Northern Yellow Sac Spider, Mild's Sac Spider
Cheiracanthium mildei
Cheiracanthiidae (Yellow Sac Spiders), Order Araneae
Physical Description
Small, slender-bodied spider with an elongated oval abdomen and a distinct light brown to translucent prosoma. The body surface is smooth to lightly velvety with fine short hairs.
Size Estimate
Body length is approximately 5-10 mm; total leg span ranges from 15-25 mm. The pictured specimen appears to be an adult or subadult female.
Coloration & Markings
Pale yellow, pale greenish-tan, or cream color overall. The dark brownish tip of the chelicerae (tarsal claws/fangs) and a slightly darker faint cardiac stripe on the anterior dorsal abdomen are typical key traits.
Web Type
Does not build prey-capture webs. Instead, it constructs a small, flattened, tubular silk sac in hidden crevices or leaf folds for resting during the day.
Eye Arrangement
Eight small eyes arranged in two horizontal rows of four across the front of the carapace, with the anterior median eyes typically dark and posterior eyes somewhat reflective.
Leg Characteristics
Long, thin, translucent yellow legs; the first pair of legs is noticeably longer than the rest. Legs feature small dark claws at the tips and fine hairs.
Venom & Safety Information
Venom Information
Contains mild cytotoxic and neurotoxic components. Envenomation causes localized pain similar to a bee sting, slight swelling, and redness.
Medical Significance
Not considered medically significant. Historical claims linking yellow sac spider bites to necrotic arachnidism have been largely disproven by modern medical research.
Safety Recommendations
If found indoors, safely capture using the cup-and-paper technique and release outside. Avoid pressing against skin. Wash bites with soap and water and apply a cold compress if bitten.
Habitat & Behavior
Habitat & Range
Native to Europe, North Africa, and the Middle East, but now widespread across North America. Frequently found inside homes, on walls, ceilings, around window frames, and outdoors on foliage.
Behavior & Temperament
Active nocturnal hunter that wanders freely at night searching for small insects. Fast-moving and shy; generally non-aggressive towards humans unless trapped or squeezed.
Diet & Prey
Small invertebrates including flies, moths, leafhoppers, ants, scale insects, and other small spiders.
Seasonal Activity
Most active outdoors during late spring through summer. Indoors, they are commonly sighted late summer through autumn as mature adults seek shelter and mates.
Description
The Northern Yellow Sac Spider is a small, pale nocturnal wandering spider often encountered indoors during cooler autumn months as it seeks shelter.
Key Features
Pale yellow to cream translucent body, elongated abdomen, dark chelicerae tips, longer first pair of legs, and absence of dark abdominal spots or contrasting bands.
Similar Species
Cheiracanthium inclusum (Black-footed Yellow Sac Spider, has darker leg tips), Clubiona species (Sac Spiders, broader head region), Hibana gracilis (Ghost Spider, has double faint stripes on carapace).
Life Cycle
Females lay eggs inside a dense silk sac during summer and actively guard them until spiderlings hatch. Lifespan is generally around 1 to 2 years.
Ecological Importance
Serves as an effective natural pest controller in garden habitats, agricultural fields, and indoor environments by consuming nuisance flies, agricultural pests, and mosquitoes.
Conservation Status
Not evaluated by the IUCN. Abundant and widespread with stable populations; considered an introduced synanthropic species in North America.
Interesting Facts
Yellow sac spiders are notorious for being attracted to the smell of gasoline vapor and have historically caused clogged fuel lines in stored vehicles.
Photography Tips
Focus on capturing the front of the spider showing the chelicerae, leg lengths, and abdominal shape. Good top-down or direct head-on lighting helps show eye pattern and translucent body color.
Identified: 2026-07-23T16:27:17.868638