How to Identify the Japanese Mamushi (Identification Guide)

Key identifying features

The Japanese mamushi (Gloydius blomhoffii) is a small, thick-bodied pit viper identified by a series of dark-edged, circular or oval blotches down the back on a reddish-brown or grayish background, along with a relatively short tail and small triangular head.

Coloration & pattern

Base coloration is typically reddish-brown, tan, or grayish, marked with a row of dark brown or blackish blotches, often circular or ellipse-shaped with paler centers, running down the length of the back. The pattern can appear somewhat coin-like or chain-like along the sides. The belly is pale with dark mottling.

Head, eyes & scales

The head is triangular but modest in size relative to the body, distinct from the neck, with heat-sensing pits between the eye and nostril. Pupils are vertically elliptical. Scales are keeled, giving a slightly rough appearance.

Size & body shape

This is a small pit viper, usually 45 to 60 cm (about 18 to 24 inches) long, occasionally slightly larger, with a stout, thick body relative to its length and a short tail.

Range & habitat where you'll see it

The Japanese mamushi is found throughout much of Japan (excluding some southern islands) as well as parts of the Korean Peninsula and nearby regions, inhabiting grasslands, rice paddies, forest edges, and rocky hillsides, often near water.

How to tell it apart from look-alikes

Its small size, stout build, and rounded, coin-like blotch pattern distinguish it from other Asian pit vipers, which tend to be larger or have more angular blotches. Within Japan, it is one of the most commonly encountered venomous snakes and often confused only with harmless rat snakes lacking the triangular head and pit organs.