Snakes! Especially visible in the warmer months, they're everywhere. Fortunately, you don't have to worry about the infamous Habu snakes of Okinawa, but Yakushima does have a bunch of other species, including poisonous snakes like the Japanese pit viper, called the mamushi. Here are some of the snakes that I've come across.
Tiger Keelback (Yamakagashi)
This beautiful snake is also poisonous, but most sources agree that you don't have to worry about them. The fangs, located in the back of the mouth, are good for subduing prey, but not very effective for defence. In fact, I have an acquaintance who was bitten when he accidentally grabbed one, but received no dose of poison! However, would-be predators know better than to attack the tiger keelback because, when threatened, glands on the back of its neck swell up to release the same toxin as the Japanese common toad. In fact, the tiger keelback gets this toxin by eating toads! I often spot this one sunning itself.
Burrowing/Forest Rat Snake (Jimuguri)
These are not known to be dangerous, but the juveniles have a coloration similar to the tiger keelback and I've had one take a defensive, striking stance as it backed away from me. The adults are much more drab, but the young ones are often spotted in the spring. The Japanese name reflects their use of rodent burrows.
Japanese Rat Snake (Aodaisho)
This is the snake that tends to freak people out because they often grow to be a couple meters long and they aren't exactly shy. Excellent hunters, they are respected for keeping rodent populations in check. They can be spotted both in the mountains and in fields outside of town.
Japanese Four-Lined Ratsnake (Shimahebi)
The majority of these guys that I've seen were victims of traffic, but apparently they're pretty common. Most of the ones I've seen are the blackish variety.
Asian/Japanese Keelback (Hibakari)
What can I say besides this is one cute little snake! When startled, they usually take an aggressive posture, raising their heads as if readying to strike. They appear so intimidating that supposedly people used to think they were poisonous, giving them the Japanese name, Hibakari, or "merely a day", as in, "merely a day left to live if you are bitten." But, in fact, they are quite harmless. I've spotted lots of these guys in early summer.
Erabu Sea Snake (Erabu Umi Hebi)
Most of these snakes enjoy sunny weather as much as tourists, and there are many more (non-poisonous) species in Yakushima that I haven't mentioned. So be on the lookout this summer and maybe you'll be lucky enough to spot one!