Yellow Sac Spider, Long-legged Sac Spider
Cheiracanthium inclusum (or Cheiracanthium mildei)
Eutichuridae (Sac Spiders), Order Araneae. Formerly placed in Miturgidae or Clubionidae. Key family characteristics include eight similar eyes in two rows, conical anterior spinnerets close together, and a wandering, non-web-spinning habit during the night.
Physical Description
The body is typically slender and oval-shaped with a pale cephalothorax and abdomen. The surface is sparsely covered in fine setae. There is little prominent sexual dimorphism other than the male's slightly more slender abdomen and longer palps. They lack distinct contrasting bands, maintaining a uniform, pale appearance.
Size Estimate
Body length ranges from 5 to 10 millimeters, with a leg span of approximately 20 to 25 millimeters. The specimen shown appears to be a typical subadult or adult wandering sac spider.
Coloration & Markings
Pale yellow, beige, or light tan overall, occasionally displaying a faint, darker greenish-grey cardiac stripe running down the dorsal surface of the abdomen. The chelicerae and tips of the legs may sometimes show a slightly darker brownish tinge.
Web Type
Does not build a traditional prey-catching web. Instead, they construct small, silken tubular sacs or retreats—often tucked into rolled leaves, under bark, or in corners of walls and ceilings—where they rest during the day or guard eggs.
Eye Arrangement
Eight eyes of roughly equal size, arranged in two horizontal rows of four each across the front of the carapace.
Leg Characteristics
Long, slender legs with the first pair of legs noticeably longer than the rest (a defining feature of the genus). They have distinct dark claws and lack heavy spination or prominent banding, typically held flat against surfaces when resting.
Venom & Safety Information
Venom Information
Contains cytotoxic venom used to subdue invertebrate prey. While historically linked to necrotic lesions, modern medical consensus suggests bites typically result in localized pain, redness, and swelling, akin to a wasp sting, without true necrosis.
Medical Significance
Minor medical significance. Bites are painful and can occasionally cause localized inflammation, mild systemic reactions, or a small blister, but they are rarely dangerous and resolve on their own without severe complications.
Safety Recommendations
Seal entry points to homes, shake out clothing or gear left outdoors, and safely relocate indoor spiders using a container and piece of paper rather than handling them directly.
Habitat & Behavior
Habitat & Range
Found across North America, Europe, and various temperate regions globally. Prefers foliage, tall grasses, orchards, and frequently enters human structures, vehicles, and warehouses, especially during autumn or when seeking shelter.
Behavior & Temperament
Nocturnal active hunters. During the day, they remain hidden inside their silken retreat sacs. They can be defensive if cornered, trapped against the skin, or when defending an egg sac, and are known to bite readily under such conditions.
Diet & Prey
Carnivorous generalist predator. Feeds on a wide variety of small insects, agricultural pests, and other spiders by actively stalking and subduing them rather than using a web.
Seasonal Activity
Most active during the warm spring and summer months, with increased indoor sightings in late summer and autumn as temperatures drop and they seek overwintering shelter.
Description
The yellow sac spider is a common, pale-colored wandering hunter frequently encountered in gardens and indoor spaces. Known for building small silken retreat sacs rather than capture webs, this agile nocturnal predator plays an important role in controlling pest insect populations around homes and agricultural fields.
Key Features
Uniform pale yellow-tan coloration, noticeably elongated first pair of legs, lack of striking abdominal patterns, and the habit of resting inside a silken daytime retreat tube.
Similar Species
Ghost spiders (Anyphaenidae) and Clubionid sac spiders, which share a similar pale coloration and wandering habit but differ subtly in tracheal spiracle placement and eye morphology.
Life Cycle
Females construct silken egg sacs in spring or early summer containing dozens of eggs. After hatching, spiderlings disperse or remain near the maternal retreat. They undergo multiple molts to reach maturity, with a typical lifespan of about one year.
Ecological Importance
Serves as an effective biological control agent by consuming large numbers of agricultural and household insect pests, while also acting as prey for birds, small mammals, and larger arachnids.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and highly adaptable to human-modified environments.
Interesting Facts
Yellow sac spiders are frequently found inside automobiles—as seen here resting on a tire—attracted by the enclosed spaces or shelter provided by vehicle undercarriages.
Photography Tips
Use macro lenses or smartphone macro settings with natural side lighting to highlight the leg proportions and pale coloration against contrasting backgrounds without disturbing the spider.
Identified: 2026-10-05T15:33:31.038470