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, conical anterior spinnerets, and a wandering nocturnal lifestyle.
Physical Description
The spider features an oval-shaped abdomen and a slightly longer cephalothorax. The texture is relatively smooth with fine hairs. Females and males are similar in general appearance, though males tend to have slightly longer legs and a more slender abdomen.
Size Estimate
Body length ranges from 5 to 10 millimeters, with a total leg span of roughly 20 to 25 millimeters. This specimen appears to be an adult or sub-adult.
Coloration & Markings
Pale yellow, yellowish-green, or beige overall, often with a darker brownish-green cardiac stripe running down the top of the abdomen. There are generally no complex patterns or bold markings.
Web Type
Does not build traditional capture webs. Instead, it constructs a flattened, silken retreat or sac (often in corners of ceilings, under logs, or behind objects) where it rests during the day.
Eye Arrangement
Eight small, dark eyes arranged in two relatively parallel horizontal rows of four, all of similar size.
Leg Characteristics
The first pair of legs is noticeably longer than the others, which is a key diagnostic feature of sac spiders. Legs are slender, taper to fine points, lack prominent spination, and have no distinct banding.
Venom & Safety Information
Venom Information
Cytotoxic venom used to subdue insect prey. While it causes localized pain and occasionally a small necrotic lesion in rare sensitive individuals, it is generally mild.
Medical Significance
Minor medical significance. Bites can cause immediate stinging pain, redness, and swelling, sometimes developing into a small blister, but severe systemic effects are rare.
Safety Recommendations
Keep clothing and shoes off the floor, shake out items before use, seal entry points around windows and doors, and gently relocate individuals outdoors using a cup and card if found inside.
Habitat & Behavior
Habitat & Range
Found widely across North and South America (and introduced globally in various temperate regions). Prefers foliage, tall grass, gardens, and frequently enters human dwellings in autumn seeking shelter.
Behavior & Temperament
Active nocturnal hunters that roam away from their daytime silken retreats in search of prey. They are defensive if cornered or squeezed against human skin, which can lead to defensive bites.
Diet & Prey
Feeds primarily on a wide variety of soft-bodied insects, pests, and occasionally other spiders, hunting them down actively rather than trapping them.
Seasonal Activity
Most active during late spring through autumn. They frequently wander indoors during late summer and autumn as temperatures drop.
Description
The Yellow Sac Spider is a common and agile hunter frequently encountered indoors during the cooler months. Recognized by its pale yellowish-green body and noticeably longer front legs, it spends its days hidden inside small silken tubes tucked into wall corners or under objects, emerging at night to forage for pest insects.
Key Features
Pale yellow-green coloration, prominent first pair of legs that are longer than the rest, absence of strong markings, and the habit of resting in a small silken sac during the day.
Similar Species
Other wandering spiders such as ghost spiders (Anyphaenidae) or juvenile wolf spiders (Lycosidae). Ghost spiders look similar but have a spiracle visible on the underside of the abdomen, while wolf spiders have a distinct eye arrangement with a large posterior pair.
Life Cycle
Females construct a silken sac to lay eggs in during the spring or summer, guarding the egg sac until the spiderlings hatch. They undergo multiple molts, reaching maturity in roughly one year.
Ecological Importance
Acts as an effective natural pest control agent in agricultural fields, orchards, and home gardens by consuming large numbers of herbivorous insects.
Conservation Status
Not evaluated by the IUCN, but populations are abundant, widespread, and secure globally.
Interesting Facts
Yellow sac spiders are among the most common biters of humans indoors, usually occurring when the spider is accidentally trapped against the skin while resting in clothing or bedding.
Photography Tips
Use macro photography with natural side lighting or a diffused flash to capture the eye arrangement and leg proportions accurately. Maintain a safe distance to avoid startling the spider into fleeing.
Identified: 2026-08-21T17:09:30.971215