Yellow Sac Spider, Black-footed Yellow Sac Spider
Cheiracanthium inclusum
Miturgidae (Prowling Spiders), Order Araneae
Physical Description
The body is oval-shaped with a pear-shaped, slightly tapered abdomen and a robust, yellowish cephalothorax. The surface is smooth and sparsely covered with fine hairs, lacking striking patterns.
Size Estimate
Body length typically ranges from 5 to 10 millimeters, with a leg span around 20 to 25 millimeters, representing a typical adult or sub-adult specimen.
Coloration & Markings
Pale yellow, yellowish-green, or beige overall, sometimes featuring a slightly darker dorsal stripe running down the center of the abdomen. The tips of the chelicerae and feet may appear slightly darker.
Web Type
Does not build an orb or sheet web. Instead, it constructs a silken tubular retreat or sac, usually in corners, under peeling paint, or along door and window frames, where it rests during the day.
Eye Arrangement
Eight eyes arranged in two relatively uniform, slightly recurved rows of four eyes each, which is characteristic of the family Miturgidae.
Leg Characteristics
Long, forward-facing legs with the first pair noticeably longer than the others, featuring distinct dark claws at the tips and fine spines. They often rest with all four pairs of legs spread outward against a flat surface.
Venom & Safety Information
Venom Information
Contains a cytolytic venom used to immobilize prey. The bite can be painful, causing localized burning, redness, and swelling, but it is generally not life-threatening to humans.
Medical Significance
Mildly medically significant due to the potential for painful necrotic-like lesions historically attributed to their bites, though recent studies suggest true tissue necrosis is rare. Symptoms typically resolve on their own within a few days.
Safety Recommendations
Avoid direct handling, shake out clothing and bedding if left undisturbed for long periods, and gently relocate individuals outdoors using a cup and piece of paper.
Habitat & Behavior
Habitat & Range
Found throughout the Americas, commonly inhabiting foliage, tall grasses, gardens, and frequently venturing indoors into homes, garages, and around door frames.
Behavior & Temperament
Active nocturnal hunters that leave their silken sacs at night to forage. They are generally defensive if cornered or trapped against the skin and are known to bite more readily than many other common household spiders.
Diet & Prey
Carnivorous, feeding on a wide variety of small insects including flies, aphids, moths, and other spiders, using active stalking and swift grasping rather than webs.
Seasonal Activity
Most active during the warm spring, summer, and early autumn months, with encounters peaking indoors as temperatures drop and they seek shelter.
Description
The Yellow Sac Spider is a common, pale-colored hunter often encountered around human habitations. Known for its nocturnal prowling and distinctive daytime silken retreats tucked into corners and door frames, it plays an active role in keeping indoor and outdoor insect populations in check.
Key Features
Pale yellow to yellowish-green coloration, noticeably elongated first pair of legs, lack of prominent abdominal markings, and the habit of resting inside a small silken sac.
Similar Species
Other sac spiders such as Cheiracanthium mildei, which is slightly larger and often found indoors in temperate regions, distinguishable primarily through microscopic examination of genital structures.
Life Cycle
Females construct silken egg sacs in late spring or summer, laying several dozen eggs. Spiderlings emerge and mature over the course of a year, overwintering in protected silk retreats.
Ecological Importance
Serves as an effective natural pest control agent by actively hunting and consuming numerous agricultural and household insect pests.
Conservation Status
Not evaluated by the IUCN, but populations are abundant, widespread, and secure globally.
Interesting Facts
Yellow sac spiders are among the most frequently implicated culprits in indoor spider bites due to their wandering habits and tendency to build retreats in human-frequented areas like bedding and clothing.
Photography Tips
Use macro lenses with natural diffused lighting or a ring flash. Capture dorsal views to show the overall color and cephalothorax, and side angles to highlight the leg proportions.
User Notes
Found on door frame
Identified: 2026-10-08T21:44:40.484694