In those snakes more than 700 millimeters in length, males outnumber females three to one. The maximum age of cottonmouths in nature is unknown, but one has been kept in captivity for more than 18 years. Allometric growth is striking in cottonmouths. The head and tail are proportionately longer in young individuals than in adults; and in males the tail is, on the average, slightly longer than in females of the same size. Shedding of the skin provides for growth and wear in snakes. The young shed within a few days after birth and generally shed more frequently than adults. Frequency of shedding depends mostly on amount of food consumed, and there is some evidence that injuries on the head and neck increase the frequency of shedding. Before shedding, the eyes become cloudy for about five and one-half days, then clear up again for about four days before the skin is shed. The food of cottonmouths consists mainly of small vertebrates and occasionally invertebrates that are found near water. Fish, amphibians, and reptiles make up nearly 70 per cent of the diet. Carrion is also eaten and cannibalism occurs occasionally. Food is obtained by lying in ambush or by active searching. The young are known to lure their prey within striking range by waving their yellow tails in a manner suggestive of writhing grubs. The method of obtaining prey differs according to the kind of prey. Generally, cottonmouths retain their hold on fish or frogs but release mice and larger prey after delivering a bite. The major causes of mortality of cottonmouths are obscure. Predators are known to include alligators, indigo snakes, king-snakes, largemouth bass, and blue herons; there are probably numerous others. Heavy parasitic infestations were found among the snakes examined. Snake mites, _Ophionyssus natricus_, became increasingly abundant on almost all captive snakes in April and May of 1963. Lung flukes (_Ochetosoma_ sp.) were in 16 of 20 captive snakes, and many preserved specimens contained nematodes (_Kalicephalus_ sp.) in the stomach and/or tapeworms (_Ophiotaenia_ sp.) in the intestine. Although parasitic infestation causes discomfort and may lower resistance to other detrimental factors, it is difficult to attribute death to the effect of any particular kind of parasite. Miscellaneous causes of death of some captive snakes also were discussed.