Broad-faced Sac Spider
Trachelas pumilus (or similar Trachelas species)
Corinnidae (Sac Spiders), Order Araneae. Key family characteristics include eight eyes in two rows, robust legs, and a habit of constructing silken retreats.
Physical Description
The spider has a distinctively robust, oval abdomen and a dark, wide cephalothorax. The body appears smooth and shiny with a compact structure, featuring enlarged chelicerae.
Size Estimate
Body length is estimated around 4 to 8 millimeters with a leg span of approximately 15 to 25 millimeters, consistent with an adult or sub-adult sac spider.
Coloration & Markings
Characterized by a deep reddish-brown to dark orange cephalothorax and chelicerae, contrasting with a paler grayish or brownish-yellow abdomen.
Web Type
Does not build a traditional capture web. Instead, it constructs a flattened, silken retreat or sac in crevices, under bark, or along wall corners where it rests during the day.
Eye Arrangement
Eight eyes arranged in two rows of four, typical of corinnid and clubionid sac spiders, with eyes being relatively equal in size.
Leg Characteristics
Legs are robust and moderately short, lacking heavy spination but equipped with paired claws and claw tufts for gripping smooth surfaces.
Venom & Safety Information
Venom Information
Contains mild cytotoxic venom used primarily to immobilize small insect prey. Not considered dangerous to humans, though a bite may cause minor localized pain.
Medical Significance
Harmless to humans. Bites are rare and typically occur only when the spider is pressed directly against the skin. Symptoms usually consist of mild, temporary stinging and redness.
Safety Recommendations
Safely relocate wandering individuals outdoors using a glass and a piece of card. Shake out shoes and clothing left on the floor to avoid accidental bites.
Habitat & Behavior
Habitat & Range
Found across North America and various temperate regions globally. Prefers foliage, under bark, woodpiles, and frequently wanders indoors into homes, particularly in autumn.
Behavior & Temperament
Nocturnal active hunter that leaves its silken retreat at night to forage for prey. Generally docile unless trapped or cornered against the skin.
Diet & Prey
Feeds primarily on small insects, including flies, aphids, and other spiders, capturing them through active stalking rather than using a web.
Seasonal Activity
Most commonly seen indoors during late summer and autumn as dropping temperatures drive them to seek shelter inside buildings.
Description
A small, swift nocturnal wanderer commonly encountered in homes during seasonal changes. Recognized by its shiny dark head and pale abdomen, it plays a helpful role in household pest control.
Key Features
Distinctive dark, reddish-brown broad cephalothorax, robust chelicerae, contrasting pale abdomen, and absence of an orb web.
Similar Species
Other sac spiders such as Cheiracanthium mildei (Yellow Sac Spider), which are typically paler yellow-green without the dark reddish head contrast.
Life Cycle
Mates in spring or summer, after which females construct a silken egg sac containing dozens of eggs, guarding them until they hatch into spiderlings that disperse via ballooning.
Ecological Importance
Acts as an effective natural predator of small agricultural and household insect pests, helping to regulate local insect populations.
Conservation Status
Not evaluated by the IUCN, but populations are stable, widespread, and common across their native ranges.
Interesting Facts
Broad-faced sac spiders are exceptional climbers and can easily scale smooth vertical glass surfaces thanks to specialized claw tufts on their feet.
Photography Tips
Use macro lenses with good lighting to capture the texture and color contrast of the dark cephalothorax against the abdomen. Photograph from above while the spider is resting on a flat surface.
Identified: 2026-08-24T13:36:00.780619