Western Black Widow
Latrodectus hesperus
Family Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
A medium-sized spider with a shiny, globose (bulbous) abdomen and a smaller cephalothorax. The exoskeleton has a high-gloss, porcelain-like finish. Females are significantly larger than males, which are more slender with longer legs and lighter coloration.
Size Estimate
Adult females typically have a body length of 14–16 mm (approx. 0.5 inches) with a leg span of up to 40 mm (1.5 inches). The specimen appears to be an adult female.
Coloration & Markings
Jet black overall. The most diagnostic marking is a bright red or orange-red hourglass shape on the ventral (underside) of the abdomen. Juveniles and males may have white or red stripes on the dorsal (upper) side.
Web Type
Tangle web or 'cobweb'. It is a messy-looking, three-dimensional structure made of exceptionally strong, non-sticky structural silk and sticky 'gumfooted' lines anchored to the ground.
Eye Arrangement
Eight eyes arranged in two rows of four. They are relatively small and provide poor image resolution, as the spider relies primarily on vibrations.
Leg Characteristics
Long, slender legs, with the first and fourth pairs being the longest. They lack conspicuous spines but have 'comb feet' (a row of serrated bristles) on the tarsi of the fourth legs to wrap prey in silk.
Venom & Safety Information
Venom Information
Contains alpha-latrotoxin, a potent neurotoxin that triggers a massive release of neurotransmitters. While very painful, it is rarely fatal to healthy adults with modern medical care.
Medical Significance
Medically significant. Symptoms include 'latrodectism'—intense local pain, muscle cramping (especially in the abdomen and back), nausea, and sweating. Seek medical attention if bitten, especially for children or the elderly.
Safety Recommendations
Wear gloves when moving firewood or cleaning out garages. If found on equipment, use a stick to gently relocate the spider to a distant area. Do not attempt to handle with bare hands.
Habitat & Behavior
Habitat & Range
Found throughout Western North America, from Western Canada to Mexico. They prefer dark, undisturbed microhabitats like woodpiles, garages, crawl spaces, and the undersides of outdoor equipment (like the grill pictured).
Behavior & Temperament
Generally shy and nocturnal. They are non-aggressive and typically retreat or play dead (thanatosis) when disturbed. Bites usually only occur if the spider is pinched or pressed against skin.
Diet & Prey
Primarily insects such as beetles, crickets, and flies, but capable of taking small lizards or other spiders. They use the 'flick-rag' technique to throw sticky silk onto prey before delivering a bite.
Seasonal Activity
Most active during late summer and autumn when females are fully grown and seeking mates or protecting egg sacs. They may overwinter in sheltered locations.
Description
The Western Black Widow is an iconic silhouette of the American West. Identifiable by its coal-black, lustrous body and red hourglass, it is a master of the messy cobweb. While feared, it is an introverted predator that provides excellent pest control.
Key Features
Glossy black globose abdomen; red hourglass on the underside; messy, high-strength tangle web; comb-like bristles on the hind legs.
Similar Species
Steatoda grossa (False Black Widow) which lacks the red hourglass and has a purplish-brown hue; Latrodectus mactans (Southern Black Widow) which is distinguished by geographical range.
Life Cycle
Females produce papery, tan, pear-shaped egg sacs containing up to 250 eggs. Spiderlings disperse via 'ballooning'. Females can live up to 3 years; males have significantly shorter lifespans.
Ecological Importance
Acts as an apex invertebrate predator in many microhabitats, significantly reducing populations of nuisance insects like cockroaches and agricultural pests.
Conservation Status
Not evaluated by IUCN; generally stable and common throughout its range. Not considered at risk.
Interesting Facts
The silk of a black widow is one of the strongest biological materials known. Contrary to the name, the female does not always eat the male; this behavior is more common in laboratory settings than in the wild.
Photography Tips
To safely document the hourglass, use a mirror placed under the web rather than getting close. Use a macro lens for detail and a diffused flash to manage the high-contrast highlights on the glossy body.
Identified: 2026-06-01T19:28:21.292590