Yellow sac spiders, also called agrarian sac spiders or black-footed yellow sac spiders, are widespread spiders that are commonly found inside homes. These aggressive spiders are known for their painful bites and are unwelcome pests. Here are three things you need to know about yellow sac spiders.

How can they be identified?

These spiders are easy to identify, even if you're not a spider expert. As their name suggests, they are either light yellow or cream-colored. Their bodies can reach sizes of up to 10 millimeters, not including their legs. Their tarsi—the end segment of their legs—are dark brown and stand in stark contrast to their pale bodies. This gives the effect that they're wearing tiny, brown shoes; this can help you distinguish them from other pale spiders you see around your house.

Why are they pests?

Yellow sac spiders are pests for two reasons: they can thrive indoors and they have a painful bite. While other outdoor spiders may not last long indoors, yellow sac spiders are adaptable and are able to establish themselves inside homes as long as there is enough food (bugs and other spiders) for them to eat.

Their bites are also a concern. These spiders are nocturnal and roam your house at night looking for food. If you brush up against one during the night—like while you're sleeping—the spider may bite you. This bite causes stinging pain, and in some cases, blisters. Some people develop sores or ulcers at the site of the bite which can take weeks to heal.

How are they controlled?

The easiest way to control yellow sac spiders is to keep them outside. Spiders can get through a gap that is only 1/16 inch tall, so you need to get rid of any gaps that are this size or larger. Prime locations for spider entry are the gaps beneath your exterior doors, the gaps around utility entries and tears in your window screens. Weather stripping can be used underneath your doors, while caulk can be used around the entry points of outdoor faucets, cable wires and other utility entries. Torn window screens can be patched or replaced.

If yellow sac spiders have already infested your house, you'll also need to use insecticides. These insecticides should be sprayed in areas where the spiders hide, like in dark corners and beneath furniture. The outside of your house should also be sprayed to keep more spiders from coming inside.

Yellow sac spiders can take over your house if they're able to get inside, so make sure that they stay outdoors where they belong. If they infest your home, call a pest removal company like Select Pest Control to help you get rid of them.