Garter snakes spend roughly half the year underground in communal dens, sometimes packing hundreds of snakes into a single site. These dens, called hibernacula, serve as winter shelters that the snakes return to year after year, often traveling long distances to reach the same spot. Whether you’ve stumbled across one in your yard or you’re curious about how these animals survive cold winters, here’s what to know.
What a Garter Snake Den Looks Like
Garter snake dens aren’t elaborate tunnels the snakes dig themselves. They’re existing gaps and cavities in the ground or in structures, places where snakes can get below the frost line and avoid freezing. Common den locations include spaces under large rocks, stone walls, old building foundations, front steps, and retaining walls made of railroad ties. In wilder settings, they use animal burrows, sinkholes in limestone, root systems of large trees, and crevices in rocky outcrops.
The entrance is often surprisingly small, just a crack or gap a few inches wide. What matters is that the cavity extends deep enough to stay above freezing all winter. In colder climates, that means the den needs to reach at least 14 inches below the surface, and natural dens often go much deeper. Inside, the space may branch into multiple chambers connected by narrow passages. Moisture matters too: the den needs to stay humid enough that the snakes don’t dehydrate during months of dormancy, but not so wet that they’re sitting in water.
Why They Den Together
Garter snakes are one of the most social snake species in North America, and their denning behavior is the clearest example. They hibernate in communities, with dozens to hundreds of snakes sharing a single den from roughly October through April. This isn’t random crowding. Good den sites that stay below the frost line, hold humidity, and resist flooding are limited in many landscapes, so snakes converge on the best available options. Packing together also provides a slight thermal benefit, as a mass of snakes loses heat more slowly than a single animal would.
Young snakes learn den locations by following chemical trails left by adults, which is one reason the same dens get used across generations. A well-established den may be decades old, with each new cohort of snakes picking up the scent trail and joining the group.
Spring Emergence and Mating Balls
When temperatures warm in spring, garter snakes emerge from their dens as a large group over the span of a few days to a couple of weeks. Males typically come out first, basking near the den entrance to raise their body temperature after months of dormancy. Females emerge shortly after, and mating begins almost immediately at the den site.
This is when you might see something startling: a writhing mass of snakes tangled together on the ground. This is a mating ball. When a female releases pheromones signaling she’s ready to mate, every nearby male responds. As many as a hundred males will coil around a single female, each trying to get into position. The male closest to her rubs his chin along her head, back, and sides while aligning his body with hers. Eventually one male succeeds, and the ball disperses. If you see a cluster of tangled garter snakes in early spring, you’re almost certainly looking at this mating behavior rather than anything aggressive.
The Narcisse Snake Dens
The most famous garter snake dens in the world are at Narcisse, Manitoba, about 80 miles north of Winnipeg. Four active dens there host tens of thousands of red-sided garter snakes, making it the largest known concentration of snakes on Earth. Every spring, the emergence draws visitors who can watch thousands of snakes streaming out of limestone sinkholes and mating on the surrounding ground. The site is maintained by the Manitoba government as a wildlife attraction, with self-guided trails and viewing platforms. Peak activity usually falls in late April to mid-May, depending on temperatures.
Finding a Den on Your Property
If you’ve noticed garter snakes congregating around your foundation, front steps, or a retaining wall in fall or early spring, you likely have a den. The most common residential den sites are gaps in stone foundations, spaces beneath concrete porches, and cavities under stacked landscape materials like railroad ties or rock walls. You might see a handful of snakes or several dozen, depending on the site.
Before you decide what to do, it’s worth knowing what these snakes contribute. Garter snakes are effective pest control. They eat mice, slugs, and insects that damage gardens and structures. In areas with high mouse populations, garter snakes help reduce the risk of rodent-borne diseases like hantavirus, all without pesticides or traps. Many states, including Minnesota, classify garter snakes as a protected species, and killing or collecting them is illegal.
Moving a Den Away From Your Home
If the den location is genuinely problematic, you have options that don’t involve harming the snakes. The most effective approach combines two steps: making the current site unappealing and creating a better alternative elsewhere on your property.
To discourage snakes from the area around your foundation or steps, remove all nearby cover. That means clearing away rock piles, brush, railroad ties, tall weeds, and anything else that provides hiding spots. If the area around the den entrance is bare dirt with no shelter, the snakes will have much less reason to stay. You can also install a one-way door over the entry point, a simple mesh device that lets snakes exit but blocks them from re-entering. This is legal on your own property in most states without a permit.
To give them somewhere better to go, set up habitat in a different part of your yard. Build a rock pile or brush pile in a sunny spot, ideally at least 50 feet from your house. If you want the snakes to use it as a year-round den and not just a summer hiding spot, dig a hole about 14 inches deep before stacking the rocks on top. That depth gets below the frost line in milder climates and gives the snakes a viable overwintering site. Within a season or two, the snakes will typically relocate to the new habitat on their own.
Relocating snakes off your property entirely is a different matter. In many states, moving wildlife to a new location requires a permit from your state fish and wildlife agency. Oregon, for example, requires a permit from the Oregon Department of Fish and Wildlife for any snake relocation off-property. Check your local regulations before attempting this, as the rules vary significantly by state.