Yellow Sac Spider, Long-legged Sac Spider
Cheiracanthium inclusum (or Cheiracanthium mildei)
Miturgidae (Sac Spiders), Order Araneae. Key family characteristics include eight similar eyes in two rows and conical anterior spinnerets.
Physical Description
Small to medium-sized spider with a pear-shaped, slightly elongated abdomen and a robust cephalothorax. The body is relatively smooth with fine hairs, lacking dramatic spines, and features prominent, darkened chelicerae.
Size Estimate
Body length typically ranges from 5 to 10 mm, with a leg span of around 20 to 25 mm. This appears to be an adult or sub-adult specimen.
Coloration & Markings
Pale yellow, yellowish-green, or beige overall, often with a faint darker dorsal stripe running down the center of the abdomen. The tips of the jaws and the mouthparts are often brownish.
Web Type
Sac spiders do not build traditional capture webs. Instead, they construct a small, flattened silken tube or sac, usually in a corner, ceiling junction, or under loose bark, where they rest during the day.
Eye Arrangement
Eight small eyes of roughly equal size arranged in two nearly parallel horizontal rows across the front of the cephalothorax.
Leg Characteristics
Legs are relatively long, slender, and somewhat forward-facing, with the first pair of legs noticeably longer than the others, which is a key diagnostic feature for this group.
Venom & Safety Information
Venom Information
Produces a cytolytic venom primarily used to immobilize insect prey. Their bites can cause localized pain, redness, and swelling.
Medical Significance
Minimally medically significant. Bites can be painful and occasionally result in a small lesion or blister, but systemic symptoms are rare and usually resolve without medical intervention.
Safety Recommendations
Avoid handling with bare hands; gently cup and release individuals found indoors. Shake out shoes and clothing left on the floor before wearing.
Habitat & Behavior
Habitat & Range
Found globally in temperate and tropical regions. In natural settings, they inhabit foliage, grass, and under tree bark; indoors, they are commonly found wandering along walls and ceilings in homes.
Behavior & Temperament
Nocturnal active hunters that leave their silken retreat at night to forage. They are generally defensive if cornered or trapped against the skin.
Diet & Prey
Carnivorous, feeding on a wide variety of small insects and other spiders. They subdue prey using speed and venom rather than a trap web.
Seasonal Activity
Most active during spring and summer months, often moving indoors in late summer and autumn as outdoor temperatures drop.
Description
The Yellow Sac Spider is a frequent indoor wanderer known for its pale yellowish hue and tendency to build silken retreat sacs in room corners. As an agile nocturnal hunter, it plays a useful role in reducing indoor insect populations, though its defensive nature means accidental compression against human skin can result in a sharp bite.
Key Features
Pale yellow or greenish body color, first pair of legs noticeably longer than the others, lack of prominent contrasting patterns, and the presence of a silken daytime retreat sac.
Similar Species
Can be confused with ghost spiders (Anyphaenidae) or juvenile wandering spiders, but distinguished by the specific eye arrangement and the exceptionally long first pair of legs.
Life Cycle
Females construct silken egg sacs in protected areas during warmer months, depositing several dozen eggs. Spiderlings hatch and disperse, undergoing multiple molts to reach maturity within a year.
Ecological Importance
Acts as an effective generalist predator helping to control populations of flies, mosquitoes, and other household or agricultural insect pests.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and abundant globally.
Interesting Facts
Yellow sac spiders are among the most common spiders found inside human dwellings, yet they spend most of their lives hidden inside their secretive silken retreats.
Photography Tips
Use macro lenses with good lighting to capture the eye arrangement and the distinctively long first leg pair. Photograph against a neutral background from a safe distance.
Identified: 2026-10-13T01:02:21.592392