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''Agkistrodon piscivorus'' is a venomous snake, a species of pit viper, found in the southeastern United States. Adults are large and capable of delivering a painful and potentially fatal bite. When antagonized, they will stand their ground by coiling their bodies and displaying their fangs.〔(Cottonmouth Fact Sheet. ) ''Smithsonian Institution.''〕 Although their aggression has been exaggerated, on rare occasions territorial males will approach intruders in an aggressive manner.〔(epa.gov ) Wharton, C.H. 1969. The cottonmouth mocassin on Sea Horse Key, Florida. ''Bull. Florida St. Mus., Biol. Sci.'' 14 :227–272.〕 This is the world's only semiaquatic viper, usually found in or near water, particularly in slow-moving and shallow lakes, streams, and marshes. The snake is a strong swimmer and will even enter the sea. It has successfully colonized islands off both the Atlantic and Gulf coasts. The generic name is derived from the Greek words ''ancistro'' (hooked) and ''odon'' (tooth), and the specific name comes from the Latin ''piscis'' (fish) and ''voro'' (to eat); thus, the scientific name translates into “hooked-tooth fish-eater”.〔(Snakes-uncovered.com : Cottonmouth (''Agkistrodon piscivorus'') )〕 Common names include variants on water moccasin, swamp moccasin, black moccasin, cottonmouth, gapper, or simply viper.〔Wright AH, Wright AA. 1957. ''Handbook of Snakes of the United States and Canada''. Ithaca and London: Comstock Publishing Associates. (7th printing, 1985). 1,105 pp. (in 2 volumes) ISBN 0-8014-0463-0. (''Ancistrodon piscivorus'', pp. 916–925, Figures 263–265 , Map 65.)〕 Many of the common names refer to the threat display, where this species will often stand its ground and gape at an intruder, exposing the white lining of its mouth. Three subspecies are currently recognized, including the nominate subspecies described here. Its diet consists mainly of fish and frogs but is otherwise highly varied and, uniquely, has even been reported to include carrion. ==Description== This is the largest species of the genus ''Agkistrodon''. Adults commonly exceed in length, females grow smaller than males. Total length per one study of adults was .〔Kardong, K. V. (1982). ''Comparative study of changes in prey capture behavior of the cottonmouth (Agkistrodon piscivorus) and Egyptian cobra (Naja haje)''. Copeia, 337-343.〕 Average body mass has been found to be in males and in females.〔Vincent, S. E., Herrel, A., & Irschick, D. J. (2004). ''Sexual dimorphism in head shape and diet in the cottonmouth snake (Agkistrodon piscivorus)''. Journal of Zoology, 264(1), 53-59.〕〔Rainwater, T. R., Reynolds, K. D., Cañas, J. E., Cobb, G. P., Andersonv, T. A., McMurry, S. T., & Smith, P. N. (2005). ''Organochlorine pesticides and mercury in cottonmouths (Agkistrodon piscivorus) from northeastern Texas, USA''. Environmental toxicology and chemistry, 24(3), 665-673.〕 Occasionally, individuals may exceed in length, especially in the eastern part of the range.〔Campbell JA, Lamar WW. 2004. ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp. 1500 plates. ISBN 0-8014-4141-2.〕 According to Gloyd and Conant (1990), the largest recorded specimen of ''A. p. piscivorus'' was in length,〔Conant, 1975〕 based on a specimen caught in the Dismal Swamp region and given to the Philadelphia Zoological Garden. It should be noted, however, that this snake had apparently been injured during capture, died several days later and was measured when straight and relaxed.〔Gloyd HK, Conant R. 1990. ''Snakes of the ''Agkistrodon'' Complex: A Monographic Review''. Society for the Study of Amphibians and Reptiles. 614 pp. 52 plates. LCCN 89-50342. ISBN 0-916984-20-6.〕 Large specimens can be extremely bulky, with the mass of a specimen of approximately in length known to attain .〔Roark, A. W. (2003). ''Comparative genetic analysis in insular and mainland populations of the Florida cottonmouth, Agkistrodon piscivorus conanti'' (Doctoral dissertation, University of Florida).〕 The broad head is distinct from the neck, and the snout is blunt in profile with the rim of the top of the head extending forwards slightly further than the mouth. Substantial cranial plates are present, although the parietal plates are often fragmented, especially towards the rear. A loreal scale is absent. There are six to 9 supralabials and eight to 12 infralabials. At midbody, there are 23–27 rows of dorsal scales.〔 All dorsal scale rows have keels, although those on the lowermost scale rows are weak.〔 In males/females, the ventral scales number 130-145/128-144 and the subcaudals 38-54/36-50. Many of the latter may be divided.〔 Though the majority of specimens are almost or even totally black, (with the exception of head and facial markings), the color pattern may consist of a brown, gray, tan, yellowish-olive or blackish ground color, which is overlaid with a series of 10–17 dark brown to almost black crossbands. These crossbands, which usually have black edges, are sometimes broken along the dorsal midline to form a series of staggered halfbands on either side of the body. These crossbands are visibly lighter in the center, almost matching the ground color, often contain irregular dark markings, and extend well down onto the ventral scales. The dorsal banding pattern fades with age, so older individuals are an almost uniform olive-brown, grayish-brown or black. The belly is white, yellowish-white or tan, marked with dark spots, and becomes darker posteriorly. The amount of dark pigment on the belly varies from virtually nothing to almost completely black. The head is a more or less uniform brown color, especially in ''A. p. piscivorus''. Subadult specimens may exhibit the same kind of dark, parietal spots characteristic of ''A. contortrix'', but sometimes these are still visible in adults. Eastern populations have a broad, dark, postocular stripe, bordered with pale pigment above and below, that is faint or absent in western populations. The underside of the head is generally whitish, cream or tan.〔 Juvenile and subadult specimens generally have a more contrasting color pattern, with dark crossbands on a lighter ground color. The ground color is then tan, brown or reddish brown. The tip of the tail is usually yellowish, becoming greenish yellow or greenish in subadults, and then black in adults. On some juveniles, the banding pattern can also be seen on the tail.〔 Young snakes wiggle the tip of their tail to lure prey animals.〔(【引用サイトリンク】title=Cottonmouth )〕 This species is often confused with the copperhead, ''A. contortrix''. This is especially true for juveniles, but there are differences. ''A. piscivorus'' has broad, dark stripes on the sides of its head that extend back from the eye, whereas ''A. contortrix'' has only a thin dark line that divides the pale supralabials from the somewhat darker color of the head. The watersnakes of the genus ''Nerodia'' are also similar in appearance, being thick-bodied with large heads, but they have round pupils, no loreal pit, a single anal plate, subcaudal scales that are divided throughout and a distinctive overall color pattern.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Agkistrodon piscivorus」の詳細全文を読む スポンサード リンク
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