Surviving sex with black widows

August 8, 2011 By Larry O'Hanlon
A black widow spider couple clings to a web. Recent research shows that males of the species seek out recently-fed females for mating. Credit: J. Chadwick Johnson

Scientists have discovered that male black widow spiders, famous for ending up as their mates' post-coital supper, are not as clueless as you might think. In a series of careful experiments, a team of researchers from Arizona State University West in Glendale has teased out evidence that black widow males do their best to avoid getting eaten by choosing mates who have recently fed.

The work also details something else very rare in the animal kingdom: a sexual power struggle in which males have the upper hand.

"Most of the time people focus on " when it comes to the power of selecting mates, said spider researcher Eileen Hebets at the University of Nebraska in Lincoln. That power is critical to adaptation and evolution, and ultimately shapes the species. "It's much less common to think of males as a potential source of selection," she said.

It's only in extreme situations -- where mating brings the risk of death, for example -- that male selection appears and can be studied.

In the case of the North American , Latrodectus hesperus, the Arizona experiments reveal that male black widows can detect telltale on the webs of females. They can smell which females are well-fed and which are hungry, which leads to a simple choice: Which one is less likely to eat them? This ability to sense well-fed females also has another advantage: by choosing plump females, males are also choosing mates that are likely to produce large numbers of eggs.

"It's a ," said Chad Johnson, the lead investigator on the study, which was published in the August issue of the journal Animal Behavior .

In most , females dictate the course of reproduction, said Johnson. They work hard to produce and safeguard a few eggs, while males generate lots of sperm at little personal cost. That difference in "investment" usually leads males to be promiscuous while females are choosy. But in species like the black widow, the danger of mating is so great for the males that they have to be the choosy ones.

To check this idea, the Arizona team put their laboratory-raised black widows through four experiments. First, they tested whether males were more likely to engage in courting behavior on the webs of well-fed females more than on the webs of hungry females -- even in the absence of the females themselves. The lab spiders did exactly that.

In their second experiment, the researchers put the females back into the mix. Again, the males greatly preferred the plump females.

Next, the team pulled a confusing switcheroo on the males by putting well-fed females on the webs of starved females and starved females on the webs of well-fed females. For the most part, the males' behavior reflected this confusion by showing no significant preference for the well-fed females that were placed on the wrong webs.

Finally, the researchers rolled up onto sticks webs from females that were either well-fed or starving and presented them to males to find out if it was a chemical or structural difference in the web that was cluing in the males. Once again, the males preferred the webs of well-fed females, supporting the idea that the clue is some unknown chemical in the webs that the males can smell.

"He's not at all complicit in his own demise," said Johnson of the black widow males. "He's making the best of a bad situation."

Despite their efforts, though, male black widows frequently don't survive mating. Although the rates of survival were not the focus of this study, in some other widow species the risk of getting eaten is much greater.

"There is almost a continuum with spiders of varying degrees of risk," said Hebets. This is exactly what makes them so fascinating to study, she added.

There are even some species where males can get eaten before mating. "That’s obviously an even more extreme freak show," said Johnson.

Explore further: Male black widows look for well-fed mates

More information: Animal Behaviour, Volume 82, Issue 2, August 2011, Pages 383-390. doi:10.1016/j.anbehav.2011.05.018

Related Stories

Male black widows look for well-fed mates

July 7, 2011

( -- According to a new study published in Animal Behaviour, a male black widow spider is able to identify a female spider that has eaten well by simply taking a few steps on the web she spins. Finding a well-fed ...

In spiders, size matters: Small males are more often meals

September 10, 2008

Female spiders are voracious predators and consume a wide range of prey, which sometimes includes their mates. A number of hypotheses have been proposed for why females eat males before or after mating. Researchers Shawn ...

Mating that causes injuries

February 20, 2009

Researchers at Uppsala University can now show that what is good for one sex is not always good for the other sex. In fact, evolutionary conflicts between the two sexes cause characteristics and behaviors that are downright ...

Choosy females make colourful males

May 9, 2006

Female fish prefer brightly coloured males because they are easier to see and are in better shape concludes Dutch researcher Martine Maan following her study of fish speciation in the East African Lakes. Environmental variation ...

Recommended for you

Even wild mammals have regional dialects

December 13, 2017

Researchers from Cardiff University's Otter Project have discovered that genetically distinct populations of wild otters from across the UK have their own regional odours for communicating vital information to each other. ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 08, 2011
An article that encourages wry smiles. Yes. Of course. No other perspective than the human perspective is accessible for animal behavior observation. Observational data remains unhampered by interpretation. And interpretation relies on consistency.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.