Widow Spiders

Pronunciation

How to pronounce Latrodectus: /ˌlætrəˈdɛktəs/

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Summary

The genus Latrodectus, known as widow spiders, includes species such as the black widow and brown widow. These spiders are notable for their potent venom and distinct hourglass markings, especially in females. They are found worldwide except in Antarctica and thrive in dark, undisturbed habitats, often adapting to human environments. While they can pose health risks due to their bites, fatalities are extremely rare.

Physical Characteristics

Widow spiders (Latrodectus spp.) exhibit dimorphism between sexes; females are typically dark brown or shiny black, measuring 13 mm (0.51 inch) in body length (not including legs) and displaying an hourglass marking on the abdomen. Males are about half the size of females, displaying various red or white markings on their dorsal surface. They possess a distinct comb foot with a row of strong, curved bristles on the hind pair of legs, utilized in silk manipulation.

Identification Tips

Species identification can often be made based on location, hourglass markings on the abdomen, and general coloration. Female hourglass patterns vary: L. mactans and L. hesperus typically have complete hourglasses, L. variolus may have split or partial hourglasses, and L. bishopi often has absent or partial markings.

Habitat

Latrodectus spiders prefer dark, undisturbed locations such as under rocks, logs, in woodpiles, or within crevices and holes in dirt embankments. They build tangled, three-dimensional webs close to the ground or in corners of structures, adapting to human environments.

Distribution

Widow spiders are found on every continent except Antarctica. In North America, they are found widely across the southern and western United States, parts of Canada (especially Okanagan Valley), and some regions of Mexico.

Diet

Widow spiders mostly prey on small insects like flies, mosquitoes, and caterpillars, using their sticky webs to ensnare and immobilize them before injecting venom and consuming their liquefied remains.

Life Cycle

Black widow spiders mature in 2 to 4 months. Females mature within 90 days, living for about 180 days, and males mature in approximately 70 days, living only about a month longer. They can produce around 400 eggs in papery sacs, which incubate for 20-30 days.

Reproduction

Females can produce multiple egg sacs (up to 9) in a summer, each containing several hundred eggs. There are instances of sexual cannibalism where females may consume males after mating, though this is not a universal behavior across all species.

Predators

Main predators include mud-dauber wasps, particularly the blue mud dauber (Chalybion californicum), which primarily preys on black widow spiders.

Ecosystem Role

Widow spiders are significant predators in their ecosystems, helping control insect populations. They are also prey for certain wasps and other predators.

Cultural Significance

Latrodectus species have a notable place in cultural narratives due to their venomous bites and the myths surrounding their behavior, such as sexual cannibalism, enhancing their reputation as dangerous spiders.

Health Concerns

The bites of widow spiders can be dangerous, resulting in pain and systemic symptoms of latrodectism due to neurotoxic venom. However, fatalities are rare, and most bites are not severe. Males and juveniles do not pose significant risks to humans.

Collecting Methods

• Sweep nets
• Hand-collecting under logs and rocks
• Using pitfall traps

Preservation Methods

• Ethanol preservation
• Pinned specimens
• Frozen storage for DNA analysis

Evolution

The genus was first described in 1805 and has undergone several taxonomic revisions since then, including the placement of related species within broader classifications.

Similar Taxa

• Steatoda (false widow spiders)

Misconceptions

A common misconception is that female widow spiders always eat males after mating; while this occurs occasionally, it is not as frequent as believed. Male widow spiders do not present a medical concern to humans.

Tags

• Widow spiders
• Latrodectus
• Black widow
• Snake venom
• Arachnids