Yellow Sac Spider, Long-legged Sac Spider, Northern Yellow Sac Spider
Cheiracanthium mildei
Cheiracanthiidae (Sac Spiders), Order Araneae
Physical Description
A medium-sized spider with a slightly elongated cephalothorax and an oval-shaped abdomen. The body is relatively smooth with very fine hairs, giving it a slightly translucent or waxy sheen. Its most prominent features are the relatively long, slender legs and the prominent, dark-tipped chelicerae (fangs).
Size Estimate
Body length usually ranges from 5 to 10 mm (0.2 to 0.4 inches), with a leg span reaching up to 25 to 30 mm. This specimen appears to be an adult.
Coloration & Markings
Characterized by a pale yellowish to light tan or greenish body color. The cephalothorax is often a slightly darker shade than the abdomen. It lacks distinct markings like stripes or spots, though the 'heart mark' (a faint longitudinal line on the upper abdomen) may be visible. The ends of the legs (tarsi) and the mouthparts are typically darker.
Web Type
Does not build traditional capture webs. Instead, it constructs a small, white, silk 'sac' or retreat in corners, under leaves, or in crevices to hide during the day or to protect egg sacs.
Eye Arrangement
Contains eight eyes arranged in two horizontal rows of four. The rows are relatively straight, which helps distinguish them from other families like clubionids.
Leg Characteristics
The legs are long and slender. Specifically, the first pair of legs is significantly longer than the others, which is a key diagnostic trait for the genus Cheiracanthium. The feet have dense claw tufts allowing them to walk easily on smooth surfaces like ceilings.
Venom & Safety Information
Venom Information
Contains a mild cytotoxic venom. For many years, they were falsely accused of causing necrotic lesions similar to brown recluse bites, but modern research has largely debunked this, showing their venom is much less potent.
Medical Significance
Considered moderately medically significant. Bites are generally painful (comparable to a bee sting) with localized swelling and redness. While most symptoms resolve within 72 hours, some individuals may experience slight systemic symptoms like nausea, but true necrosis is rare.
Safety Recommendations
To avoid bites, shake out clothing or shoes left on the floor and use caution when reaching into dark corners. If found, they can be easily relocated using the 'cup and paper' method. Bitten areas should be cleaned with soap and water; seek medical help only if severe allergic reactions or unusual skin breakdown occurs.
Habitat & Behavior
Habitat & Range
Commonly found throughout North America and Europe. They are highly synanthropic, meaning they frequently live in and around human structures, often found near ceilings, window frames, and behind furniture.
Behavior & Temperament
An active nocturnal hunter that leaves its silk retreat at night to search for prey. They are quick and agile. While not naturally aggressive, they are known to bite if trapped against skin (e.g., inside clothing or bedding).
Diet & Prey
Generalist predator feeding on a variety of small insects and other spiders. They use their speed and strong chelicerae to overpower prey without the use of a web.
Seasonal Activity
Active year-round indoors, but most frequently noticed in late summer and autumn as they move indoors or enter homes seeking warmth and mates.
Description
The Yellow Sac Spider is a pale, elegant nocturnal wanderer frequently encountered in homes. It is easily recognized by its straw-colored body and long font legs. During the day, it rests in a silken tube, emerging at night to sprint across walls and ceilings in search of small insect prey, playing a vital role in indoor pest control.
Key Features
Pale yellow/tan color, first pair of legs notably longer than others, dark-tipped fangs, and the presence of small silk retreats in wall corners.
Similar Species
Often confused with the Brown Recluse (Loxosceles reclusa), but lacks the 'violin' marking and has a different eye arrangement. Also resembles ghost spiders (Anyphaenidae) and other sac spiders (Clubionidae).
Life Cycle
Females lay eggs inside a reinforced silk retreat and guard them until they hatch. Spiderlings may stay with the mother for a short period before dispersing. They typically live for about one year.
Ecological Importance
Act as significant biological control agents for agricultural pests (like fruit flies and leafhoppers) and common household pests.
Conservation Status
Not evaluated by the IUCN; widespread and common with stable populations.
Interesting Facts
Formerly placed in the family Miturgidae and Clubionidae, DNA evidence moved them to their own family. They are famous for being attracted to the smell of gasoline, sometimes building nests in the vent pipes of vehicles, which led to a famous Mazda recall in 2011.
Photography Tips
Focus on the front of the spider to capture the eye arrangement and the length of the first pair of legs. Side profile shots are useful to show the 'scopy' (hairs) on the feet and the silk retreat if present.
Identified: 2026-07-04T06:46:59.774134