AQUATIC INSECTS OF FRESHWATER 



pair are wanting in some species. All are aquatic, the larvas active, swim- 

 ming among the water plants, crawling over the bottom, or burrowmg 

 into the banks. The nymph has small wing pads and in its transformation 

 floats on the surface of the water 'until the skin opens and the winged 

 insect emerges, when a molt takes place, followed by a second before the 

 adult stage is reached. In the final metamorphosis the mouth parts and 

 the alimentary canal are atrophied so that the insect cannot eat, its hfe 

 being very brief, often but a day; but when the atmosphere is moist, it 

 may survive several days. Flight principally takes place in the early 

 morning and evening hours. The eggs are deposited in the water either 

 by dropping on the surface or by the female creeping into the water incased 

 in a film of air. The larval life is from two to three years, during which 

 as many as twenty molts take place. Both the larvae and nymphas of 

 nearly all species feed on vegetal matter, diatoms, algae and confervae and are 

 harmless to young fishes. Though enormously numerous in individuals 

 there are comparatively few species, not more than eight or ten in the 

 Eastern section of the United States; of which the more common are 

 Ephemera varia, B^etis pygm>ea, Heptagenia pulchella. Fig. 213, and Siphlutus 

 ahernatus, some of which are extensively grown by fish breeders as a food 

 for young fishes, especially the trout. 



Stone-Flies belong to the order of Plecoptera, signifying plaited 

 wing and referring to the folding of the hind wings. The body is long 

 andflat,andof thefourmembranous wings the hind pair are slightly the larger 

 and are folded on the abdomen when in repose. The antennae are long 

 and threadlike and the mouth parts developed for biting. All the species 

 are aquatic and propagate in enormous numbers in almost every rapid 

 rocky stream, the female depositing 5000 to 6000 eggs on the water. 

 The larvae require aerated water and will not survive in any numbers 

 in stagnant or Stillwater ponds and ditches. They are active and carnivorous, 

 feeding upon the young May-flies, soft-bodied Dipterous larvae and upon 

 vegetal matter. They have large flat heads, compound eyes and a flat body, 

 which enables them to crawl under stones in the water. Usually they 

 have long antennae and breathe by tracheal gills. The full-grown nymph 

 is active and varies with different species from yi to \)4 inches in length, 

 their cast skins being common objects along the banks of streams. The 

 most generally distributed species are Leuctra tenella. Fig. 213, Pteronarays 

 proteus, Acroneuria abnormis, Isogenus frontalis and Perla ephyre. There 

 are no records of their being injurious to young fishes, and larvae form one 

 of the principal natural foods of the young trout, dace and other cold- 

 water fishes. • 



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