COLEOPTERA 



i39 



These beetles are very voracious. They destroy not only other in- 

 sects, but some of them will attack larger animals, as small fish. When 

 kept in aquaria they can be fed upon any kind of meat, raw or cooked. 

 They fly from pond to pond, and are often attracted to light at night. 

 Many of the species make sounds, both under the water and in the air. 

 In some cases this is done by rubbing the abdominal segments upon the 

 elytra; in others, by rubbing the hind legs upon a rough spot on the lower 

 side of the abdomen. 



The females deposit their eggs singly in punctures in the tissues of 

 living plants. The larva? are 

 known as water-tigers, be- 

 cause of their blood-thirsti- 

 ness. They are elongated, 

 spindle-form grubs (Fig- 233). fig. 233. 



The head is large, oval or rounded, and flattened; the mandibles are 

 large and sickle-shaped; in each there is a slit-like opening near the tip; 

 from this opening a canal leads along the inner surface to a basal opening 

 on the upper surface, which communicates with the corner of the mouth 

 when the mandible is closed. The mandibles are admirably fitted for 

 holding prey and at the same time sucking juices from its body. The 

 thorax is furnished with six well-developed legs. The abdomen is termi- 

 nated by a pair of processes; at the tip of the abdomen there is a pair of 

 large spiracles, which the larva protrudes into the air at intervals, in 

 order to breathe. 



When a larva is fully grown it leaves the water, burrows into the 

 ground, and makes a round cell, within which it undergoes its transforma- 

 tions. The pupa state lasts about three weeks in summer ; but the larva? 

 that transform in autumn remain in the pupa state all winter. 



This is the largest of the families of water-beetles; more than three 

 hundred North American species are known. 



The best way to obtain specimens is to sweep the vegetation growing 

 on the bottom of a quiet pool with a dip-net. 



The larger of our common species belong to Cybtster, 

 Dythcus (Fig. 234), and allied genera. 



The most common of the diving-beetles which are 

 of medium size belong to the genus Acilius. 



There are also common diving-beetles which are of 

 about the same size as the preceding, but which have 

 the wing-covers marked with numerous very fine trans- 

 verse striae; these belong to the genus Colymbetes. 



Of the smaller diving-beetles, measuring less than 

 I of an inch in length, many species can be found in 

 almost any pond. These represent many genera. 



Fig. 234. — A Dytis- 

 cus beetle. 



Family Gyrinid^e 



The II li irl i gig-beetles 



As familiar to the country rover as the gurgling of the brook or the 

 flecks of foam on its " golden-braided centre," "or the trailing ferns and 

 the rustling rushes on its banks, are these whirligigs on its pools. Around 

 and around each other they dart, tracing graceful curves on the water, 



