Living with Black Widows in the Garden

Black widows are among the most common garden spiders, and despite their fearsome reputation, they're largely beneficial. Here's an introduction to these infamous arachnids, along with personal encounters and practical insights.

Early Encounters

My first memory is from childhood in northern New Mexico: a 10-foot-deep concrete pit filled with dense white webs and hundreds of half-inch egg sacs—black widow nurseries. My father said over 100 spiders lived there, fueling nightmares for years. Since then, nearly every home I've had has hosted thriving populations. I've seen thousands yet never been bitten.

Coexisting as a Gardener

As an avid gardener in Southern California, I've had to make peace with them. Hundreds inhabit my small garden—under rocks, in pots, behind bricks. They're year-round residents, outlasting seasonal insects. The western black widow (Latrodectus hesperus) is our local species. Their venom is 15 times more potent than a rattlesnake's, but bites have only a 1% mortality rate; healthy adults recover in a week. Children and the elderly face higher risks, but deaths are rare. These spiders are non-aggressive and flee when disturbed. Bites typically occur only if a spider is pressed against skin or trapped in clothing.

Northern (L. variolus), Southern (L. mactans), and Western (L. hesperus) black widows.

Close Calls and Pet Safety

Once in college, a fat black spider crawled up my pant leg during a field trip. Frantic jumping and slapping ensued—no bite, just a squashed specimen (which my instructor rejected because arachnids aren't insects). Pets rarely get bitten due to fur and tiny fangs; in 22 years as a veterinarian, I've never diagnosed a black widow bite in an animal.

Tiny pets like this Chihuahua could be at risk, but actual bites are extremely unlikely.

Biology and Behavior

Only the shiny black females with the red hourglass are dangerous. Males are smaller, lighter, lack the hourglass, and are harmless. Webs are messy, irregular, rarely spanning more than 18 inches, often in dark corners. Females produce 4–8 egg sacs in a lifetime, each with up to 400 eggs. They live 8–14 months; males live less. Despite high reproductive potential, only ~1% of spiderlings survive to first molt due to cannibalism and predation. Females are nocturnal, most visible at dawn and dusk.

Immature black widow.

The name "widow" comes from sexual cannibalism, though it doesn't always happen. I've never witnessed it, but I've seen praying mantises do it frequently.

Beneficial Predators?

Black widows eat moths, flies, and other flying insects. In my garden, major pests are grasshoppers, aloe mites, mealybugs, scale, slugs, and snails—none typical widow prey. Their actual pest-control value is debatable, but they're here to stay, so I've learned to tolerate them.

Rare catches: a grasshopper and a slug (the slug was eventually dropped).

^[1] National Geographic