Black-footed Yellow Sac Spider, American Yellow Sac Spider
Cheiracanthium inclusum
Eutichuridae (Sac Spiders), Order Araneae. Formerly placed in Miturgidae or Clubionidae. Characterized by conical anterior spinnerets and eight eyes of similar size arranged in two rows.
Physical Description
The spider has a compact body with a smooth, oval-shaped abdomen and a slightly narrower cephalothorax. The proportions feature moderately long legs and a pale, uniform texture without prominent spines.
Size Estimate
Body length ranges from 5 to 9 millimeters for females and slightly smaller for males, with a total leg span of approximately 20 to 25 millimeters. This specimen appears to be an adult or sub-adult.
Coloration & Markings
The base coloration is pale yellow, yellowish-green, or beige. The abdomen often features a faint, darker longitudinal cardiac stripe. In some species of this genus, the tips of the feet (tarsi) appear darker, giving rise to the common name.
Web Type
Sac spiders do not spin traditional prey-catching webs. Instead, they construct small, silken retreats, usually shaped like a flattened tube or sac, tucked away in corners, under bark, or within folded leaves, where they rest during the day.
Eye Arrangement
Eight eyes of roughly equal size arranged in two relatively straight horizontal rows across the front of the carapace.
Leg Characteristics
Legs are moderately long and slender, with the first pair typically longer than the fourth pair in many species of this genus, used actively for tactile exploration and prey capture.
Venom & Safety Information
Venom Information
Contains cytotoxins used to immobilize insect prey. While historically reputed to cause necrotic lesions, modern medical consensus indicates bites typically result in localized pain, redness, and mild swelling akin to a wasp sting.
Medical Significance
Low medical significance. Bites are uncommon unless the spider is compressed against the skin (such as being trapped in clothing or bedding). Symptoms are localized and resolve within a few days without serious complications.
Safety Recommendations
Shake out shoes and clothing left on the floor, seal entry points around windows and doors, and gently relocate wandering individuals outdoors using a cup and paper.
Habitat & Behavior
Habitat & Range
Widespread across North and South America. Prefers foliage, tall grasses, shrubs, and often enters human habitations during autumn seeking shelter, frequently found high up on walls or ceilings.
Behavior & Temperament
Active nocturnal hunters that roam freely rather than waiting in a web. They are generally defensive if trapped or pressed against the skin, which can result in a defensive bite.
Diet & Prey
Carnivorous predators feeding on a wide variety of small insects, including agricultural pests, flies, aphids, and other spiders, using active stalking and swift pounces.
Seasonal Activity
Most active during late spring through autumn, with indoor sightings peaking in late summer and autumn as temperatures drop and individuals seek overwintering shelter.
Description
The Yellow Sac Spider is a nimble, pale-colored nocturnal hunter frequently encountered indoors as seasons change. Recognized by its yellowish-green body and daytime silken retreats, it plays an effective role in natural pest control around gardens and homes.
Key Features
Pale yellow-green coloration, elongated oval abdomen often with a faint central stripe, first pair of legs noticeably longer, and the habit of resting inside a papery silken sac during the day.
Similar Species
Other sac spiders such as Cheiracanthium mildei (European yellow sac spider), which looks very similar and is also commonly found in buildings. Separation often requires microscopic examination of genital structures.
Life Cycle
Females construct silken egg sacs in protected retreats during late spring or summer, depositing several dozen eggs. Spiderlings hatch and disperse, undergoing multiple molts to reach maturity, with a typical lifespan of about one year.
Ecological Importance
Acts as an effective generalist predator in agricultural fields and residential gardens, helping to regulate populations of herbivorous insects and other arthropods.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed across their natural range.
Interesting Facts
Yellow sac spiders are among the most common biters of humans indoors, largely because they wander actively across walls and ceilings and easily get trapped in clothes or bedding.
Photography Tips
Use macro lenses with adequate lighting against a neutral background. Because they are fast-moving, a fast shutter speed is recommended to capture clear diagnostic details of the cephalothorax and legs.
Identified: 2026-08-30T14:53:24.671200