Yellow Sac Spider, Long-legged Sac Spider, Pale Leaf-roller
Cheiracanthium mildei
Cheiracanthiidae (Sac Spiders), Order Araneae. Characterized by building silk retreats rather than prey-catching webs.
Physical Description
A small spider with a somewhat translucent, cylindrical abdomen and a slightly darker cephalothorax. The body is relatively smooth with very fine hairs, giving it a slightly glossy or velvety appearance. The fangs and mouthparts (chelicerae) are often noticeably darker than the rest of the body.
Size Estimate
Body length is typically 5-10mm (0.2-0.4 inches). With legs extended, the total span is approximately 25-30mm. This specimen appears to be an adult.
Coloration & Markings
Predominantly pale yellow, cream, or light tan, often with a faint greenish or greyish tint. It lacks distinct stripes or spots, but usually has a darker vertical 'heart mark' on the anterior dorsal abdomen and dark-tipped 'toes' (tarsal claws).
Web Type
None for hunting. It constructs a small, white, flattened silk tube or 'sac' in corners, wall-ceiling junctions, or behind furniture for resting during the day and for egg-laying.
Eye Arrangement
Eight eyes in two horizontal rows. All eyes are roughly the same size and appear as small dark beads. The arrangement is fairly uniform across the front of the cephalothorax.
Leg Characteristics
Long, slender legs. The first pair of legs is significantly longer than the others, which is a diagnostic feature. The legs appear translucent and end in dark-colored tips.
Venom & Safety Information
Venom Information
Contains a mild cytotoxin. While historically and incorrectly blamed for necrotic lesions similar to brown recluse bites, modern research indicates the venom generally causes localized reactions.
Medical Significance
Low to Moderate. Bites are painful (similar to a bee sting) and can cause localized swelling, redness, and itching. Symptoms usually resolve within 72 hours. Not considered dangerous to healthy humans.
Safety Recommendations
To avoid bites, shake out clothing or bedding left on the floor. If relocation is desired, use the cup-and-paper method. Bites should be cleaned with soap and water; apply ice for swelling.
Habitat & Behavior
Habitat & Range
Found globally but very common in North America and Europe. In houses, they prefer the junctions of walls and ceilings, closets, and window frames. Outside, they live in foliage, shrubs, and under bark.
Behavior & Temperament
A nocturnal active hunter that wanders away from its sac at night to search for prey. They are agile and quick. Generally shy and will retreat, but they are known for being occasionally 'nippy' if trapped against skin or disturbed in their silk sac.
Diet & Prey
Generalist predators feeding on small insects, other spiders, and insect eggs. They do not use a web to catch prey; they overpower it with speed and their relatively potent venom.
Seasonal Activity
Visible year-round indoors. Population peaks in late summer and autumn as they move further indoors to seek warmth or find mates.
Description
The Yellow Sac Spider is one of the most common indoor spiders worldwide. Easily recognized by its pale, ghostly coloration and its habit of resting in silk tubes at the corners of ceilings, it is a beneficial predator of indoor pests like flies and gnats.
Key Features
Pale yellow/cream translucent body, long first pair of legs, dark chelicerae, and the absence of any patterned markings on the abdomen.
Similar Species
Often confused with the Brown Recluse (Loxosceles reclusa), but lacks the 'violin' mark and has different eye arrangements. Also similar to Ghost Spiders (Anyphaenidae).
Life Cycle
Females lay eggs inside a silk retreat/sac and guard them until they hatch. Spiderlings may stay with the mother for a short period before dispersing. Lifespan is approximately one year.
Ecological Importance
Significant indoor pest controller, reducing populations of fungus gnats, fruit flies, and other small household insects.
Conservation Status
Not evaluated by IUCN; considered stable and very common. Often considered an invasive or introduced species in many parts of the world.
Interesting Facts
In the automotive industry, these spiders became famous for weaving silk sacs inside the fuel system vent lines of certain car models, leading to mechanical recalls.
Photography Tips
Focus on the front of the spider to capture the long front legs and darker mouthparts. Use a macro setting to show the eye arrangement for definitive ID.
User Notes
Found on ceiling in house
Identified: 2026-06-27T17:21:46.643703