88 AGRICULTURAL EXPERIMENT STATION. 



their prey. Nothing- seems to satisfy their hunger, and I lost a 

 fine specimen, which I had hoped to carry to maturity, because 

 the food supply once failed to last over night. Mr. Viereck noted 

 specimens in one of his experiment ponds, and in confinement one 

 good-sized example killed or devoured 434 wrigglers in two days. 

 They are quite as effective as fish during their period of activity ; 

 but in very early spring and in late summer, when the species is 

 in either the eg-g or pupal stage, the mosquito larvae have a chance 

 to recover somewhat. The adult beetles, while they are also pred- 

 atory, are not nearly so voracious as the larvae. 



Anopheles as well as Cidex fall victim to the water tigers, and 

 where these are abundant, as they usually are in a hilly country 

 with plenty of spring-s and running water, mosquitoes stand very 

 little chance. In a flat country where temporary pools formed by 

 rains are more numerous and springs less plentiful the Dytiscids 

 are less numerous and hence less effective as a control. 



Figure 20. 



A whirligig beetle (i), and its larva (2), natural size. 



The whirligig beetles or Gyrinidce are also great mosquito 

 enemies and no Anopheles larva has a chance in any bit of water 

 inhabited by them. They are found along the eclges of ponds 

 and larger permanent bodies of water; in the eddies of larger 

 streams and sometimes in broad and rather rapid ditches. They 

 are black or bluish bronzed in color and by their habit of circling 

 about in swarms are readily recognized. Their surface habit 

 and their tendency to get near the edges make them especially 

 dangerous to Anopheles larvae, which absolutely fail to maintain 

 themselves within the range of these beetles. Their larv?s are 

 also predatory; but little is known of them and none have been 

 under direct observation by me. In ponds with shallow margins 

 with grass that bars the beetles but not the Anopheles larvae, a 

 little trimming of the edges is sometimes all that is necessary to 

 convert a source of danger into a safe area. 



