Rattlesnake - Garagarahebi (English spelling) rattlesnake

A general term for snakes in the Crotalus and Crotalus genera of the Viperidae family, Viperinae subfamily, Squamata order, Reptilia class. Venomous snakes known for having a special sound-producing organ at the end of their tails, distributed throughout most of the American continent, from southeastern Canada, the United States, and Central America to Argentina. There are 28 known species of Crotalus (and about 40 other subspecies), and three known species of Sistrurus , of which only the two Sistrurus species are found in South America. They are about 1.2 to 1.8 meters long, with the largest being the Eastern Diamondback Rattlesnake C. adamanteus , which is 2.4 meters long, and the smallest being the Carolina Rattlesnake S. miliarius , which is 60 centimeters long. The head is triangular and covered with fine scales, but in the Sistrurus genus, it is divided into large scales. Rattlesnakes have a distinctive sound-producing organ at the end of their tail, which is a sheath-like scale that is modified at the end of the tail, and one segment remains each time the snake sheds its skin. The older segments fall off one by one, starting from the tip. They make noise by standing upright and vigorously vibrating their tail. In the wild, most rattlesnakes have about eight segments, which is the most efficient way to make noise, but in captivity, some rattlesnakes have as many as 20 segments remaining, which reduces their efficiency. Baby snakes initially have a protrusion called a pre-button, and the first segment appears during the first molt, but rattlesnakes in the less differentiated genus Rattlesnake have a smaller sound-producing organ. There are several theories about why rattlesnakes make noise, including interspecies communication and preventing them from being crushed to death by raccoons, but the most likely theory is that it is a warning signal to alert predators of the presence of a poisonous snake. All rattlesnakes are highly venomous, and the larger ones are especially dangerous. They are ovoviviparous, giving birth to 20 to 60 young.

[Takahiro Matsui]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

爬虫(はちゅう)綱有鱗(ゆうりん)目クサリヘビ科マムシ亜科のうち、ガラガラヘビ属とヒメガラガラヘビ属に含まれるヘビの総称。尾端に特殊な発音器官をもつことで知られる毒ヘビで、カナダ南東部、アメリカ合衆国、中央アメリカからアルゼンチンに至るアメリカ大陸の大部分に分布する。ガラガラヘビ属Crotalusには28種（ほかに約40亜種）、ヒメガラガラヘビ属Sistrurusには3種が知られ、そのうち南アメリカにはガラガラヘビ属の2種だけが分布する。全長1.2～1.8メートルほどで、大はヒガシダイヤガラガラヘビC. adamanteusの2.4メートル、小はカロライナヒメガラガラヘビS. miliariusの60センチメートルである。頭部は三角形で細鱗に覆われるが、ヒメガラガラヘビ属では大形鱗に分かれる。ガラガラヘビの特徴である尾端の発音器官は、変形した尾端の鞘(さや)状の鱗(うろこ)が脱皮のたびに1節ずつ残されたもので、古い節は先端から順次脱落してゆく。発音は、尾部を立て激しく振動させることによる。自然界では尾節が8節ぐらいの個体が多く、もっとも効率よく音をたてるが、飼育下では20節も残って効率が落ちる個体がある。子ヘビには最初プレボタンとよばれる突起があり、最初の脱皮で第1節を生じるが、分化の進んでいないヒメガラガラヘビ属では発音器官が小さい。ガラガラヘビが発音する理由として、種間のコミュニケーション、ヤギュウによる圧死の防止などの諸説があるが、毒ヘビの存在を天敵に知らせる警告信号というのが、適説と考えられる。すべて毒性が強く、とくに大形種は危険である。卵胎生で20～60匹の子を産む。

［松井孝爾］

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