- Males who shed their sperm-containing sacs are lighter and more agile.
- Scientists believe this may make males better able to fight off competition.
Male spiders castrate themselves so their manhood doesn't weigh them down when they're fighting off competitors, say researchers.
Associate Professor Daiqin Li from the National University of Singapore, and colleagues, report their findings today in Biology Letters.
"The eunuch males are better fighters because they are lighter and they have an increased endurance," says Li, an expert in animal behavior.
"They try to prevent the other males from mating with the female."
In a number of spider species, the females are much larger than the males and more aggressive.
Li and colleagues studied one tropical species called Nephilengys malabarensis in which the female cannibalizes the male during copulation.
Not only that, but what has really puzzled researchers until now is that during mating the males break off one or both of their sperm-containing palps.