WATER BEETLES IN RELATION TO PONDFISH CULTURE, 



247 



ANTS. 



It was noted above that the ants consumed the softer portions of the bodies of 

 beetle larvae, pupae, and adults which had been drowned inside the pupal chamber. 

 They are not content with being scavengers, however, and they frequently kill 

 both larvae and pupae. Their depredations would be much more numbrous were it 

 not for the fact that the beetle usually constructs its pupal chamber in earth too 

 moist for the ants. 



ENEMIES OF ADULTS. 



TURTLES. 



Mention has already been made on page 244 of certain adult beetles eaten by 

 turtles. A medium-sized snapping turtle was caught August 7, 1920, in one of the 

 ponds and placed in a large metallic tub. It disappeared over night but left behind 

 excreta containing 1 adult Hydrous triangularis, 2 Cyhister Jimhriolatus, 1 Dytiscus 

 Tiyhridus and 1 Tropisternus lateralis, these beetle remains constituting fully 50 per 

 cent of the excreta. 



BIRDS. 



McAtee and Beal (1912, p. 19) recorded the food of a horned grebe {Colymhus 

 auritus) as containing 23.3 per cent beetles, chiefly aquatic. Two little green herons 

 (Butorides virescens virescens Linn.) , shot at one of the fishponds in Fairport August 

 10, 1918, were examined and their stomach contents listed. Among other things 

 one had eaten an adult Hydrous triangularis, which formed 25 per cent of its food. 

 The other had eaten two Donacia adults and one Laccophilus maculosus, which 

 together formed 30 per cent of its food. 



The shoal water ducks must also be recorded among the more important 

 enemies of adult water beetles. In a paper by W. L. McAtee (1918) a summary 

 was given of the items of food identified in the stomachs of three species of mallard 

 ducks. Out of 2,398 stomachs examined Haliplidse were found in 25, Dytiscidae in 

 139, Gyrinidae in 9, Hydrophilidae in 99. This is a total of 272, a little more than 

 one-ninth of the whole number. What was said with reference to the common 

 mallard (McAtee, 1918, p. 8) may be taken as applying to all three species. 



The mallard's attention to insects is divided about equally among beetles, bugs, and dragonflies, 

 which together constitute more than half of the insect food. The beetles include both larvae and adults 

 of the Haliplidse, 20 different kinds of Dytiscidae, both adults and larvae, Hydrophilidae and Gyrinidae. 



A paper by D. C. Mabbott (1920) gave the items of food of seven species of 

 shoal water ducks. These contributed to the destruction of beetles in the following 

 manner : 



The most common Coleoptera [in gad wall stomachs] were water scavenger beetles (Hydrophilidae), 

 predacious diving bottles (Dytiscidae), ground beetles (Carabidae), leaf beetles (Chrysomelidae), and 

 weevils (Rhyncophora). * * *. Of the 362 birds taken during the fall and winter months only 23 

 had eaten beetles, and these never amounted to more than 4 per cent of the stomach contents. Of 11 

 ducklings taken in July, however, all but one had eaten beetles; in three instances these amounted to 

 15 per cent and constituted 7.09 per cent of the food of all [p. 9]. 



