On the marshy plains of northwest Canada, it’s springtime. Watch your step and witness one of the world’s largest gatherings of snakes. Snakes come slithering out of the ground.

Red-sided garter snakes hibernate together in large groups. This allows them to stay warmer. In the spring, when temperatures start to rise, masses of red-garter snakes break free from their dens. Then they migrate to their summer homes.

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

Each snake creates a scent map of its surroundings, including the smell of its own den. Scientists have tracked snakes migrating up to 12 kilometers (about 7.5 miles) from their dens. The snakes will use their scent map to return to the same den before the next winter.