Hook-nosed Sea Snake

Fascinating facts about the Hook-nosed Sea Snake

• More than half of every sea-snake bite recorded in the Indo-Pacific comes from this species, and it accounts for the majority of the fatalities. That single snake is responsible for over 50% of all sea-snake envenomings, turning it into the region’s deadliest marine reptile. Its dominance in bite statistics reveals how a relatively small creature can shape human health outcomes in coastal communities.
• When the tide pulls back, these snakes can plunge to a depth of 100 m and linger underwater for up to five hours before surfacing for air. Such a dive time rivals many diving mammals, letting them hunt fish far below the surface. This endurance shows how sea snakes have evolved to exploit a three-dimensional oceanic hunting arena.
• A drop of just 1.5 mg of its venom can kill a human, while each bite delivers about 7.9–9.0 mg of toxin. Laboratory tests give an LD₅₀ of 0.1125 mg per kilogram of body weight, making its neurotoxic cocktail among the most potent known. These numbers explain why medical crews treat any encounter as a true emergency.
• Adult individuals stretch to a total length of 1,110 mm with an additional 190 mm tail, and their bodies bear 50–70 rows of keeled scales plus 230–314 ventral scales. The uniform dark-grey dorsal coloration contrasts with a whitish underside, while juveniles display striking black bands. Such precise measurements help scientists distinguish this snake from its dozens of sea-snake cousins.
• From the Arabian Gulf through the coasts of India, Sri Lanka, Bangladesh, Thailand, and Vietnam, this snake inhabits a swath of tropical Indo-Pacific waters, making it one of the most widespread sea snakes in the region. Its presence on both mainland coasts and offshore islands underscores its adaptability to varied marine habitats. This broad range explains why it encounters humans so frequently, driving its high bite incidence.

At a glance

About the Hook-nosed Sea Snake

The hook-nosed sea snake, Hydrophis schistosus, is a sleek, uniformly dark-grey marine reptile that glides through the warm waters of the tropical Indo-Pacific. Its head bears a distinctive rostral scale longer than it is broad, touching four shields, while the body is encircled by 50–70 rows of keeled scales and a ventral count of 230–314. Adults reach about 1,110 mm in total length with a 190 mm tail, and the underside fades to a whitish hue. Juveniles display olive or grey tones crossed by bold black transverse bands that are widest at the mid-body, a striking contrast to the adult’s muted palette. This species thrives along the coasts and islands of India and across a broad swath of the Arabian Sea, Persian Gulf, South and Southeast Asian seas, and even reaches the waters off the Seychelles, Madagascar, and the Andaman & Nicobar Islands. It is a true oceanic predator, diving to depths of 100 m and remaining submerged for up to five hours, thanks to specialized salt-excreting glands that keep its internal chemistry balanced. Its diet consists almost entirely of fish, which it subdues with a potent cocktail of neurotoxins and myotoxins, delivering an average venom yield of 7.9–9.0 mg per bite, enough to make even a 1.5 mg dose lethal to humans. One surprising trait is its dual activity pattern; unlike many sea snakes that favor night, H. schistosus is equally at home hunting in daylight and under the cover of darkness, a behavior that fuels its reputation among herpetologists as "cantankerous and savage," These aggressive tendencies are underscored by its epidemiological impact: more than half of all recorded sea-snake bites are attributed to this species, and it accounts for the majority of envenomings and fatalities, with an LD50 of 0.1125 mg/kg. Its venom’s potency, combined with a lethal human dose estimated at 1.5 mg, makes encounters with H. schistosus a serious medical concern in coastal communities. Yet, despite its notoriety, the snake remains a common sight among the twenty sea-snake species inhabiting Indian waters, where it continues to play a pivotal role in marine ecosystems as a top predator, influencing fish population dynamics and...

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