Spider identification
The flat little spider that shoots sideways across the siding when you reach for the door, then freezes against the trim, is a running crab spider. There are several species and they all live the same way: fast, flat, out in the sun, and never in a web.
Flat bodied, 5 to 8 mm, grey brown, tan or mottled to match bark and siding, with the legs held out to the sides like a crab and the second pair longest. It runs sideways and backwards as readily as forwards, which is the tell. No web. It shelters under siding laps, trim, bark and shutters and spins a small flat silk cell to lay eggs in.
Sunny siding, fence boards, window and door frames, tree trunks, patio furniture and deck rails. It hunts by sight on open surfaces and slips into cracks when disturbed, including the window track, which is how it ends up on the inside of the glass.
Active from spring to fall on warm days, most noticeable in May and June and again in September. Some species overwinter as adults under bark and trim and are among the first spiders moving in spring.
Not a concern. It is small, fast and flees; a bite is not something to expect. Most "spider bites" in Ontario are never confirmed; see the bite section of our guide to common spiders in Ontario for what a real one looks like.
Running crab spiders are not a reason for a visit and we do not treat for them. They leave no webs or mess and they eat small insects on the siding. If one is on the inside of a window it came through the track; a brush of weatherstripping in the track is the fix. The spiders we treat are the ones building webs on the eaves, lights and corners. Every visit ends with a written summary of what we found and where product was applied, if any. Our spider control service and 60 day guarantee pages have the details and pricing.
Zebra jumper, Wolf spider, Flower crab spider. The zebra jumper is black and white and hops. Young wolf spiders are hairier, rounder and run forwards on the ground rather than sideways on walls. Flower crab spiders are the same shape but rounder, often white or yellow, and sit in flowers rather than on the house. The full list with photos is in the common spiders in Ontario guide.
Good to know
Almost always a running crab spider. It is harmless and lives on the sunny side of the house hunting small insects.
Through the window track or a gap in the weatherstripping. Running crab spiders are flat enough to use gaps a few millimetres wide.
It is not something to expect. They are small, timid and run at the first movement.
Related guides: Keeping spiders away from windows, eaves and lights, Do you need to spray for spiders. Service areas where this spider is found: Sarnia and Bright's Grove, Bayfield.
