Sea snakes are a diverse group of marine reptiles that have adapted to life in the ocean. The question of whether these snakes visit land has a nuanced answer. While some sea snake species are almost entirely aquatic and rarely, if ever, come ashore, others regularly venture onto land for various purposes.
Different Types of Sea Snakes and Their Land Habits
Sea snakes are broadly categorized into two main groups based on their terrestrial habits: “true sea snakes” (subfamily Hydrophiinae) and “sea kraits” (subfamily Laticaudinae). True sea snakes, comprising about 64 species, spend the majority of their lives in the ocean, even giving birth to live young in the water. These species are highly adapted to marine life and typically cannot move effectively on land. For instance, the yellow-bellied sea snake is found in tropical waters and is an aquatic species; individuals can sometimes wash ashore.
In contrast, sea kraits, including eight species, are semi-aquatic and regularly return to land. They exhibit traits intermediate between fully aquatic sea snakes and land-dwelling snakes. A key distinction lies in their ventral scales: true sea snakes have reduced or absent ventral scales, broad scales on a snake’s belly that aid in gripping surfaces for movement. Sea kraits, however, have retained these wider ventral scales, similar to their terrestrial ancestors, allowing them to move efficiently on land. This anatomical difference explains their varying degrees of terrestrial mobility.
Reasons Sea Snakes Visit Land
For sea krait species, terrestrial excursions are a regular part of their life cycle. One primary reason is reproduction; sea kraits are oviparous, meaning they lay eggs on land. Females typically deposit clutches of eggs in rock crevices or under sand above the high-tide line.
Sea kraits also come ashore to shed their skin. On land, they rub against rough surfaces like rocks to slough off old skin, a process more challenging in water. Land is also used for rest and thermoregulation. They bask in the sun to warm their bodies or seek shelter in cooler microclimates, like rock crevices, to avoid extreme temperatures. Access to freshwater is another reason for terrestrial visits, as some species seek freshwater pools or sources like rainwater or estuaries to drink and maintain water balance.
Adaptations for Water and Land Movement
Sea snakes possess physical adaptations that enable their aquatic lifestyle, yet these same features can limit their terrestrial movement. Most sea snakes have laterally flattened, paddle-like tails, effective for propulsion and swimming. Their bodies are often laterally compressed, giving them an eel-like appearance aiding aquatic efficiency. Many species absorb oxygen through their skin, allowing for prolonged underwater dives, and they have specialized salt glands, under the tongue, to excrete excess salt from their marine environment.
Adaptations for an entirely aquatic life come with trade-offs for land movement. True sea snakes, with their reduced or absent ventral scales, are largely helpless, barely crawling on land, making them vulnerable if stranded ashore. In contrast, sea kraits retain prominent ventral scales, providing the necessary grip for terrestrial locomotion. While their paddle-like tails are efficient for swimming, they can still move on land, albeit slower than their aquatic speed. This combination of aquatic and terrestrial features allows sea kraits to navigate both environments for their specialized needs.