Usually not aggressive, they bite if provoked. There are about a dozen species.
The habu is viewed as having migrated to Okinawa over a prehistoric land bridge connecting the island to China. If one is bitten, it is excruatingly painful; fatalites were once common on Okinawa, though the snake has been controlled on Ryukyu islands that comprise Okinawa prefecture since the introduction of the mongoose from India in 1910. Different variants of the snake live on different islands of Okinawa prefecture.
The habu does not properly hibernate (in Okinawa, at least) during the winter, but is more active from April to late fall. Okinawa residents are advised to keep weeds trimmed and avoid loose lumber close to their dwellings, or anything in general that attracts the rodents upon which they feed.
In Okinawa after the American occupation, when A-12s (and the later the SR-71 Blackbird) planes were flown out of Kadena Air Base, Okinawa, the locals thought the strange and dangerous-looking planes looked like a habu, dubbing it the Habu.
The habu was a prime player in a silly Japanese kiddie story called Miki the Mongoose. Bottles of (very expensive) "Habu wine" are widely sold in Naha, the capital of Okinawa prefecture; the habu venom present in the wine (along with a dead snake on the bottom) is reputed to increase male virility.