Yellow Sac Spiders


Cheiracanthium inclusum & Cheiracanthium mildei

Appearance / Identification

Yellow Sac Spider Illustration
Yellow Sac Spider

The yellow sac spider (Cheiracanthium inclusum) is a small spider with a body length of about ¼ inch for both males and females. It has a pale beige to yellow color and is often has a tinge of green. Its chelicerae (fangs), and the tips of their legs are dark brown. This leg coloration gives these spiders the appearance of having dark colored feet. The top part of its abdomen includes a dark, lance-shaped mark that runs down the middle of the abdomen from the point where the thorax and abdomen meet to about the mid-point of the abdomen. Another species of yellow sac spider found in the United States, Cheiracanthium mildei, looks very much like C. inclusum.


Yellow sac spiders usually feed on other spiders, plus agricultural and garden pest insects and their eggs. However, if food sources are limited these spiders become cannibalistic and may consume their own eggs. Their preferred habitats around the home are in trees, gardens, leaf piles, woodpiles and bushes. While yellow sac spiders are usually most active at night and during the day will retreat to their web masses (sacs) for protection against predators. Outdoors, these spiders normally are found hiding in rolled up leaves or in other debris in small, hidden locations. In addition to protection, these daytime hiding places also function as molting sites (shedding of their outer “skin” in order to grow larger), mating, egg laying, and hibernating sites.

As the weather begins to cool during the fall months and with the yellow sac spider population increasing, they are apt to move inside homes and thus lead to an interior infestation. Indoors their protective sacs sometimes are seen in the corners of rooms or where the ceiling and walls meet. C. mildei is commonly found in man-made structures, while C. inclusum is likely to be seen outdoors. In general, the female C. mildei lays her eggs almost exclusively indoors.


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.


Male yellow sac spiders will hunt for females and breed with them in the early summer. Females typically mate only once but produce as many as five egg sacs, each of which contains approximately 40 eggs. Their egg sac serves to protect not only the mature spiders, but also to protect the eggs and immature stages of the yellow sac spider.


The appearance of either immature or mature spiders and their protective sacs are signs of a yellow sac spider problem.


Yellow sac spiders are found throughout most all of the United States, but are fewer in number within the northern, colder climates.



Yellow sac spiders are nighttime hunters that search for prey rather than catching their prey within a web. Therefore, these spiders may come into contact with people if they should be trapped between a person ‘s skin and bed sheets, clothing or shoes and if a person provokes a spider to bite while gardening or working in a location of preferred yellow sac spider habitat.

Yellow sac spider bites are relatively painless, but do cause bite symptoms that include lots of pain at first and the subsequent develop of other symptoms such as redness of the skin, swelling and itchiness. Some bites may cause systemic reactions with fever, malaise, muscle cramps, and nausea. A necrotic lesion and ulceration may also occur at the site of the bite, but this condition is extremely rare. In general, yellow sac spider bites may be initially painful but rarely result in any serious medical conditions.

Medical articles frequently report that spiders from the yellow sac genus Cheiracanthium cause necrosis. However, in a study that looked at 20 cases of confirmed and verified bites by Cheiracanthium spiders from the United States and Australia, no bites developed necrosis. Reports that Cheiracanthium cause necrosis seem to be based on venom experiments on rabbits and guinea pigs, incidental spider bites, and indefinite reports in medical literature.


Yellow sac spider prevention is best accomplished by sealing holes, cracks and gaps in the home ‘s doors, windows and foundation that enable the spiders to enter the home. In addition, removing inside clutter that serves as harborage for spiders is also helpful. Should the homeowner need assistance to control yellow sac spiders or any other spiders, contact your pest management professional (PMP) and request an inspection. Your PMP will use his inspection findings to prepare a comprehensive pest management plan that will effectively and efficiently deal with the specific pest problem. Your PMP inspection includes looking for egg sacs in the upper corners of rooms, spaces behind pictures, ceilings, window moldings, and curtains and blinds. His recommendations will also include using a vacuum to remove sacs and removing and discarding vacuum cleaner bags to prevent reinfestations.