American Yellow Sac Spider
Cheiracanthium inclusum
Miturgidae (Prowling Spiders), Order Araneae
Physical Description
The spider has a smooth, oval-shaped abdomen and a well-defined cephalothorax with distinct thoracic grooves. Its body is moderately robust with forward-facing chelicerae.
Size Estimate
Body length typically ranges from 5 to 9 mm, with a leg span of approximately 20 to 25 mm. This specimen appears to be an adult.
Coloration & Markings
Pale yellow to yellowish-green body with a distinct darker brownish-gray cardiac stripe running down the center of the dorsal abdomen. The tips of the chelicerae and mouthparts often show a brownish tint.
Web Type
Does not build a traditional orb or sheet web. Instead, it constructs a silken retreat or sac, typically in curled leaves, under loose bark, or in corners of walls and ceilings where it rests during the day.
Eye Arrangement
Eight eyes arranged in two parallel rows of four, all relatively equal in size, typical of the miturgid family.
Leg Characteristics
Long, slender legs with the first pair noticeably longer than the others, featuring distinct dark claws at the tips. The legs lack prominent spines but possess fine hairs.
Venom & Safety Information
Venom Information
Contains a cytotoxic venom used to subdue small insect prey. It is not considered medically significant to humans, though a bite can cause localized pain and redness.
Medical Significance
Low medical danger. Bites usually result in mild, temporary localized pain, swelling, and itching similar to a wasp sting, subsiding within a few days.
Safety Recommendations
Avoid direct handling. If found indoors, gently guide it into a container using a piece of paper and release it outside. Seal cracks and use door sweeps to keep them out.
Habitat & Behavior
Habitat & Range
Widely distributed across North, Central, and South America. Found in foliage, grass, gardens, and frequently enters human structures, especially in autumn.
Behavior & Temperament
Nocturnal hunter that actively forages for prey away from its daytime silken retreat. It can be defensive if trapped or pressed against the skin.
Diet & Prey
Carnivorous, feeding on a wide variety of small insects, agricultural pests, and other spiders using active hunting and quick grasping techniques.
Seasonal Activity
Most active during late spring, summer, and early autumn, often moving indoors as cooler weather approaches.
Description
The American Yellow Sac Spider is a common nocturnal hunter easily recognized by its pale yellow-green hue and distinctive abdominal stripe. Often found resting in silken sacs in homes or gardens, it plays a beneficial role in controlling insect populations while occasionally surprising homeowners.
Key Features
Pale yellow-green coloration, prominent dark dorsal cardiac stripe, elongated first pair of legs, and the habit of resting inside a small silken sac.
Similar Species
Other sac spiders such as Cheiracanthium mildei, which looks nearly identical and requires microscopic examination of genital structures for definitive separation.
Life Cycle
Females construct silken egg sacs in protected retreats containing around 30 to 50 eggs. Mating occurs in spring or summer, and the spiderlings emerge after a few weeks, molting multiple times as they grow.
Ecological Importance
Serves as an effective generalist predator helping to regulate populations of agricultural pests and garden insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure and widespread across its native range.
Interesting Facts
Yellow sac spiders are notorious for being attracted to the chemical scent of certain hydrocarbons, leading them to occasionally build webs inside automobile fuel system components and block vents.
Photography Tips
Use macro lenses with adequate natural lighting or a diffused flash to capture the subtle yellow-green tones and eye arrangement without disturbing the spider.
Identified: 2026-10-03T17:55:08.480934