FOOD HABITS OF MALLARD DUCKS. 5 
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 larve, and it is the larve 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 larvee and pup 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 larve and pup 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 pupze 
were to be found and in 48 hours only a fewsmall larve 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. 
Maryflies, stoneflies, and caddisflies also are consumed, usually as 
larve. More than 200 ecaddisfly larve have been obtained from a 
single stomach. Caterpillars,including an aquatic form which lives 
in nests made of duckweed, occasionally are disclosed by stomach 
examination. 
The other insects eaten include afew 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 1 in various stomachs by 
Prof. Samuel Aughey.? 
1 Journ. Amer. Med. Assn., L_XITI, no. 14, p. 1203, Oct. 3, 1914. 
2 First Ann. Rept. U. 8. Ent. Comm., oer II, p. 58, 1877. 
64336°—18—Bull. 720-2 
