Discover the Real Reason Why Black Widows Eat Their Mates

Most people fear black widows, and it’s for justifiable reasons. These members of the Theridiidae family can quickly land you in the hospital because of their venomous bites. But interestingly, they’re more notorious for something else — sexual cannibalism. Thanks to their grisly mating rituals, love can be fatal for these venomous spiders. This article uncovers the real reason black widows eat their mates. It will also explore some other habits of the black widow spider, so let’s get started!

Why Do Black Widows Eat Their Mates?

Female black widows sometimes eat their mates for nourishment, to declare their sexual partner preference, and leave their reproductive options open. Typically, the female members of the widow family are larger than the males, so they have the upper hand during copulation. In fact, research shows that the smaller the ratio between the female and male body length, the higher the chances of the former eating the latter. Thus, when a male black widow goes nosing around a female’s web during the mating season, there’s some likelihood it will die soon after, leaving its hungry mate with more than just sperm. At the same time, females tend to gobble down less desirable males before mating even occurs.

But here’s an even more intriguing fact. Some representatives of the black widow genus, like the Australian redback, have a penchant for the gruesome sex and actually sacrifice themselves during mating. As you might ask, what exactly is worth dying for? Well, fatherhood! By flipping into his partner’s fangs to allow her to devour him, the male redback has more time to fill his mate with more sperm and pass on his genes.

What about males eating females? It seems that the reasoning for this is similar. Hunger and a drive for the best reproductive options drive male black widows of certain species to devour “unsuitable” mates.

How Do Black Widows Find Mates?

When it comes to looking for sexual partners, male black widows are competitive, as a study published in 2019 shows. Instead of finding their own way, they leverage their competitors’ silk trails to locate potential mates, which saves them time. And even after they find them, the arachnids may have to fight other male black widows or rivals to pass on their genes. This battle royale for genetic preference is something seen in a variety of animals but none quite so strongly as the deadly mating dance of this fearsome spider.

Black Widow Spiderlings: Number of Eggs Per Egg Sac

One egg sac produced by a female black widow contains about 150-250 eggs. The spider may produce 5-10 egg sacs, and the eggs usually hatch after the incubation period (26-30 days). After the spiderlings emerge, they disperse to various areas, and like their mothers, they’re also cannibals. Therefore, if food is scarce, these arachnids munch on their siblings but remain harmless to humans.

This siblicide seems to help ensure that the strongest and more virile baby spiders reach adulthood and breeding. A similar siblicide happens in hyena families, where brutal siblicide and infanticide help to decide who will run the cackle in adulthood. In hyenas, this also helps maintain the social standings of adult members within the cackle. Is this true for spiders, too? Actually, no. Black widow spiders are incredibly solitary creatures who only become social during their brutal mating ritual. The culling of baby black widows in fits of siblicide is completely based on food scarcity.

More Interesting Facts About Black Widows

Besides the occasional sexual cannibalism, there are many other intriguing facts about black widows, including the following: 

Females Have Poor Vision

Unknown to many, female black widows have poor eyesight. These shy — yet somewhat dangerous — arachnids depend on vibrations transmitted through their webs to know what’s happening around them. That includes whether a prey, predator, or mate is close by. Generally, male black widows take advantage of this during the mating season. By destroying the female’s web, a male black widow makes it difficult for their potential mate to know the suitors nearby and send out a message that she’s ready for copulation. After limiting the number of prospective partners (and rivals) available, the male approaches the female to have sex.

They Are Not the Deadliest Spiders

Rumor has it that black widows are the planet’s deadliest spiders. But that’s untrue! The world’s most dangerous spider is the Sydney funnel-web spider because its venom can kill you within 15 minutes following the arachnid’s bite. The latter triggers a series of symptoms, which include abdominal pain, nausea, numbness and swelling, and breathing difficulty. While a black widow’s bite may cause some of these complications, it’s unlikely to kill you. Besides, you can easily find antivenom for treatment.

Not All Black Widows Are Black

When most people talk about black widows, they presume all these spiders are black. But on the contrary, they’re not. As of this writing, we have over 30 known black widow species, including the western black widow (Latrodectus Hesperus), the redback spider (Latrodectus hasselti), and the southern black widow (Latrodectus mantans). While some of these arachnids are black, others, like the males, are gray or brown with small red marks.

Sexual Cannibalism in Black Widows

In the widow family, sexual cannibalism is somewhat common. The name ‘black widow’ is even derived from the belief that the females eat their mates after sex. However, this is not what all black widows do and the mythology about the sexual cannibalism in their species is much overblown. In a 2013 NBC article, new editor Megan Gannon quotes research that may debunk the mythology.

A team of researchers at Masaryk University – located in the Czech Republic – more deeply studied the habits of black widow spiders. One tactic they used was to make sure all of the spiders had plenty to eat. Some research suggests that female black widows only devour their mates when they are hungry. In this study, the researchers actually found plenty of evidence of reverse cannibalism – the males eating the females. In fact, it seems some species of black widow spiders breed based on the selection of the male. This species, Micaria sociabilis, showed a higher rate of males selecting their mates and cannibalizing unworthy female spiders. It seems that the males selected mates based on the age of the female spider.

Further, researchers disproved voracity in females hunting prey causing a “spillover effect” in breeding in an academic study published in 2021 by Rok Golobinek, Matjaž Gregorič, and Simona Kralj-Fišer. The researchers in this study are from the Jovan Hadži Institute of Biology and their study was conducted on the Mediterranean black widow (Latrodectus tredecimguttatus). The study found that male and female black widows have consistent individual differences in aggressive behaviors that do not correlate to the individual size of the spider. However, this study also confirmed that differences in body size between the copulating male and female distinctly correlated to the act of cannibalism. Basically, a small female black widow may still cannibalism a male black widow if he is distinctly smaller than her. Inversely, a larger male breeding with a smaller female increased the chances of the male cannibalizing the female. In short, size does matter for black widow spiders.

Where do Black Widows Live?

Black widow spiders live in every state in the United States except for Alaska. However, they prefer warmer southern climates and live more abundantly in desert regions such as the Sonoran and Mojave deserts. States with higher black widow populations include Texas, Oklahoma, and Kansas.

Black widows like to nest near wood piles and in rodent holes, basements, barns, and unused clothing and blankets. They have a preference for warm, dark, and dry environments. They’re quite reclusive and solitary spiders, so they definitely prefer areas that get very little traffic, noise, or light. Spaces like this also include garages and areas full of unused clutter.

Summary

Black widow spiders of any species do not consume their mates at as high a rate as we have been led to believe. In fact, several breedings between widow pairs do not result in death. Sexual cannibalism is not uncommon, though, and it seems to be based on hunger and viable mate selection. Both male and female black widows cannibalize one another, though females do so at a much higher rate. In addition, baby black widows will often eat each other if there is food scarcity. These solitary spiders seem completely driven by an instinctual desire to survive and will go to great lengths to do so.

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