
AQUATIC INSECTS OF FRESHWATER 

pair are wanting in some species. All are aquatic, the larve active, swim- 
ming among the water plants, crawling over the bottom, or burrowing 
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 life 
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 
ina film of air. The larval life is from two to three years, during which 
as many as twenty molts take place. Both the larve and nymphe of 
nearly allspecies feed on vegetal matter, diatoms, alge and conferve 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, Betis pygmea, Heptagenia pulchella, Fig. 213, and Siphlutus 
alternatus, some of which are extensively grown by fish breeders as a food 
for young fishes, especially the trout. 
Stone-Fiies belong to the order of Plecoptera, signifying plaited 
wing and referring to the folding of the hind wings. The body is long 
and flat,and of the four membranous wings the hind pairare slightly the larger 
and are folded on the abdomen when in repose. The antenne 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 larve require aerated water and will not survive in any numbers 
in stagnantor stillwater ponds and ditches. They are active andcarnivorous, 
feeding upon the young May-flies, soft-bodied Dipterous larve and upon 
vegetal matter. They have large flat heads, compound eyes anda flat body, 
which enables them to crawl under stones in the water. Usually they 
have long antenne and breathe by tracheal gills. The full-grown nymph 
is active and varies with different species from % to 1% 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 larve form one 
of the principal natural foods of the young trout, dace and other cold- 
water fishes. 
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