The Yellow Sac Spider Surprisingly Doesn't Build a Web

The American yellow sac spider (Cheiracanthium inclusum) is a common species in North America Ali Majdfar / Getty Images

The yellow sac spider is one of the most common spiders humans encounter, as they're often wandering indoors or hanging out in gardens. Scientists also believe they account for more human insect bites than any other spider.

These spiders are known for their pale yellow color and small size, making them hard to spot until they build their distinctive silk sacs that they build in lieu of webs. These spiders are fast movers and often found hiding in leaf litter or human-made structures.

The American yellow sac spider (Cheiracanthium inclusum) is a common species in North America, while Cheiracanthium mildei, an introduced species, is often found in urban areas. Yellow sac spiders play a vital role in ecosystems, but that doesn't make them entirely harmless; they're likely to bite if provoked. Luckily, these bites are rarely serious.

How to Identify the Yellow Sac Spider

The yellow sac spider is a small species with a body length of about 0.2 to 0.4 inches (5 to 10 millimeters). It is easily identified by its light yellow or cream-colored body, often with a slightly darker dorsal stripe running along its abdomen. They have eight eyes, arranged in two horizontal rows.

Yellow sac spiders are sometimes confused with brown recluse spiders, but they lack the recluse's distinctive violin-shaped marking. Instead, yellow sac spiders have dark brown markings on the tips of their legs and jaws.

Are Yellow Sac Spiders Dangerous?

Yellow sac spider bites can result in redness, swelling and a burning sensation on the human skin surface, but they are generally mild. Most bites occur when a spider feels trapped, such as when one is accidentally squished against the skin.

While these spiders rarely bite, they are known to readily bite if provoked. Their venom is not medically significant for most people, and symptoms usually subside within a few days without treatment.

For peace of mind, it's always best to consult a medical professional if you experience an allergic reaction or lingering symptoms.

Where Are Yellow Sac Spiders Commonly Found?

Yellow sac spiders are highly adaptable and can be found in a variety of environments, including gardens, forests and human-made structures.

Spiders hide during the day in small silk sacs, often constructed in corners, behind furniture or along ceilings. In outdoor environments, these sacs can be found under leaves, bark or rocks.

These spiders are widespread across North and South America, Europe and parts of Asia. They prefer warm, dry habitats and are especially active at night, when they hunt for prey.

What Attracts and Deters Yellow Sac Spiders?

Yellow sac spiders are attracted to areas with abundant prey and sheltered hiding spots.

They catch airborne prey, like small insects, so homes with lots of flies or moths may inadvertently invite these spiders indoors. Leaf litter, cluttered spaces and gaps in walls or windows also provide ideal habitats for these arachnids.

To deter yellow sac spiders, keep your home clean and free of clutter. Seal cracks and gaps around windows and doors, and regularly remove spider webs and egg sacs.

Spiders deposit their egg masses in hidden areas, and since egg laying generally occurs in the spring, inspecting corners and ceilings during this time can help prevent infestations.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.