REPORT ON MOSQUITOES. 87 



portunity offers ; simply that they do not form an important 

 check. 



On the other hand, the larvae of the Dytiscids, or diving- 

 beetles, also called water tigers, are among- the greatest enemies 

 of mosquito life, and I am inclined to attribute the comparative 

 freedom from mosquitoes in the hilly section of the State very 

 largely to these insects. Dr. Johnson records an instance of 

 their effectiveness in his contribution to the report of 1902. 



" My observations were mainly confined to the ' water tiger,' 

 or larva of the large water beetle, Dytiscus. The ability of this 

 voracious creature to clear a pool of larvae was demonstrated 

 in the laboratory by several captive water tigers, all of them 

 young ones, about a centimeter (less than half an inch) in 

 length, which created havoc in some of the jars containing Culex 

 larvre. 



"An out-door demonstration was afforded by a small pool 

 about half a mile south of the North Arlington railway station, 

 between Schuyler avenue and the meadows. To all appearances 

 this pool, which was barelv ten feet across in July and gradually 

 diminished during the summer, possessed every condition for the 

 breeding of mosquitoes in great numbers. In contained no fish 

 and few water insects, with the exception of the Dytiscus larvae, 

 which seemed quite abundant. On July 26th, when first visited, 

 the pool was thoroug'hly examined, but yielded very few larv?e of 

 Culex and only two or three of Anopheles. 



"The pool was visited again early in August, but no larvj£ were 

 found; again August i8th, when a very few Culex were obtained. 

 In order to determine whether the ^^'ater was incapable of sup- 

 porting larvae, ten large and medium-sized Anopheles larvae were 

 placed in a sample of it brought to the Laboratory. The next 

 morning there were only eight. The loss of two was accounted 

 for by the presence of a very small water tiger, which had been 

 accidentally left in the jar, and at the moment of discovery had a 

 larva in his jaws. After removal of the enemy, seven of the larvae 

 completed their development, and all had pupated on the 25th, 

 thus proving that the water was by no means unsuitable for the 

 development of Anopheles. The pool was visited again Septem- 

 ber 6th. Both Culex and Anopheles larvae were found in fair 

 abundance, but no^ Dytiscus larvae were seen. The absence of the 

 voracious water tigers, owing presumably to metamorphosis, 

 seems the most plausible explanation of the gTeat increase in the 

 number of mosquito lan^ae." 



No one who has not actually seen these tigers at work can ft>rm 

 any idea of their voracity. They rarely seem to be at rest, and 

 when they do it is usually more a waiting for the approach of 



