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ADAPTATIONS OF AQUATIC INSECTS 
Ease, versatility and perfection of adaptation are beauti- 
fully exemplified in aquatic insects. 
Systematic Position.—Aquatic insects do not form a sepa- 
rate group in the system of classification, but are distributed 
among many orders, of which Plecoptera, Ephemerida, Odo- 
nata and Trichoptera are pre-eminently aquatic. One third of 
the families of Heteroptera and less than one fourth those of 
Diptera are more or less aquatic. One tenth of the families 
of Coleoptera frequent the water at one stage or another, but 
only half a dozen genera of Lepidoptera. A few Collembola 
live upon the surface of water, and several Hymenoptera, 
though not strictly aquatic, are known to parasitize the eggs 
and larve of aquatic insects. 
The change from the terrestrial to the aquatic habit has been 
a gradual change of adaptation, not an abrupt one. Thus at 
present there are some tipulid larvee that inhabit comparatively 
dry soil; others live in earth that is moist; many require a 
saturated soil near a body of water and many, at length, are 
strictly aquatic. Among beetles, also, similar transitional 
stages are to be found. 
Food.—Insects have become adapted to utilize with re- 
markable success the immense and varied supply of food that 
the water affords: Hosts of them attack such parts of plants 
as project above the surface of the water, and the caterpillar 
of Paraponyx (Fig. 171) feeds on submerged leaves, espe- 
cially of Vallisneria, being in this respect unique among Lepi- 
doptera. Hydrophilid beetles and many other aquatic insects 
devour submerged vegetation. The larvee of the chrysomelid 
genus Donacia find both nourishment and air in the roots of 
aquatic plants. Various Collembola subsist on floating alge, 
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