Planet Earth

Male Black Widow Spiders Try to Avoid Sex That Will Kill Them

DiscoblogBy Joseph CastroJul 6, 2011 8:17 PM

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Sometimes sex just isn’t worth your life. For male black widow spiders

, standing at just a quarter of the size of their mates, sex involves a very real danger: females of the species have no qualms about turning cannibalistic if they’re hungry after getting down and dirty. But it seems that it’s more than just a game of chance for horny male spiders. Researchers at Arizona State University have now learned

that simply walking on the webs of female spiders can provide males with chemical cues telling them if their potential mates are ravenous enough to eat them. In the study published in the journal Animal Behavior

, researchers routinely fed one group of female spiders for several weeks while starving another group (noticeably shrinking their sizes). They then looked at the courtship behavior of the male spiders in a series of tests. In the first experiment, the researchers placed the males on the females’ webs while the cannibals were absent. Here, the males were far more likely to begin their courtship rituals on the webs of cricket-full females. A male’s courtship dance, the researchers explained, lasts an hour or two and involves tapping different areas of the web. "It's like spider tai chi; by waving his legs and plucking, he's providing vibrations that are very distinct to tell the female, 'I am not a prey item,’” lead author James Chadwick Johnson told BBC Nature

. To make sure that the males were only picking up cues from the silk—and not taking the obvious hints from the dead bodies scattered about—the researchers presented the male spiders with web-wrapped toothpicks cleaned of any leftover food. Again, the males liked the silk of satiated females. In other tests, the males reacted similarly when the females were present; and in a final experiment, the researchers tried to trick the male spiders by mismatching the females and their webs (well-fed females on the webs of starving females and vice versa). It didn’t work most of the time—males chose the fattened females, suggesting that males pick up stronger chemical cues from the actual spiders than from their webs. It’s important to note that while the male black widow spiders preferred the well-fed females, they didn’t shun the hungry spiders altogether, though they’re probably regretting it now in spider heaven. Five out of seven starved females attacked their mates after sex, with three of the females successfully killing their foolish mates. Comparatively, none of the satisfied females attacked their mates. But one still has to wonder: Are the males really valuing their lives, or do they just prefer their lady-spiders nice and plump? (via BBC Nature

)

Image: Flickr/laurence_grayson

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