Should you ever be caught on the marshy plains of northwest Canada during springtime, mind your step. You’ll be in position to witness one of the world’s largest gatherings of snakes. But first they have to come slithering out of the ground. 

Red-sided garter snakes hibernate together in large groups. Hundreds of snakes may come together in an underground den. They share body heat and therefore stay warmer during winter. In the spring, when temperatures start to rise, writhing masses of red-sided garter snakes break free from their dens and migrate to their summer homes.

What guides them? Their sense of smell. The snakes’ long, forked tongues pick up scent molecules from the ground and air. The molecules are passed to a supersensitive taste receptor in each snake called a Jacobsen’s organ.

In collecting these smells, each snake creates a detailed scent map of its surroundings. That includes the familiar smell of its own den.

Scientists have tracked snakes
migrating up to 12 kilometers (about 7.5 miles) away from their dens. The snakes use their scent map to return to the same den year after year.