How to Identify the Olive-Headed Sea Snake (Identification Guide)

Key identifying features

The Olive-Headed Sea Snake (Hydrophis major) is a fully marine species recognized by the olive to olive-brown coloring concentrated on its head and forward body, which often contrasts subtly with a lighter or more patterned rear section.

Coloration & pattern

The head and neck typically show a solid olive, olive-brown, or grayish-olive tone, while the rest of the body may carry faint dark crossbands or blotches over a paler gray or tan background. In some individuals the banding is quite subdued, leaving the olive head as the most consistent identifying feature. The belly is generally pale and unmarked or lightly marked.

Head, eyes & scales

The head is moderate in size and only slightly distinct from the neck, covered in the smooth, uniformly olive-toned scales that give the species its name. Eyes are small with round pupils, typical of sea snakes adapted to underwater foraging. Body scales are smooth throughout, contributing to a sleek profile.

Size & body shape

Adults commonly reach 100 to 130 cm in length, with a moderately robust body that thickens somewhat toward the front third before tapering to a flattened, paddle-like tail used for swimming.

Range & habitat where you'll see it

This species is distributed across northern Australian coastal waters and parts of the western Pacific and Indo-Malay region, typically favoring soft-bottomed coastal habitats, estuaries, and turbid nearshore waters over sand or mud.

How to tell it apart from look-alikes

The distinctly olive head and neck, often more solidly colored than the rest of the body, is the clearest way to separate this species from other Hydrophis sea snakes with more uniform body coloration or bolder banding throughout. When banding on the body is faint or absent, the olive head remains a dependable identifying feature.