Snakes, with their unique forms, possess small, claw-like structures known as spurs. These intriguing features offer a glimpse into their evolutionary journey and serve specific roles for the species that retain them.
What Are Snake Spurs?
Snake spurs are small, external protrusions found on either side of a snake’s cloaca, which is the single opening for waste and reproduction. They are composed of keratin, like human fingernails, and often contain a bony core, which is a remnant of a femur bone.
These spurs are considered vestigial structures, meaning they are remnants of organs or limbs that were functional in ancestral species but have lost most of their original purpose. Despite their reduced function, they are connected to muscles, nerves, and blood vessels, allowing for independent movement.
Why Do Snakes Have Spurs?
Spurs are an echo of the snake’s evolutionary past, remnants of hind limbs from their ancient, legged ancestors. Fossil records, such as Najash rionegrina, show early snakes possessed sacrums, pelvic girdles, and robust hind limbs. Over millions of years, as snakes adapted to new environments, their limbs became less necessary, leading to gradual reduction.
While no longer used for locomotion, these spurs retain important functions, particularly in courtship and mating. Male snakes commonly use their spurs to stimulate and clasp the female during copulation. This “tickling” action helps position the female and increases her receptiveness. In some species, male snakes also employ their spurs during competitive interactions with other males for mating opportunities.
Which Snakes Possess Spurs?
The presence of spurs is not universal across all snake species; they are primarily found in more ancient lineages. The most prominent examples are snakes belonging to the Boidae family (boas) and the Pythonidae family (pythons). These groups are considered basal clades, representing earlier diverging branches in the snake evolutionary tree.
While spurs are characteristic of boas and pythons, their size and visibility can vary significantly, even within these families. Male snakes generally have more developed and noticeable spurs than females. Some other snake species may possess very small, almost imperceptible spurs, or none at all, particularly in more recently evolved families like Colubridae.
Are Spurs Harmful or Dangerous?
Snake spurs are generally harmless to humans. They are not venomous and do not contain any toxins. These small structures are not used for biting or inflicting serious injury as a defense mechanism.
Concerns about their potential to cause harm are unfounded. Spurs are small and, if broken, usually regrow without serious complications, similar to a fingernail. Their primary roles relate to mating and are a testament to the snake’s evolutionary history, not a threat.