Asian Vine Snake

The horizontal, keyhole- or dumbbell-shaped pupil of Ahaetulla vine snakes is found in no other snake genus, and it is part of a package for accurate forward vision. Running along each side of the snake's long, pointed snout is a shallow groove, and the snake can angle its eyes so that the fields of view of the two eyes overlap in a narrow strip directly ahead, looking down these grooves like the sights of a rifle. The unusual pupil shape improves the sharpness and depth information of that forward strip. The result is genuine binocular, stereoscopic vision, which is rare among snakes and gives the vine snake a much better sense of exactly how far away a target is.

With patience, camouflage, and an accurate strike. The snake lies motionless along a branch or among foliage, its thin green body indistinguishable from a vine, sometimes swaying slightly to match the movement of surrounding leaves, and waits for a lizard or tree frog to come within range. Because its forward binocular vision lets it judge the distance to the prey precisely, it can then launch a fast, well-aimed strike rather than a hopeful lunge, seize the lizard, and chew its mildly venomous saliva into the wound from the grooved fangs at the back of its mouth. The venom weakens and quietens the struggling prey while the snake works it into position to swallow.

It is technically venomous but effectively harmless to people. Vine snakes are rear-fanged, with grooved teeth at the back of the upper jaw and a mild venom adapted for subduing small lizards and frogs. To envenomate a person they would have to get those back teeth engaged and chew for a while, which almost never happens, and the recorded effects of the rare bites that do inject venom are limited to local pain, tingling, mild swelling, and occasionally numbness that resolves within a day or two. There are no serious or fatal cases. The snakes are not aggressive; their defence is to hide, and if that fails, to bluff with an inflated neck and gaping mouth.

They are kept, and they are among the more commonly available rear-fanged colubrids, but they are considered an intermediate to advanced species. They are highly strung and fast, dislike handling, need a tall, densely planted, humid enclosure with many thin branches and good ventilation, and are strongly diurnal and visual, so they need proper lighting. The biggest challenge is diet — wild vine snakes eat mostly lizards, and many individuals, especially wild-caught imports, refuse rodents entirely, so keepers may need a supply of anoles or other lizards, or must work to convert the snake to scented mouse pups. Captive-bred animals are calmer and feed more readily and should be sought where possible.