244 



BULLETIN OF THE BUREAU OF FISHERIES. 



more in length, and of course any of the smaller species. The voracious Tropis- 

 ternus larvae frequently finish a long orgy of gluttony and cannibalism by passing 

 down the throat of an Anax nymph. Five half-grown Anax nymphs were captured 

 July 20, 1920, in pond 5D with Tropisternus larvae in their jaws. 



MITES. 



As a rule, beetle larvae are free from mites and pests of similar kinds, but 

 several larvae of Cybister jimbriolatus , captured in pond 5D in July, 1920, were each 

 infested with a single large mite, which had fastened to their leg and was distended 

 with blood. One such parasite could do but little harm, but if the number were 

 increased they might easily become a menace. 



HYDRA. 



While examining some Spirogyra and other filamentous algae for haliplid 

 larvae a considerable number of hydras were found. One of them had captured a 

 young larva of LaccopMlus froximus and was ingesting it. Of course, this might 

 have happened during the handling of the material, but the fact that the larva 

 had been paralyzed and was being eaten would show that small larvae are subject 

 to this peril if they once come within reach of the hydra. To this danger the slow- 

 moving haliplid larva, which feeds upon the algae, must be especially subject. 



ANTS. 



Ants of many species swarm everywhere around the margins of the ponds 

 and are always on the alert to seize any larvae they can overcome. Most of the 

 larvae are too large and active for them, but occasionally one of the smaller species 

 gets crippled and is then quickly pulled in pieces and devoured. 



TURTLES. 



Small turtles are apparently fond of both larval and adult beetles. Baker 

 (1916, pp. 231-233) reported the examination of the food contents of 15 specimens 

 of the painted turtle {Chrysemis picta). Three of them had eaten beetles including 

 both land and water species. In one 60 rum. long the wing cases of beetles formed 

 5 per cent of the food mass in the intestine. Another, 41 mm. long, had eaten 

 9 adult Hydrovatus pustulatus and 10 larvae of Peltodytes, forming 40 per cent 

 of its food. The third, 40 mm. long, had eaten 10 adult Hydrovatus pustulatus and 

 1 larva of Peltodytes, constituting 15 per cent of its food. 



FROGS. 



Two frogs are very common around the shores of the ponds — the leopard frog 

 (Rana pipiens) and the little cricket frog (Acris grillis). Many specimens of both 

 these frogs were examined and the contents of their digestive canal carefully listed. 

 Every one with a single exception had eaten either land or water beetles, sometimes 

 both, and while beetle larvae constituted but a small percentage of their food there 

 were enough to show that the frogs are dangerous enemies of the larvae. 



