Yellow Sac Spider, Long-legged Sac Spider, Mild's Sac Spider
Cheiracanthium mildei
Cheiracanthiidae (Sac Spiders), Order Araneae. They are known for building silken sacs for resting rather than webs for hunting.
Physical Description
A small-to-medium spider with a slightly translucent, 'silky' appearance. The cephalothorax is often a pale greenish-yellow or tan, while the abdomen is oval-shaped and can appear slightly more yellow or beige depending on recent diet. The chelicerae (mouthparts) are notably dark and prominent.
Size Estimate
Body length typically ranges from 5 to 10 mm (approx. 0.2 to 0.4 inches), with a total leg span reaching up to 25 mm (1 inch). This appears to be an adult specimen.
Coloration & Markings
Uniform pale yellow, cream, or light tan coloration. A faint darker longitudinal stripe may be visible on the abdomen. A distinguishing feature is the dark brown to black 'socks' or tips on the ends of the legs.
Web Type
Does not build a traditional capture web. Instead, it spins a small, white, flattened silken tube or 'sac' in corners, wall/ceiling junctions, or behind furniture to hide during the day.
Eye Arrangement
Eight eyes arranged in two horizontal rows of four. The eyes are relatively small and equal in size, typical of many hunting spiders.
Leg Characteristics
Long, slender legs with the first pair being longer than the rest. The tarsi (feet) end in dark, distinct tips or 'socks'. The legs are covered in fine hairs but lack heavy spines.
Venom & Safety Information
Venom Information
Contains a mild necrotizing component. Historically blamed for necrotic skin lesions, though recent scientific evidence suggests their venom is not as potent as the Brown Recluse and rarely causes significant tissue death.
Medical Significance
Moderate. Bites can be painful, similar to a bee sting, and may cause localized swelling, redness, and itching. Symptoms usually resolve within 72 hours. In rare cases, systemic reactions like nausea may occur. It is NOT considered dangerous to healthy adults.
Safety Recommendations
To avoid bites, shake out clothing or shoes left on the floor. If found, they can be safely relocated using the cup-and-paper method. Bites should be cleaned with soap and water; apply ice for swelling.
Habitat & Behavior
Habitat & Range
Widespread throughout North America (where it is an introduced species from Europe) and most of Europe. Commonly found inside homes and buildings, but also inhabits gardens, trees, and shrubs.
Behavior & Temperament
An active nocturnal hunter that wanders to find prey. During the day, it stays inside its silk sac. While generally shy, they are known to be slightly more prone to biting than other common household spiders if trapped against skin or disturbed.
Diet & Prey
Primarily feeds on small insects, other spiders, and insect eggs. They are beneficial for indoor pest control, consuming flies, moths, and agricultural pests.
Seasonal Activity
Active year-round indoors. Outdoors, they are most visible from spring through autumn, with mating peaks in late summer.
Description
The Yellow Sac Spider is a common, pale-colored indoor resident often seen wandering on walls or ceilings at night. Its translucent body and dark-tipped feet make it easily recognizable to the observant homeowner. As an agile hunter, it plays a vital role in controlling indoor insect populations without the use of messy webs for food capture.
Key Features
Pale yellow/tan translucent body, long front legs, dark-tipped 'socks' on feet, and the presence of small white silk retreat sacs in room corners.
Similar Species
Rotund sac spiders (Clubiona spp.) and the Brown Recluse (Loxosceles reclusa). It lacks the distinct fiddle shape of the recluse and has different eye arrangements.
Life Cycle
Females lay 30-48 eggs within a white silk sac and often stay to guard them. Spiderlings emerge and eventually balloon or crawl away. Lifespan is generally 1-2 years.
Ecological Importance
Acts as a natural pest control agent in both indoor and agricultural environments, consuming various nuisance insects.
Conservation Status
Not evaluated (IUCN), but populations are stable and widespread; they are considered synanthropic (living in close association with humans).
Interesting Facts
Cheiracanthium mildei is known for being attracted to the smell of volatiles in gasoline, occasionally causing issues by spinning webs in car fuel system vent lines.
Photography Tips
The best angle is a top-down (dorsal) shot to show the leg lengths and abdominal stripe. Use macro mode to capture the dark-tipped feet and mouthparts for definitive ID.
Identified: 2026-07-07T14:14:59.020026