8 BULLETIN 720, U. S. DEPARTMENT OF AGRICULTURE. 



cordata); of thalia, a plant related to the cannas; of saltbush, water 

 cro%vioots, water milfoil, and mermaid weed; water hemlock; and of 

 Spanish needle, or bur marigold. 



Animal Food. 



The animal food of the mallard duck though extremely varied 

 may be classed in five main groups: Insects, which constitute 2.67 

 percent of the total diet; crustaceans, 0.35; mollusks, 5.73; fishes, 

 0.47; and miscellaneous, 0.25 per cent. 



INSECTS (2.67 PER CENT). 



The mallard's attentions to insects are divided about equally 

 among beetles, bugs, and dragonflies, which together constitute 1.4 

 per cent of the total diet. All other insects make up 1.27 per cent. 

 As would be expected, the beetles eaten are mostly denizens of the 

 water. They include among others both larvae and adults of the 

 crawling water beetles (Haliplidae) , small spotted beetles, most often 

 seen among algse and other aquatic plants. Twenty different kinds 

 of predacious diving beetles (Dytiscidae) also were identified, both 

 adults and larvae being taken. The latter, so voracious that they 

 have earned the name water tigers, are very destructive to other 

 water-dwelling creatures and are a pest in fish ponds. Two partly 

 predacious groups, the water scavenger beetles (Hydrophilidae) and 

 the whirligig beetles (Gyrinids^) also are preyed upon by the mallard. 



Among, other beetles included in the dietary are ground beetles 

 (Carabidae), which are chiefly useful; and leaf beetles (Chrysome- 

 lidae) and weevils, which are injurious. Of the leaf beetles, a group 

 (Donacia) occurring in the mallard's habitat, and naturally fed upon, 

 live upon waterlilies. The adults rest on lily pads or skip about on 

 the water surface; the larvae live in tough cocoons on the lily stems, 

 from which they secure both food and oxygen. One of the weevils 

 identified in the food is the rice water weevil, a pest to cultivated rice. 



The bugs (Hemiptera) eaten by the mallard are practically all 

 aquatic forms. They include water boatmen (Corixidae), hundreds 

 of which have been found in a single stomach; back-swimmers 

 (Notonectidae) , water scorpions (Nepidae), giant water bugs (Belos- 

 tomatidae), creeping water bugs (Naucoridae), and water striders 

 (Veliidae and Gerridae) . All these bugs are predacious, but whether 

 they do more good than harm is a question, as many of them prey 

 upon small fishes. Besides the Hemiptera already mentioned, a 

 variety of other bugs occasionally are devoured by the mallard. 



Dragonfhes, or snake-feeders, are active and expert insects on the 

 wing, but in the younger stages they live in the water, where many of 

 them fall a prey to the mallard. No fewer than 100 dragonfly 

 njnnphs have been found in one mallard's gizzard, and from 30 to 40 



