Tzuchinoko ("straw-bat snake") is the most common out of over 40 names used to refer to a possible crotalid snake inhabiting mountainous areas of three of the islands of Japan - Honshu, Kyushu, and Shikoku.  The snake is also said to be found on the Korean Peninsula, and it is also rumored to dwell in New Guinea.

The Tzuchinoko is a fairly small snake, only 2-3 feet in length.  The snake is covered with large scales, and has large eyes.  The eyes are surmounted by what are often called ears or horns.  Coloration of the animal is generally agreed upon as a black or rust color above, with the belly a bright orange; also, it seems to have a distinctive "chestnut tree flower"-like odor about it.

The serpent is rumored to be able to move in a straight line, as opposed to the meandering of many snakes.  It supposedly swims quite well, is reputed to be quite venomous, some even reporting its ability to spit its venom.  The snake is also said to make sounds - whistles, hoots, snores, or moans.  Some also claim that it can leap (a common attribute of serpents), and in a parallel to the American hoop snake myths, some even claim that it can roll itself into a hoop and roll down hillsides.

The Tzuchinoko has long been rumored to exist in Japan, but most specific reports have come from the last century.  Dethier and Dethier-Sakamoto reproduce several of these eyewitness reports in their 1987 article.

An account dating from the late 1950s is particularly striking.  M. Kyuzo, working in his fields near Hashimoto, heard a loud noise and turned to see a large, black object rolling down the hillside.  The object disappeared into a canal, and Kyuzo arrived at the canal in enough time to see the object unroll, make a vertical leap, and disappear.

Another account from 1970, when a couple walking near Mt. Tojikimi saw a Tzuchinoko, which they at first mistook for a tree branch.  The snake quickly moved off down a path.   The couple said it was large, with a short tail and large, brownish spots.   They thought that the shape of the snake's body was more triangular than circular.

Several of the accounts concerned captured specimens, including one from World War II, when a M. Foujiwara saw a captive snake near Kyoto.  In June of 1969, M. Tokutake captured a snake which he said was distinctly different from the mamushi, or Halys viper (Agkistrodon halys). As he approached the reptile, it looked at him, baring its teeth and flashing its tongue.  It leapt at Tokutake, who quickly managed to capture the snake with the aid of a forked stick. After several days, he supposedly ate the snake, commenting on its double backbone.

Dethier and Dethier-Sakamoto believe that the tzuchinoko can be identified as a member of the Viperidae (true vipers) or Crotalidae (pit vipers) family on the basis of many physical characteristics shared with these snakes.  More specifically, they believe it to be a member of the Agkistrodon genus of crotalids (which includes such snakes as the copperhead and cottonmouth), although they also suggest the possibility of a foreign species introduced to Japan from mainland Asia.