AQUATIC INSECTS 



able to live from an hour to an hour and a half in ninety -five 

 per cent alcohol. This larva is about three eighths of an inch 

 long. 



Fig. 214. — Tropisternus lateralis: i, larva (after 

 Wilson); 2, adult. 



Tropisternus. — This medium-sized shiny black beetle (Fig. 

 214) abounds in nearly all beetle habitats, where it is often 

 by far the commonest kind to be found. The adults are 

 adepts at every kind of locomotion except jumping and ailb 

 thus agile even on land. They are thorough vegetarians, 

 living entirely upon algas. 



Wilson characteristizes the larva of Tropisternus lateralis 

 (Fig. 214) as follows: "Its exertions when eating demand a 

 constant air supply, and it usually seizes its, prey and swims 

 to the nearest water plant. It then backs up the stem, 

 dragging its prey after it until it can thrust its abdomen above 

 the surface. It can thus eat and breathe at the same time, 

 and it is engaged in doing both nearly all the time. ... It 

 is the very personification of voracity and gluttony and will 

 eat any kind of an insect or larva that it can overpower." 

 Usual length, one half inch. 



Riffle-beetles, Family Psephenidae. — The lar\^as of riffle- 

 beetles live in rapid currents, a habit which is rare among 



277 



y. 



