A Snake Got Into the House

A snake indoors is startling and almost never dangerous in most of North America. It came in through a gap, it is probably following mice, and it wants to leave.

First: contain, do not chase

Shut the doors of the room it is in. That turns an unknown problem into a known one, and it is the single most useful thing to do in the first minute.

Chasing a snake sends it under furniture, behind appliances or into a wall cavity, and a snake in a wall cavity is a far harder problem than a snake on a floor.

If you cannot contain it, note carefully where it went and what it looked like. That information is what makes the next step possible.

Then: give it an exit

Open an exterior door in that room, block the gap under the interior door with a towel, and leave it alone for a few hours.

Most snakes leave. They came in by accident, the room is exposed and unsuitable, and an open door at floor level is what they are looking for.

If it will not leave

A large plastic bin and something long to guide with — a broom, a rake handle — works for anything harmless. Place the bin on its side against a wall and steer the snake gently in, then tip it upright and carry it out.

Do not grab, do not use a shovel, and do not attempt any of this if you cannot identify the animal or the species is venomous where you live. In that case call animal control or a local removal service, and keep the room shut.

Where they get in

A snake needs a gap only slightly larger than its head, which for a garter or rat snake is well under two centimetres.

Why it came in

Almost always prey. A house with mice has an attractant, and a rat snake following a rodent trail into a crawlspace or a wall is doing what it is built to do.

That means the snake is a symptom. Sealing entry points helps, and dealing with the rodents removes the reason.

Closing the gaps

Steel wool packed into gaps around pipes and covered with expanding foam works, since snakes and rodents will not chew through it. Door sweeps on exterior doors. Repair damaged vent screening with metal mesh rather than plastic.

Do this in autumn if you can, before snakes look for overwintering sites, which is when a warm crawlspace becomes attractive for a different reason.

What not to do

Glue traps kill snakes slowly and catch anything else that passes. Snake repellents sold commercially have consistently failed testing. Mothballs are neither effective nor legal to use this way in many places, and they are a genuine hazard indoors.

Sealing and rodent control are the interventions that work, which is the same conclusion there's a snake in my yard reaches for outdoor encounters.

The basement and crawlspace case

Snakes found in basements are usually there because the basement is where the mice are, or because it offers a stable temperature. In autumn a warm crawlspace is exactly what a snake looks for to overwinter, which is why reports spike in September and October.

A snake that has settled in for winter will not leave voluntarily, and evicting it in December leaves it with nowhere to go. Sealing entry points in late summer, before that happens, is the version of this that works.