Double Equipment
Male snakes and lizards have two penises (hemipenes) but only use one at a time — and they often alternate sides between matings.
Male snakes and lizards possess hemipenes — a pair of penis-like organs stored inside the base of their tails. Despite having two, they only use one at a time during mating.
Each hemipenis is typically covered in spines, hooks, or ridges that help anchor it inside the female during copulation. The shape varies dramatically between species and is often used by scientists to identify different snake species.
Why two? There are several theories: - Having a "spare" allows more frequent mating (males often alternate sides) - The forked anatomy may have evolved alongside the female's paired reproductive tract - It may be an ancestral trait from a common ancestor
Snakes typically store their hemipenes inverted (inside-out) inside their bodies. During mating, one hemipenis everts (turns right-side-out) and engorges with blood. The process is similar to turning a sock inside-out.
Some female snakes can store sperm for months or even years after mating, using it to fertilize eggs long after any contact with males. A female has even given birth 5 years after her last contact with a male.