It sounds like an experiment kids might conduct: Pairs of female jumping spiders were matched off in a mini, gladiator-like arena, while researchers recorded fight tactics in an effort to find a pattern.
What did they find? The females fight dirty.
While the males "push each other back and forth like sumo wrestlers," lead author Damian Elias of the University of California at Berkeley said in a press release, the females displayed less civil tactics.
The research is published online in the journal Behavioral Ecology.
"Males have a more gentlemanly form of combat, whereas in females it's an all-out fight," said Elias. "At the drop of a hat they start bashing and biting each other."
Another difference was that the female fights were often duels to the death, whereas males tended to resolve things through elaborate dance displays rather than fighting.
The researchers were baffled about why this happened.
"Nothing we could measure predicted which one would come out on top," Elias said. "That was really unexpected."
Finally, they hit upon a hypothesis. What if the females had a reason to fight other than territory?
They found that the females who were closer to "molting," a process that happens right before eggs are laid, were more likely to win a fight.
The researchers think this may be because molting females are much more vulnerable to predation, and so much more motivated to survive.
"In female fights it's not how big or heavy they are, but how badly they want it," Elias said.
"That trumps size and weight and whether it's her territory," he said.
"They fight until they have nothing left."