Yellow Sac Spider

Learn about Utah Yellow Sac Spiders

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Yellow sac spiders are relatively small, with a body length of approximately 1/4 inch for both males and females. The Yellow Sac spider’s body is generally pale beige or yellow in coloring. The body is divided into two sections: the abdomen and the cephalothorax. Yellow sac spiders are nocturnal and usually retreat to a sac-like web woven in corners or under objects such as furniture during the day.


Yellow sac spiders prefer hiding in dark crevices during the day and hunting a night. They may build their sacs on tree trunks or houses next to walls, under siding, or corners. Indoors they prefer to construct webs in dark corners of homes and garages where they won’t be disturbed. The Yellow Sac spider will hang out motionless under their silk shelter, waiting for potential prey to approach. While people often find yellow sac spiders in light fixtures and windowsills, they are frequently seen crawling around walls or ceilings inside homes. They may even hide in rolled-up towels or clothing left on the floor.

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The yellow sac spider hunts for its prey at night and relies on speed to capture its victims. While it prefers to hunt for its food, the yellow sac spider can also make do with eating leftovers. The yellow sac spider is an opportunistic hunter of insects and other spiders. It usually preys on flies, beetles, and caterpillars. It also feeds on garden pests, insects, and their eggs. The spider has been known to eat its kind and other yellow sac spiders. The species also feeds on crickets, firebrats, and mites. The yellow sac spider usually eats the insects near it, but it can travel over 100 feet away to find food if needed.

Yellow Sac Spider Life Cycle & Reproduction

The mating behavior of spiders is often complex, particularly in species with elaborate courtship rituals. In some species, males present a gift (usually food) to females during courtship. In some species, a male will only approach a female in her web, and he must first remove the web or otherwise disable it before mating. Male spiders identify themselves as females by the patterns of tapping on the web or vibrations that they produce. The female yellow sac spider can lay up to five egg sacs, each with as many as 40 eggs. She makes the first egg sac within a few days of mating and can have more than 500 eggs per year. The eggs hatch between 4 and 17 days, depending on the conditions and year. The young spiders remain in the sac until they molt for the first time, which can occur within three days of hatching. They then disperse and start to hunt for prey. The yellow sac spider may live for up to two years.

Yellow Sac Spider Threat

Yellow Sac spiders can bite humans but are not considered dangerous to people or pets unless there is an allergic reaction to their venom. The bites of yellow sac spider may leave lesions similar to a brown recluse spider bite. However, contrary to popular belief, yellow sac spider bites do not cause necrosis (dead tissue) around the bite area. Yellow Sac spiders are most active at night, but they will bite when disturbed during the day.

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