FIELD BOOK OF PONDS AND STREAMS 



Collecting, aquarium study. — Diving beetles forage in the 

 populous shallows near shore and are easily collected there 

 by sweeping the plants with a net. Both larvae and adults 

 are interesting aquarium animals but they must be kept well 

 supplied with live food. Harris kept an adult Dytiscus 

 "three years and a half in perfect health in a glass vessel 

 filled with water, supported by morsels of raw meat. " 



t 



Fig. 206. — A common medium-sized diving beetle, 

 Aciliiis: i, adult; 2, larva (from Wilson). 



Acilius. — This is the commonest of the medium-sized diving 

 beetles. The adults (Fig. 206) are about one inch long, dull 

 3^ellowish-brown with yellow margins on the thorax and 

 wang-covers, each of which bears four furrows. The larvae 

 (Fig. 206) are easy, graceful swimmers. When they are 

 resting below the surface the body is curved in a crescent, 

 usually around a plant stem, and whenever they let go they 

 are buoyed upward, tail foremost, by the air within their air 

 tubes. Sooner or later they hang head down with tails thrust 

 through the surface film. 



In the larvas of Acilius the prothorax is considerably longer 

 than wide. 



Coptotomus. — Unlike Acilius this larva (Fig. 207) is not de- 

 pendent upon air and it is always found prowling on the bot- 



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