Aquatic Insects 195 



INSECTS 



This is the group of animals that is numerically 

 dominant on the earth today. There are more known 

 species of insects than of all other animal groups put 

 together. The species that gather at the water-side 

 give evidence, too, of most extraordinary abundance of 

 individuals. Who can estimate the number of midges 

 in the swarms that hover like clouds over a marsh, or 

 the number of mayflies represented by a windrow of 

 cast skins fringing the shore line of a great lake? The 

 world is full of them. Like other land animals they are 

 especially abundant about the shore line, where condi- 

 tions of water, warmth, air and light, favor organic 

 productiveness . 



Nine orders of insects (as orders are now generally 

 recognized) are found commonly in the water. These 

 are the Plecopte ra or stoneflies; the Ephemerida or 

 mayflies; the O donata or dragonflies and damselflies; 

 the Hemiptera or water bugs ; the Neuroptera or net- 

 wingect insects^ the Trichoptera or caddis-flies; the 

 ■Lepidoptera or moths ; the »Coleop_tera or beetles ; and 

 the Diptera or true flies. These, together with the 

 Thysanura or springtails, which hop about upon the 

 surface of the water in pools, and the Hymenoptera, 

 of which a few members are minute egg-parasites and 

 which, when adult, swim with their wings, represent 

 the entire range of hexapod structure and metamor- 

 phosis. Yet the six-footed insects as a class are 'pre- 

 dominantly terrestrial. It is only a few of the smaller 

 orders, such as the stoneflies and the mayflies, that 

 are wholly aquatic. Of the very large orders of moths, 

 beetles and true flies only a few are aquatic. 



Aquatic insects are mainly so in their immature 

 stages; the adults are terrestrial or aerial. Only a few 

 adult bugs and beetles are commonly found in the 



