Yellow Sac Spiders: What to Know

Medically Reviewed by Dany Paul Baby, MD on January 17, 2023
5 min read

The colorful yellow sac spider is a harmful pest found throughout America. This spider only grows to the size of a nickel, but it delivers a painful bite that can cause necrotic lesions and other symptoms. These pests often invade houses and other human-made structures. Here’s what you need to know about yellow sac spider identification, health risks, treatment, and prevention. 

The yellow sac spider belongs to the family Clubionidae, a group of sac spiders. These nocturnal spiders get their name from the small sacs that they hide in during the day. The yellow sac spider can make a new cocoon in 10 to 15 minutes and typically hangs this sac in the corner of rooms or trees. 

What do yellow sac spiders look like? The yellow sac spider’s appearance differs slightly by species. Cheiracanthium inclusum has a light yellow or cream body, while Cheiracanthium mildei has a greenish abdomen and a yellow head and thorax. 

Both species have brown jaws, darker legs, and dark dorsal stripes running vertically across the abdomen. They have eight eyes in two horizontal rows. 

Female yellow sac spiders typically range from 5 to 10 millimeters long, while males are 4 to 8 millimeters. The males have darker and more slender bodies. 

The yellow sac spider has developed scopulae on its feet. These dense hairs help the spider climb and hunt for prey in grasses, trees, and other vegetation. 

What do yellow sac spiders eat? This spider is an insectivore that preys on other spiders and non-insect arthropods like cotton plant bugs, fruit flies, fleahoppers, and leafhoppers. It also eats nectar as it forages. 

The yellow sac spider’s diet may affect its color. Researchers have observed that the spider has a redder color after eating red-eyed fruit flies and a green hue after eating bright-green lepidopteran caterpillars. 

Unlike many spiders, the yellow sac spider doesn’t passively capture prey in a spiderweb. These species actively hunt their prey at night, bringing them into close contact with humans. 

Do yellow sac spiders jump? Yellow sac spiders don’t jump. They move by climbing and scurrying quickly across ceilings, walls, and vegetation. If startled, they may drop a silk line to flee. 

What is the yellow sac spider lifecycle? The female yellow sac spider lays eggs around 14 days after mating. The female places the eggs in a silken cocoon and guards them until they hatch. C. inclusum usually deposits its cocoons outdoors under leaves or plants, while C. mildei prefers to lay eggs inside human-made structures. 

Once the eggs hatch, the young spiderlings hide in the cocoon during daylight and venture out at night to hunt for prey. They leave the cocoon after around 17 days, and the female spider can lay more eggs. One female spider can produce one to five generations, but the average spider only lays two egg masses. 

Male yellow sac spiders mature at 119 days, while females mature at 134 days. Environmental factors like humidity and temperature can affect maturity rates.

There are two species of yellow sac spiders in America:  

C. inclusum. This spider is native to most regions in the United States, except for some northern states. People often encounter this species while doing yard work in warm weather. 

C. mildei. This species comes from Europe and was likely introduced during the 1940s. It’s more likely to be found inside than C. inclusum

A third species, Cheiracanthium punctorium, lives in central Europe. The spiderlings can travel long distances using silk lines as balloons. Like the other two species, C. punctorium grows in the spring, reproduces in the summer, and dies in the winter.

C. inclusum lives in most areas of the United States. C. mildei was first discovered in northeastern states, but experts speculate that this species’ range has expanded in the last few decades. 

C. punctorium has spread across central Europe since the mid-20th century. You can find this species in the Baltic states, north Germany, and south Sweden.

You may spot this distinctive yellow spider in several locations inside and around your home, including: 

  • Ceilings
  • Corners of walls
  • On the ground on or under foliage, leaf litter, and stones 
  • On house siding 
  • Under windowsills

These pests also create small sacs or cocoons to hide in during the daytime. You may find the sacs on your ceilings and walls or hidden behind shelves and picture frames.

Spider-friendly hiding places can attract yellow sac spiders to your house or yard. For example, you may get these pests if you have: 

  • Clutter 
  • Cracks in your house’s foundation 
  • Storage areas like attics and basements 
  • Vegetation close to the foundation 
  • Wood piles near the house

Other insects can also draw in hungry yellow sac spiders looking for prey.

Do yellow sac spiders bite? All species of this spider can bite humans and pets. C. mildei is the most aggressive species and will bite humans without reason. People often get bitten when they encounter C. inclusum while gardening or when a spider gets into their clothing, sheets, or shoes. 

Are yellow sac spiders dangerous? The yellow sac spider has a painful bite that may contain harmful venom. Symptoms of a yellow sac spider bite include: 

  • Painful stinging feeling when bitten
  • Mild swelling
  • Redness 
  • Skin lesions

Most yellow sac spider bites don’t cause serious side effects. You can typically treat a bite at home with these steps: 

  • Washing the bite with warm water and soap.
  • Applying ice for 15 minutes on and off as needed 
  • Taking an anti-inflammatory pain medicine to reduce inflammation

You can also soothe a painful spider bite with aloe or peppermint oil.

You can use a few simple methods to eliminate yellow sac spiders, such as: 

  • Applying spider pesticides around doors and windows, foundations, and eaves
  • Finding and destroying egg sacs before they hatch
  • Using a hose to rinse spiders off your house’s exterior 
  • Vacuuming up spiders

These tips can help keep you safe from the yellow sac spider and its painful bite.