Mind-Blowing! Male Snakes and Lizards Have TWO Penises!

Male snakes and lizards, collectively known as squamates, possess a fascinating reproductive adaptation: a pair of intromittent organs called hemipenes. These structures are typically stored inverted within the base of the tail and are everted for reproduction, usually with only one being deployed during mating. Unlike the single genital tubercle found in most other amniotes like mammals, crocodilians, and turtles, squamate hemipenes arise from a different embryonic origin, developing from the same cells that would otherwise form limbs.

These paired organs exhibit remarkable diversity in their morphology across species, ranging from bilobed to cylindrical shapes and often adorned with an array of spines, hooks, or ridges. This elaborate ornamentation is not merely for show; it is thought to play a crucial role in mating, helping to anchor the male to the female during copulation and potentially ensuring longer, more successful sperm transfer. Sperm is transported along an external groove on the hemipenis called the sulcus spermaticus, a structural difference from the internal sperm transport seen in mammalian penises.

The evolutionary advantage of having two hemipenes is a subject of ongoing scientific inquiry. One hypothesis suggests that having a second hemipenis acts as a "backup," ensuring mating can proceed even if one side is depleted of sperm. Furthermore, the rapid evolution of hemipenial morphology, which can change six times faster than other body parts, suggests their importance in reproductive isolation and speciation. Their unique and varied forms are so distinct that they are often used by taxonomists to differentiate between closely related species. After mating, specialized retractor muscles pull the hemipenis back into its inverted position within the body.