Yellow Sac Spider, Long-legged Sac Spider
Cheiracanthium inclusum (or Cheiracanthium mildei)
Miturgidae (Sac Spiders), Order Araneae. Key family characteristics include anterior spinnerets that are conical and contiguous, and two rows of similar-sized eyes.
Physical Description
The spider has an oval-shaped abdomen and a somewhat elongated cephalothorax. The body is smooth with fine, short hairs, lacking dramatic spikes or prominent humps. The front legs are noticeably longer than the others.
Size Estimate
Body length typically ranges from 5 to 10 millimeters, with a leg span of roughly 20 to 25 millimeters. The specimen appears to be an adult or sub-adult based on body proportions.
Coloration & Markings
Pale yellow, beige, or light greenish-tan overall, sometimes featuring a faint, darker longitudinal stripe running down the center of the abdomen. The jaws (chelicerae) often possess a slightly darker brownish tint.
Web Type
Sac spiders do not spin traditional orb or sheet webs for catching prey. Instead, they construct small, silken tubular sacs or retreats—often tucked into corners, ceilings, or under leaves—where they rest during the day.
Eye Arrangement
Eight eyes of roughly equal size arranged in two horizontal rows of four each across the front of the carapace.
Leg Characteristics
The legs are relatively long and slender, with the first pair noticeably longer than the fourth pair. They lack heavy spination or distinct banding, often held in a characteristic spread stance.
Venom & Safety Information
Venom Information
Contains a mild cytotoxic venom used to subdue invertebrate prey. It is not considered dangerously neurotoxic to humans, but protein components can cause localized discomfort.
Medical Significance
Low medical significance. Bites can cause immediate stinging pain, localized redness, and mild swelling, occasionally developing into a small blister similar to a mild bee sting. Serious systemic reactions are extremely rare.
Safety Recommendations
Shake out clothing and shoes left on the floor, seal entry points around windows and doors, and gently relocate indoor spiders outdoors using a cup and a piece of paper.
Habitat & Behavior
Habitat & Range
Found globally in temperate and subtropical regions, frequently adapting to human structures such as houses, garages, and sheds, as well as outdoor foliage, gardens, and grassy fields.
Behavior & Temperament
Active nocturnal hunters that leave their silken retreats at night to forage. They are generally defensive rather than aggressive, but will bite if trapped against human skin.
Diet & Prey
Primarily carnivorous, feeding on a wide range of small insects, including plant pests, flies, and other spiders, actively overpowering them rather than trapping them in a web.
Seasonal Activity
Most active during the warm spring and summer months, moving indoors more frequently in autumn as outdoor temperatures drop.
Description
The yellow sac spider is a common indoor and outdoor dweller known for its pale, unassuming coloration and active hunting habits. While frequently encountered in homes along upper walls and corners, it plays a valuable role in controlling household and garden insect populations.
Key Features
Pale yellow-to-greenish body color, the distinctive first pair of legs being significantly longer than the others, and the presence of a silken daytime retreat rather than an open web.
Similar Species
Recluse spiders (Loxosceles), which can be distinguished by their violin-shaped marking on the cephalothorax and a six-eyed arrangement instead of the eight equal eyes found on sac spiders.
Life Cycle
Females construct silken egg sacs in secluded areas during late spring or summer, laying several dozen eggs. Spiderlings hatch and molt multiple times, typically completing their life cycle within a single year.
Ecological Importance
Acts as an effective natural pest controller in agricultural fields, orchards, and residential gardens by preying on herbivorous insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed globally.
Interesting Facts
Yellow sac spiders are notorious for building their silken retreats inside the fuel systems of certain automobiles, sometimes clogging vapor canisters and leading to automotive recalls.
Photography Tips
Use a macro lens with good side lighting to highlight the eye arrangement and leg proportions. Maintain a safe distance and photograph against a neutral background for clarity.
Identified: 2026-09-10T03:31:02.895642