of Salt Fork above St. Joseph. The Ephemerids occur for 

 the most part far down the stream where the water is at most only con- 

 taminated. The Neuroptera and Plecoptera are clean water forms and 

 were found only in the Middle Fork which does not carry sewage. These 

 are also to be found, probably, in the Big Vermilion below Middle Fork, 

 but no attempt was made to discover these animals when that part of the 

 stream was examined. 



Table I. Distribution of Insects 



