The elongated, limbless body of a snake is a familiar sight, but not every slithering reptile belongs to the suborder Serpentes. The term “legless lizard” describes a variety of reptiles that have independently evolved a snake-like body plan, which is a key reason for the common confusion. These animals are true lizards, classified within the suborder Lacertilia, and their appearance is a remarkable example of convergent evolution.
What Defines a Legless Lizard
The absence of limbs in these reptiles is a morphological feature that has arisen multiple times across the evolutionary history of lizards. This evolutionary trait, known as limblessness, has developed in at least 25 different lineages within the order Squamata, often driven by ecological pressures like a burrowing or fossorial lifestyle. Lizards that inhabit dense vegetation or loose soil benefit from a streamlined body that allows for more efficient movement through their environment.
Despite the loss of external appendages, legless lizards retain internal and skeletal characteristics that confirm their status as lizards. Many species still possess vestigial remnants of the pectoral and pelvic girdles, the skeletal structures that support the limbs. Even when external limbs are completely absent, elements like the ilium, a part of the pelvic bone, are often retained internally. These hidden skeletal features distinguish them from snakes, whose evolutionary trajectory involved a more complete loss of these structures.
How to Distinguish Them From True Snakes
The most reliable way to differentiate a legless lizard from a snake involves observing specific external anatomical features retained from their lizard ancestry. A primary distinction is the presence of movable eyelids in most legless lizards, allowing them to blink and close their eyes. Snakes lack true eyelids; their eyes are covered by a fused, transparent scale called a spectacle, meaning they cannot blink.
Another easily observable difference is the presence of external ear openings, visible as small holes or depressions on the sides of the head. Snakes have no such external openings and instead perceive ground vibrations through their jawbones. Furthermore, the scales on the underside of a legless lizard are typically small and uniform, resembling the scales on the rest of its body.
True snakes possess a single row of large, specialized, rectangular ventral scutes that span the entire width of their belly and are used for locomotion. The tail structure also provides a clear difference, as a legless lizard’s tail is generally much longer than a snake’s, often accounting for up to two-thirds of its total body length. Many legless lizards also exhibit autotomy, the ability to voluntarily shed their tail as a defense mechanism, a trait not shared by snakes.
Major Groups and Ecological Roles
The diversity of legless lizards is reflected in the various families that have evolved this body form, including the Anguidae, known as Glass Lizards or slowworms, and the Pygopodidae, or Flap-footed Lizards. The Glass Lizards, such as those in the genus Ophisaurus, are found across North America, Europe, and Asia. Pygopodids are endemic to Australia and New Guinea and are unique in that they are close relatives of geckos.
Another group, the Dibamidae, or Blind Lizards, are highly specialized burrowers inhabiting Southeast Asia and Mexico. These reptiles are primarily fossorial, spending the majority of their lives underground. Their diet generally consists of small, soft-bodied invertebrates, such as insect larvae, spiders, slugs, and snails, which they forage for in their sheltered habitats. Because of their shy, hidden nature and their preference for small prey, nearly all species of legless lizards are considered harmless to humans.