Western Black Widow
Latrodectus hesperus
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, often bulbous abdomen, comb-like serrated bristles on the tarsus of the fourth pair of legs used to pull silk from the spinnerets, and untidy, irregular tangle webs.
Physical Description
The spider has a compact, glossy appearance with a distinct globose (spherical) abdomen and a smaller cephalothorax. Females are significantly larger than males, featuring a very prominent, bulbous abdomen. The surface is smooth with fine hairs.
Size Estimate
Body length for the adult female is approximately 8 to 13 millimeters, with a leg span reaching up to 38 millimeters. This specimen appears to be an adult or subadult female based on the abdominal proportions.
Coloration & Markings
Glossy jet black base coloration. While typical western black widows often feature a red or orange hourglass marking on the ventral side of the abdomen, some individuals may have spots or dorsal red markings, or can be entirely black depending on maturity and specific regional variants.
Web Type
Irregular, three-dimensional tangle web or cobweb constructed close to the ground in dark, undisturbed areas. The web features a sticky, scaffolding-like structure with a funnel-like retreat where the spider hides.
Eye Arrangement
Eight small eyes arranged in two transverse rows of four, typical of the theridiid family, with lateral eyes generally touching or closely paired and median eyes forming a trapezoid.
Leg Characteristics
Long, slender, smooth legs without prominent spines, uniformly colored black to match the body. They maintain a sprawling posture in the web and use specialized serrated setae on the hind legs to manipulate silk.
Venom & Safety Information
Venom Information
Contains latrotoxin, a potent neurotoxin that affects the nervous system by causing massive neurotransmitter release. Potent relative to humans, though rarely fatal with modern medical care.
Medical Significance
Medically significant. A bite can cause severe local pain followed by painful muscle cramps, abdominal rigidity, sweating, nausea, and tremors. Seek medical attention promptly if bitten, though symptoms are treatable with antivenom and muscle relaxants.
Safety Recommendations
Wear gloves when moving woodpiles, rocks, or stored items in dark areas. Inspect shoes and clothing left outside. If found indoors, relocate safely using a container and a piece of card, or contact pest control if infestations are severe.
Habitat & Behavior
Habitat & Range
Found throughout western North America, including Arizona. Prefers dry, arid environments, under rocks, in rodent burrows, woodpiles, outbuildings, garages, and dark, undisturbed corners around human habitations.
Behavior & Temperament
Reclusive, non-aggressive, and nocturnal. They typically retreat when disturbed and only bite defensively when trapped, squeezed, or accidentally pressed against human skin.
Diet & Prey
Primarily feeds on crawling and flying insects such as beetles, flies, grasshoppers, and ants. Prey stumbling into the sticky lower scaffolding of the web is quickly subdued by being wrapped in viscous silk and envenomated.
Seasonal Activity
Active year-round in warmer climates like Arizona, with peak activity and mating occurring during the warm summer months. They overwinter in sheltered locations as adults or subadults.
Description
The Western Black Widow is one of North America's most recognizable spiders due to its glossy black body and infamous reputation. Thriving in the arid climates of the American West, this reclusive cobweb weaver plays an important role in controlling insect populations. While medically significant, they are entirely non-aggressive and prefer to flee or play dead rather than bite.
Key Features
Glossy black, globose abdomen; slender legs; construction of an irregular, sticky cobweb in dark recesses; presence of a red ventral hourglass marking in most mature females.
Similar Species
False black widows (Steatoda grossa) which lack the red hourglass and have a more oval, less glossy abdomen; male or juvenile black widows which may feature lighter banding and red/white dorsal spots.
Life Cycle
Females produce pear-shaped papery egg sacs containing hundreds of eggs. Spiderlings disperse via ballooning after hatching. Females can live up to several years, while males have much shorter lifespans and often fall victim to sexual cannibalism.
Ecological Importance
Serves as an effective natural predator of pest insects, helping to control populations of beetles, roaches, and other arthropods in both natural and domestic environments.
Conservation Status
Not evaluated by the IUCN, but populations are secure, highly adaptable, and thriving across their native range.
Interesting Facts
Despite their fearsome reputation, black widows rarely inject venom in all defensive bites ('dry bites'). The female's venom is specifically adapted for invertebrate prey, but humans react strongly to the neurotoxins.
Photography Tips
Use macro lenses from a safe distance without touching the spider. Illuminate with diffused lighting to highlight the glossy texture of the cephalothorax and abdomen. Photograph the ventral side only if safely secured, as this shows the diagnostic hourglass.
User Notes
in Arizona
Identified: 2026-09-18T22:57:58.793488