Japan with its humid climate is paradise for reptiles and has 47 species of snakes alone. Most of the snake species are not poisonous but feed on amphibians and rodents or other small mammals. The most commonly encountered one (and a very large one) is the Japanese Rat Snake or Aodaisho (Elaphe climacophora) (see photo here and closeup photo here) is harmless.
Aodaisho rat snake can reach lengths of 3½ meters. Interesting trivia: In Iwakuni City, Yamaguchi Prefecture, is the only place in the world where there is an entire natural population of albino rat snakes. They are white snakes pure white and have pink eyes.
There are three main types or classes of poisonous snakes below however, you should beware of.
Do not disturb: A venomous Japanese Mamushi warms itself between hunting small rodents and birds. © IMAGES OF JAPAN
Japanese Mamushi (Gloydius blomhoffii)
Illustrated warning boards of the Japanese Mamushi can sometimes be seen on nature trails. The Japanese Mamushi is most commonly warned of because it is Japan’s most dangerous snake. The mamushi’s bite causes tissues to liquify…you literally end up with an injury that leaves a chunk of your body missing. The mamushi hunts for food by day as well as at night. They have heat sensitive glands that allow them to locate birds and mammals in the dark. They hunt frogs and small mammals and have fangs that inject poison like hypodermic needles. However, the snake is shy so people who get bitten are probably those startle the snake accidentally.
The Habu (Trimeresurus flavoviridis) is a venomous pitviper of light olive or brown ground color overlaid with elongated dark green or brownish blotches that is found on some of the Okinawa Islands (Okinawa and Amami Islands). It is often found between the woods and the palm fields and on rock walls and in tombs and caves. The blotches have yellow edges, sometimes contain yellow spots, and frequently fuse to produce wavy stripes. The belly is whitish with dark coloring along the edges. Amami Islanders have a high incidence rate of being bitten by the snake but fatalities are rare (only three known cases). The longest known habu snake measured 225 centimeters and was displayed at the Okinawa Worlds’ Habu Park.
According to naturalist Mark Brazil, summer is “a great time of year to seek out warmth-loving reptiles, and the further south you are in Japan the more species you have to look for, with Okinawa being best blessed”…. Basking in sunshine is a favorite activity of many species of snakes, but for some reason members of the family Viperidae particularly enjoy it. They become drowsy in the sun, or perhaps it’s because they have become cool and then sluggish that they move into the sun to warm themselves and become active. Either way, exposed banks and roadsides are ideal places to find them, whether the Habu and Himehabu snakes of the Ryukyu Islands or the Mamushi, which ranges from Yakushima Prefecture north to Hokkaido.”
Yamakagashi
Beware also, the largest of Japanese snakes, the Japanese Keelpack or Japanese Grass Snake (Yamakagashi) may appear to be the most docile of snake … it is widely to believed to be non-poisonous but the snake was known to have killed someone in the ’80s. The snakes deliver their venom via some small back teeth, and have to actually chew on the victim to deliver the poison. The snakes like cobras flatten their necks when threatened.
There is another family of poisonous snakes one is not usually alerted to — because they are usually found in the sea – to find out more, see: ELAPIDAE(Cobra)
Below links to all the poisonous snakes that can be found in Japan.
References:
‘Spotted snakes, with double tongue’ Japan Times, Sun, Jun 21. 2009
Snakes of Japan This website introduces all the snake species found in Japan
Habu a Snake to be Respected Articlesabase
Hour of the Habu By Kotoko Chinen (Weekly Japan Update, 1999-11-10)
Poisonous snakes (Green Gables website)
Reptiles (Natural-Japan website)
Snakes, frogs, lizards and turtles in Japan
NATURE IN JAPAN 
Are Mamushi common around Kochi Prefecture.
Mamushi can be found in Kochi ken, they are found everywhere in Japan really. But they are mostly found in highlands and mountainous areas. They aren’t active in the daytime or in high temperatures, and so are mostly around the shade under rocks. Snakes like cold places, holes and drains.
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We have rellttesanke her in grants pass Oregon and gardensanke