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 small, somewhat flattened cephalothorax. The exoskeleton has a high-gloss, lacquer-like appearance. Females are significantly larger than males, with thick, smooth-textured bodies.
Size Estimate
Body length 8–15 mm (females); leg span approximately 25–40 mm. This specimen appears to be an adult female.
Coloration & Markings
Jet black across the entire body. While the ventral (underside) hourglass marking is not visible in this photo, mature females are typically solid black on the dorsal side. Juveniles and males may have white, red, or tan streaks on the back.
Web Type
Tangle web or cobweb. These are irregular, three-dimensional structures of exceptionally strong, non-sticky silk that crackle like parchment when torn. Webs are typically built in dark, low-disturbed areas.
Eye Arrangement
Eight eyes arranged in two rows of four. The eyes are small and typically not visible without extreme magnification, as they blend into the dark cephalothorax.
Leg Characteristics
Long, slender legs. The first pair is typically the longest. A 'comb-foot' (row of serrated bristles) on the fourth tarsus is used to wrap prey in silk. The legs are typically jet black like the body.
Venom & Safety Information
Venom Information
Neurotoxic venom containing alpha-latrotoxin. It is highly potent but delivered in very small quantities. It affects the nervous system, causing massive release of neurotransmitters.
Medical Significance
Medically significant. Bites cause 'latrodectism,' characterized by localized pain, muscle cramping (especially in the abdomen and back), nausea, and sweating. While rarely fatal to healthy adults, medical consultation is advised, especially for children or the elderly.
Safety Recommendations
Wear gloves when reaching into crawlspaces or handling insulation. If a spider must be moved, use a jar and stiff paper. Do not handle with bare hands. Seek medical attention if a bite is suspected.
Habitat & Behavior
Habitat & Range
Common throughout Western North America from Canada to Mexico. They prefer dark, undisturbed microhabitats such as crawlspaces, under porches, in woodpiles, and inside insulation as seen here.
Behavior & Temperament
A shy, nocturnal ambush hunter. They are not naturally aggressive and usually retreat to a corner of their web or 'play dead' when disturbed. Bites only occur if the spider is pinched or pressed against skin.
Diet & Prey
Primarily insects (beetles, crickets, flies) and other arachnids. They use 'gumfoot' lines to snag terrestrial insects, then quickly wrap them in extremely strong silk.
Seasonal Activity
Most active in late summer and autumn when females reach full size and egg sacs are produced. They may overwinter in protected areas like insulation.
Description
The Western Black Widow is an iconic and often misunderstood spider. Recognizable by its glossy black finish and bulbous abdomen, it is a master of pest control, though its proximity to human dwellings requires caution. It thrives in the dark, dry environments provided by home foundations.
Key Features
Glossy black globose abdomen, irregular high-strength tangle web, and the classic (though here hidden) red hourglass on the underside.
Similar Species
Steatoda grossa (False Black Widow) which lacks the red hourglass and has a more purple-brown tint; other Latrodectus species like L. variolus (Northern Black Widow).
Life Cycle
Females produce papery, tan, pear-shaped egg sacs containing 200-400 eggs. Spiderlings disperse via ballooning. Females can live up to 3 years in the wild; males have much shorter lives.
Ecological Importance
Highly beneficial as a natural pest controller, consuming large quantities of cockroaches, crickets, and beetles that occupy crawlspaces and gardens.
Conservation Status
Not evaluated by IUCN; populations are stable and widespread, often benefiting from human-modified environments.
Interesting Facts
The silk of a black widow is one of the strongest biological materials known, possessing a tensile strength comparable to high-grade steel. Sexual cannibalism is less common in L. hesperus than in its cousins.
Photography Tips
A ventral (underside) shot is best to confirm the hourglass marking. Use a macro lens or phone zoom with a flashlight positioned at an angle to capture the glossy texture without glare.
User Notes
Found in insulation under house
Identified: 2026-06-02T20:04:04.016656