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Written by: Diana Drips

Published: 13 October 2024

For many, the autumnal equinox brings a sense of hope and the promise of relief from the heat. For others, it is a reminder that the spooky season is inching closer, one cobweb at a time.

As the days shorten and the weather cools, we will indeed begin to see more spiders in their webs, and one spider takes center stage when it comes to the spooky: the infamous Western black widow.

They are one of the most feared spider species and one of the most misunderstood.

You have no doubt heard horror stories about them lurking in garages and woodpiles, waiting for an opportunity to jump out and bite you.

Very spooky indeed, but spoiler alert, they can’t jump, and they only bite under very specific circumstances. More on this later.

While I love a scary story at Halloween, I think this villain deserves a bit of a rebrand. So, allow me to reintroduce you to one of our fascinating and misunderstood neighbors.

The Western black widow, Latrodectus hesperus, is a species of spider native to western North America and is one of 32 known species of Latrodectus spiders worldwide.

Females are identifiable by their shiny black exoskeleton, bulbous abdomen and red hourglass on their underside, growing up to 1.5 inches in length.

In contrast, males are light brown or gray with white and orange markings and are only about half the size of females.

Female black widows can live up to three years, but a typical lifespan is one year. Males, in contrast, live only one to two months after reaching adulthood.

Females will not venture more than a foot or two from their web during their lifetime. This makes for interesting nature watching; if you know where one lives, you can pretty much be guaranteed to find her again tomorrow evening and the evening after that. If she survives the winter, she will come out in the same spot in spring.

They make their irregular, messy webs about 1 to 2 feet off the ground, and unlike spiders that make new webs daily, Latrodectus hesperus works on the same web throughout their lives, often eating damaged parts of the web to reuse the silk. During web maintenance we can really see their beauty, as they seem to dance, pirouetting upside down as they strengthen their web.

Being primarily nocturnal, they have very poor vision, using their eyes to sense motion and light. They are, however, highly perceptive to the slightest movement and have tiny cracks called slit sensilla on their legs that allow them to sense movement and soundwaves, prompting scientists to compare their legs to ears. Fascinatingly, spiders’ webs have been theorized to be a sort of external mind, an extension of the spider’s sensory experience.

You may have heard the distinct crackling sound of a black widow web being broken, a sign of the unique strength of their silk among spiders. Their silk is stronger than steel by weight. Highly effective predators, they use their powerful web to capture insects like mosquitoes, flies, wasps, cicadas and even cockroaches, helping to keep our ecosystem in balance.

While they are fierce predators, they are otherwise quite docile. For spiders, it is nearly always better to flee rather than fight when faced with a threat. Their telltale red hourglass is meant as a silent warning to potential predators to keep our distance. Venom is metabolically expensive, a precious resource used to immobilize prey, it is rarely used for defense.

Researchers Nelsen, Kelln and Hayes conducted a study in 2013 at the University of Loma Linda in which Western black widows exhibited decision making about resource use when assessing a threat, choosing to use venom only when deemed absolutely necessary.

In the study, 43 Western black widow spiders were “poked” and “pinched” using artificial fingers to assess frequency of biting behavior when threatened. The findings: not a single spider bit after one poke by an artificial finger, instead fleeing or moving away from the threat.

Surprisingly, none of them bit even after 60 repeated pokes! It was only after being pinched between two fingers that 60% of the spiders did bite, but of those bites only 50% contained venom.

A bite without venom, or a “dry bite,” is meant to cause initial pain and deter the threat, and while painful, it does not pose a health risk. (Do not try this at home!)

According to Merri Lynn Casem, professor and spider researcher at Cal State Fullerton, the symptoms resulting from a venom-containing bite are caused by the protein alpha latrotoxin. Symptoms can include nausea, vomiting, pain and abnormal heart rate.

Modern treatments for bites focus primarily on pain relief. An antivenom can be used in severe cases. In cases where serious symptoms occur, it is usually due to an allergy, rather than the venom itself. The reality is that humans rarely die from a black widow bite. In fact, the last documented case of a death by a black widow bite in the US was in 1983.

Female black widows also have the reputation of being the femme fatale; the story goes that they habitually feast on males after mating.

The truth is that most male black widows live to mate again. In fact, according to natural history scientists at Seattle’s Burke Museum, there has never been an observed incident of a Latrodectus hesperus female eating a male after mating outside of captivity. There are other species of widow spiders that do habitually eat their mates, but in this species, the namesake is largely a myth based on behavior in captivity.

Males identify themselves with pheromones and with a specific set of movements as they enter the web of a potential mate to avoid being mistaken for prey. Males are known to occupy and guard the webs of females from other males, sometimes tearing down sections of her web to deter other males, a behavior called “web reduction.” Once mating has occurred, he then leaves her web, most often unscathed and in search of another mate.

Latrodectus hesperus are protective mothers. They are more prone to bite when their egg sac is threatened.

The abdomen of a gravid (pregnant) widow swells before her eggs are laid. Those big widows you have seen are not more fearsome, they are simply pregnant. In spring and summer, they lay tiny pink eggs and spin a protective silk egg sac.

They can have multiple egg sacs in a year, each containing hundreds of eggs, but only one to 12 of the hatchlings from a sac survive longer than 30 days.

Like many tall tales told around Halloween, the truth is much less spooky when we learn the details.

I hope that when you see a beautiful Western black widow this fall, that you think twice about squishing her, and that you maybe even compliment her on her fabulous dance moves and thank her for keeping our fly numbers in check.

Diana Drips is a Certified California Naturalist. Tuleyome is a 501(c)(3) nonprofit conservation organization based in Woodland, California. For more information go to www.tuleyome.org.