Male black widow spiders are pickup artist masters: webs, pheromones, communication.

Black Widows Could Teach Pickup Artists How to Up Their Game

Black Widows Could Teach Pickup Artists How to Up Their Game

Wild Things
Slate’s animal blog.
July 24 2015 3:04 PM

Black Widows’ Bizarre Mating Rituals

A male black widow reduces a female's web.
A male black widow reduces a female's web.

Photo by Sean McCann/www.ibycter.com

Pickup artists, those supposed masters of seduction, could learn a few tricks from the male black widow spider: Target single virgins. Communicate that you’re interested. Help yourself to any snacks she has lying around. And—most importantly—tear apart her home, fashion the broken pieces into a bundle, and wrap the bundle in silk secreted from your butt (sorry, your spinnerets).

Sounds sexy, doesn’t it? How could she possibly resist? But given that black widow females are famous for devouring their mates even after a good date, I have to ask: Why do the puny males dare destroy the webs of the large, carnivorous females?

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Arachnologists from Simon Fraser University in British Columbia, Canana, have figured out why Western black widows—a venomous but shy species—use destruction for seduction. Their discovery deciphers a little-studied form of spider communication that might someday help protect people.  

The story starts on the shores of Island View Beach in British Columbia, where people stroll with their dogs past beached logs infested with hundreds of hungry, horny black widows. It’s a beach that would’ve been a nightmare for the study’s lead author, back when she was a little kid.

"I used to be terrified of spiders,” says Catherine Scott, who is starting her doctoral work at the University of Toronto. But when she started learning about spiders in college, “I immediately fell in love them with them.” As a self-described spider fanatic, Scott knew that spiders put human Romeos to shame: Male wolf spiders “purr” to romance females. Male redback spiders feed themselves to their mates. And when given the chance, male Western black widows tear up webs built by females—although no one ever figured out why.

To study why the males engage in “web reduction,” Scott and her colleagues first needed a lot of spiders. They caught 50 “really, really fat” pregnant females on Island View, says Scott, and raised their babies in the laboratory. I know—this sounds absurdly dangerous. But Scott says that while “you have to be careful and respect them,” because the spiders do have dangerous venom that requires treatment with antivenom, they don’t usually kill people. The very young and very old are most likely to die from the spiders’ bites. Plus, black widows don’t bite unless they’re being squished, say, in the toe of an old boot where they built a web.

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Once the researchers had a lot of spiders, they needed a lot of web. They gave 60 grownup females wire-mesh cages and let each one build a fine web home over a week. Webs are terribly important for the females: The webs snare her prey, cloak her from predators, and even function as a homemade Match.com.

When a female is ready to mate, she coats her web with pheromones that act like a “chemical personal ad,” says Scott. These scents broadcast the female’s age and virginity. The virginity is important not because the males are into promise rings but because black widows have “first male sperm precedence,” says evolutionary biologist Paula Cushing, curator of invertebrate zoology at the Denver Museum of Nature & Science. This means that the first male to mate gets to fertilize most of a female’s eggs. Along with her virginity and maturity, the female broadcasts how hungry she is. Even though sexual cannibalism is rare, males are still at some risk anytime they approach a much larger female, and they want reassurance that she is starving just for a roll in the web.

After allowing a week of web-building, Scott took out the females and divided the cages into three groups. For the first, she left the web intact. For the second, she put a male black widow inside and let him reduce the web, tearing and bundling it until about 50 percent of the original web was gone. And for the third, Scott mimicked the male spiders by snipping away half of each web with scissors. Along with a control group (empty cages with no web), Scott turned these cages into traps for lusty male spiders by lining them with sticky tape. Then she set her traps along Island View Beach at sunset, just before nocturnal black widows get active.

"The males came out of the woodwork,” says Scott, as soon as they smelled the webs of all those “fresh, virgin females.” Within 24 hours, the arachnologists trapped 230 hopeful males. Except for 6 males that blundered into the web-free traps that had never housed a female, most males were trapped by the cages with webs. The intact webs covered in pheromones were clearly the sexiest, nabbing 105 unfortunate males. The webs that Scott had destroyed caught 82 males—suggesting that a little less pheromone-drenched web was a little less sexy. The least sexy were the webs reduced by other males: Only 34 males were still interested—barely one third the number who went for the intact webs.

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There was something special about how the males reduced webs, Scott realized. “Whatever they’re doing is more effective” than a human trimming away half. One possible reason is that the females might concentrate their pheromones in only a few areas, which the males specifically destroy. Another possibility is that when the males bundle web into their own silk, they’re sealing off the female pheromones. And when he’s bundling up her pheromones, he might also add his own—the chemical equivalent, Scott says, of shouting, “don’t bother, I’m already here."

But why, under any circumstance, do the females let the males reduce the webs they need to eat and survive?

The females might actually appreciate having their pheromone-drenched webs destroyed. “Once she’s mated,” Scott says, the “females don’t produce attractive pheromones anymore.” She only needs one male to fertilize her eggs; extra males are just backups. “If she doesn’t want to mate, she’ll have to chase them off the web,” says Scott—and chasing uses up time and energy she could spend tending her egg sacs. By destroying the web, the male lessens the chance he’ll have competition and gives the female room to build a new web that doesn’t have the same attractive pheromones.

But the female’s sex life isn’t over once she’s a mom. If she wants to mate some more, she douses her new web with another chemical personal ad—and more males will come.

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Repurposing this response to pheromones might help protect people, says Scott. Black widows can be a danger to grape pickers when they nest in vineyards. By understanding the pheromones that make up chemical personal ads, Scott says that exterminators might be able to develop traps that lure male spiders with pheromones, which could be an effective, nonpesticide approach to controlling black widows.

But destroying her beloved spiders isn’t Scott’s goal. “Really, it’s just super cool” how spiders communicate, says Scott. There’s plenty more to understand, and Scott wants to figure out if the males really are dousing the female webs with “don’t bother” pheromone.

If they really are, perhaps the best advice for pickup artists is this: Once you’ve found your single virgin, eat all her potato chips. Burn down her home. And—most importantly—douse the smoking ashes with Axe Anarchy for Him Daily Fragrance.

But just be ready to run if she gets hungry.