Yellow Sac Spiders

Appearance / Identification

Yellow Sac Spider Illustration
Yellow Sac Spider

Measuring 10 mm in body length, yellow sac spiders are relatively small. As their name implies, these arachnids are pale yellow in color, although green, tan, straw and light-brown specimens also exist. Upon close inspection, yellow sac spiders have dark mouthparts, as well as a band running laterally down the abdomen. The front legs of the yellow sac spider are longer than the other three pairs. Yellow sac spiders are often confused with other species and are easy to overlook.

In the daytime, yellow sac spiders are found inside their flattened silk tubes. In warm seasons, these spiders tend to reside in gardens, leaf piles, woodpiles and timber. In fall, they migrate indoors and can be seen crawling up and down walls, as well as across ceilings and vertical surfaces. Yellow sac spider populations increase significantly in fall, leading to indoor infestations.

Yellow sac spiders hunt for prey at night. These arachnids move swiftly, wielding their front legs before them. They consume small insects and arthropods, as well as other spiders. Some yellow sac spiders have been known to feed on spiders much larger than themselves and others consume their own eggs.

Yellow sac spiders typically are not aggressive to humans and would be unlikely to bite. However, they might become defensive and bite when they feel trapped or threatened such as being crushed. Their venom is not medically threatening to the average adult. If there are medical concerns, the person should speak to a medical professional.