Male black widows can pick up on chemical cues from female spiders and their webs about whether the females are hungry enough to devour the males post-coitus.
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.
What I didn’t realize is that there isn’t an impulse beyond simple hunger that makes a female eat a male.