Red-sided garter snakes have a strange mating ritual. As they emerge from hibernation in spring, thousands of male snakes will desperately rush the females in an epic battle to reproduce.

The snakes form “mating balls,” in which one female can find herself outnumbered by dozens of frantically-writhing males. With up to 10,000 snakes living in a single den, the sight is mind-blowing as snakes literally carpet the ground.

Female snakes release pheromones from their skin as they slither along the ground, luring males who track her scent using an organ in their mouths. They court her by flicking their tongues and rubbing their chins along her body as she tries to escape.

Eventually, the lucky guy who manages to get closest will insert his sperm into the female, sometimes leaving behind a plug that stops others from mating with her. When the plug dissolves in a few days, the female can actually look for another mate. Or she can store the sperm until she is ready to give birth to up to 100 babies.

Although females are several times larger than males, the sheer number of suitors can be overwhelming — and sometimes dangerous. Male snakes can sometimes cut off a female’s oxygen supply while attempting to mate!

Garter snakes are actually quite harmless to humans, though. Those who want to see the fascinating phenomenon up close can visit Narcisse Snake Dens in Manitoba, Canada, which is home to the world’s largest gathering of snakes.