Snakes, often observed basking in the sun or slithering through vegetation, possess diverse behaviors. While many people associate them with above-ground environments, some snake species lead a hidden life beneath the surface. This subterranean existence allows them to access resources and protection. Indeed, many snake species burrow underground.
The Truth About Snakes Underground
Many snake species engage in burrowing, though it is not a universal characteristic. The term “fossorial” describes snakes specifically adapted for a subterranean lifestyle, spending a significant portion of their lives within burrows and tunnels. These truly fossorial species actively create their own underground passages, exhibiting physical features that aid in digging through soil.
This contrasts with other snakes that opportunistically use existing underground spaces, such as rodent burrows, tree root systems, or natural crevices, for shelter. While these snakes utilize subterranean environments, they do not possess specialized adaptations for active digging.
Why Snakes Seek Subterranean Havens
Snakes seek underground environments for several advantages, with thermoregulation being a key reason. As ectotherms, snakes rely on external heat sources to maintain their body temperature. Subterranean havens provide stable temperatures, protecting them from extreme heat on the surface during the day and preventing excessive cold during cooler periods or winter months. This allows them to avoid overheating or freezing, which is especially important for species in arid or temperate climates.
Burrowing also serves as a defense mechanism against predators. By retreating underground, snakes can effectively hide from a range of threats, including birds of prey and mammals. This concealment offers a secure refuge where they can avoid detection and minimize their vulnerability. The ability to quickly disappear into the soil provides an escape route.
For some species, the subterranean environment is ideal for ambushing prey. Sand boas, for instance, often bury themselves in loose soil or sand with only their heads exposed, waiting for unsuspecting small mammals, birds, or lizards to pass by. Once prey is within striking distance, they rapidly emerge to capture it, sometimes even dragging it further underground to constrict and consume it.
Underground spaces are also used for reproduction. Many snakes lay their eggs in burrows or concealed locations within the soil, which offers a stable and protected environment for incubation. This helps maintain consistent temperature and humidity levels, which are important for offspring development. Brumation, a state of dormancy similar to hibernation, is another reason snakes go underground, particularly in cooler climates. During brumation, snakes reduce their metabolic activity and seek shelter below the frost line to survive cold winter months, often congregating in communal dens called hibernacula.
Adaptations for a Subterranean Life
Snakes adapted to subterranean life exhibit physical features that facilitate their movement through soil. Many burrowing species possess pointed or shovel-shaped heads, often with a large rostral scale on the snout, which aids in pushing and displacing earth. This specialized head shape acts like a wedge, allowing them to navigate compact substrates.
Their eyes are typically small, sometimes reduced to tiny dark spots, or even covered by scales, reflecting their limited need for vision underground. This adaptation protects their eyes from abrasive soil particles. Instead, they rely on other senses, such as smell and vibrations, to navigate and locate prey.
Burrowing snakes commonly have smooth, cylindrical bodies, which reduce friction as they move through tight spaces. Their scales are often highly polished, which minimizes resistance and prevents dirt from adhering. Strong musculature along their bodies enables undulating movements to propel them through the soil. Some species also have specialized scales, such as keeled scales on their tails, that provide additional grip for pushing against the substrate.
Examples of Burrowing Snakes
Blind snakes (family Typhlopidae) are examples of truly fossorial snakes. They are small, worm-like reptiles with smooth, shiny scales and degenerate eyes covered by head scales. These snakes primarily feed on the eggs and larvae of ants and termites within their subterranean tunnels. The Brahminy blind snake (Ramphotyphlops braminus) is an all-female species that reproduces without fertilization and is often found in potted plants, contributing to its global distribution.
Worm snakes (Carphophis genus) are small, slender snakes native to eastern North America, often mistaken for earthworms. They possess small, pointed heads and smooth scales, which help them burrow through loose, moist soil and leaf litter. These snakes spend most of their time underground, feeding on insect larvae and earthworms.
Sand boas (Eryx genus) are non-venomous constrictors found in arid regions of Africa, the Middle East, and South Asia. These snakes are known for their burrowing habits, utilizing their stout, cylindrical bodies and wedge-shaped heads to “swim” through sand. Their eyes and nostrils are positioned on top of their heads, allowing them to remain hidden beneath the sand while watching for prey. The Kenyan sand boa (Eryx colubrinus) is a common example, often ambushing prey from its buried position.
Hognose snakes (Heterodon genus) are North American snakes characterized by their distinctive upturned, shovel-like snouts. This specialized rostral scale is used for digging in sandy or loose soils, allowing them to burrow with a sweeping, side-to-side motion. They dig to find prey, including toads, frogs, and reptile eggs. The Western hognose snake (Heterodon nasicus) is a common species that actively burrows for both shelter and hunting.