POOD HABITS OF MALLARD DUCKS. 9 



in others. Adult dragonflies were found in only one stomach. 

 These insects prey upon mosquitoes, but their nymphs destroy young 

 fish also, so that on the whole they are of no pronounced economic 

 benefit. 



Most of the other insects eaten by the mallard are more or less 

 aquatic in habits. For instance, the flies (Diptera) eaten are chiefly 

 those having aquatic larvae, and it is the larvse that are usually 

 obtained. These include craneflies, mosquitoes, gnats, horseflies, 

 soldierflies and flowerflies. Seven adult mosquitoes (Culex restuans) 

 were found in one mallard's' gizzard. Dr. Samuel G. Dixon, Health 

 Commissioner of Pennsylvania, commends the mosquito-destroying 

 capacity of the mallard. He writes : ^ 



After trying the ability of fish to devour larvae and pupae of mosquitoes, with varied 

 success, I built two dams near together on the same stream, so that each would have the 

 same environment for the breeding of mosquitoes. Each covered nearly 1,400 square 

 feet. In one twenty mallard ducks, Anas platyrhyncha, were permitted to feed, while 

 the other was entirely protected from waterfowl, but well stocked with goldfish, 

 Carassius auratus, variety americanus. 



The one in which the ducks fed was for several months entirely free from mosquitoes, 

 while the pond protected from ducks and stocked with fish was swarming with young 

 insects in different cycles of life. 



To the infested pond ten well-fed mallard ducks, Anas platyrhyncha, were then ad- 

 mitted , and as they entered the pond they were first attracted by the larval bactrachians , 

 tadpoles. They, however, soon recognized the presence of larvae and pupae of the 

 mosquito and immediately turned their attention to these, ravenously devouring 

 them in preference to any other foodstuff present. At the end of 24 hours no pupae 

 were to be found and in 48 hours only a few small larvae survived. The motion of the 

 water, made by the ducks, of course drowned some of the insects — what proportion 

 can not be estimated. 



For some years I have been using ducks to keep down mosquitoes in swamps that 

 would have been very expensive to drain, but I never fully appreciated the high degree 

 of efficiency of the duck as a destroyer of mosquito life until the foregoing test was 

 made. 



Mayflies, stoneflies, and caddisflies also are consumed, usually as 

 larvse. More than 200 caddisfly larvae have been obtained from a 

 single stomach. Caterpillars, including an aquatic form which lives 

 in nests made of duckweed, occasionally are disclosed by stomach 

 examinatioUo 



The other insects eaten include a few ants and other. Hymenoptera, 

 Orthoptera and their eggs, and bird lice (Mallophaga) . The last- 

 named undoubtedly are obtained from the bird's own body. That 

 mallards at times feed extensively upon grasshoppers was observed 

 particularly during outbreaks of the Rocky Mountain locust, when 

 from 12 to 49 of these insects were found in various stomachs by 

 Prof. Samuel Aughey.^ 



1 Joum. Amer. Med. Assn., LXin, no. 14, p. 1203, Oct. 3, 1914. 



2 First Ann. Kept. U. S. Ent. Conxm., Appendix H, p. 58, 1877. 



64336°— 18— Bull. 720 2 



