Yellow Sac Spider, Black-footed Spider
Cheiracanthium mildei / Cheiracanthium inclusum
Cheiracanthiidae (Yellow Sac Spiders), Order Araneae
Physical Description
Small, slender spiders with a slightly translucent, elongated abdomen. The cephalothorax is typically a pale tan or greenish-yellow, and the body has a smooth, satin-like texture without prominent hairs. The abdomen often has a faint cardiac mark (a darker line) running down the center.
Size Estimate
Body length 5-10 mm; leg span 15-25 mm. The specimen in the image appears to be an adult.
Coloration & Markings
Pale yellow, cream, or light tan to greenish-yellow. They often have dark 'feet' (tarsi) which give them the nickname 'black-footed spider'. They lack complex patterns, though some may show a darker dorsal stripe.
Web Type
They do not build hunting webs. Instead, they construct small, silk retreat sacs (resembling cocoons) in corners, crevices, or leaves where they rest during the day.
Eye Arrangement
Eight eyes in two horizontal rows. Front row is relatively straight; back row is slightly wider. Eyes are small and of similar size, typical of nocturnal active hunters.
Leg Characteristics
The front pair of legs is significantly longer than the others. Legs are slender and the tips are noticeably darker due to dense, dark hairs (scopulae) used for climbing smooth surfaces.
Venom & Safety Information
Venom Information
Cytotoxic venom. Historically incorrectly blamed for necrotic lesions similar to brown recluse bites; however, modern research shows the venom causes localized pain and swelling but rarely results in necrosis.
Medical Significance
Mildly significant. Bites are painful (sharper than a bee sting) and can cause localized swelling, redness, and itching. Symptoms usually resolve in 72 hours. Not considered dangerous to healthy humans.
Safety Recommendations
If found, they can be safely relocated using the cup-and-paper method. To prevent bites, shake out clothing and shoes left on the floor and clear away silk sacs found in room corners with a vacuum.
Habitat & Behavior
Habitat & Range
Found worldwide. C. mildei is common in homes across North America and Europe, while C. inclusum is more common outdoors in gardens, high grass, and shrubs.
Behavior & Temperament
Nocturnal active hunters that emerge at night to forage. They are agile and quick. While not aggressive, they are known to bite if trapped against skin or disturbed in their retreats.
Diet & Prey
Generalist predators feeding on small insects, other spiders, and insect eggs. They hunt by wandering rather than sitting in a web.
Seasonal Activity
Active year-round indoors, but most visible in autumn when they search for mates or enter homes to find overwintering spots.
Description
This pale, active hunter is a common sight in human dwellings. With its yellowish translucent body and exceptionally long front legs, it is easily identified as it scuttles across walls and ceilings at night. Its 'sac' name comes from the silken sleeping bags it builds in high corners or behind furniture.
Key Features
Pale yellow color, black-tipped feet, front legs longer than second pair, and presence of silken retreat sacs in corners.
Similar Species
Brown Recluse (Loxosceles reclusa) - lacking the violin mark; Ghost Spiders (Anyphaenids) - which have different abdominal patterns and tracheal spiracle placement.
Life Cycle
Females produce several egg sacs throughout late summer and autumn, often guarding them inside a silk retreat. The spiderlings may remain in the mother's retreat for a short time after hatching.
Ecological Importance
Highly beneficial as natural pest control, consuming a wide variety of indoor and garden pests like flies, moths, and smaller spiders.
Conservation Status
Not evaluated; widespread and common with stable populations.
Interesting Facts
They are known for their ability to run quickly across vertical surfaces and ceilings. Interestingly, they have been documented attraction to the scent of gasoline, leading to them building nests in vehicle fuel systems.
Photography Tips
Focus on the front legs and the 'face' (eyes). Side-angle shots are best to capture the translucent quality of the body and the dark tips of the legs.
Identified: 2026-06-17T13:13:39.202793