Male Crayfish Like a Good Fight

March 5, 2008 -- Human parents may worry about the effects of TV violence on their kids, but among male crayfish, watching a fight appears to actually chill aggression.

That finding adds to the growing body of evidence that individuals, particularly males, of many species watch competitive encounters. Viewing such events either seems to stimulate further aggression, or lessen it.

"Think about the problems some countries have during soccer matches," said Paul Moore, who co-authored the crayfish study. "Observing the competition, especially if there are a lot of fouls, tends to [intensify] the aggression in the audience."

"The concept of watching fights and having this experience change the potential outcome of the next encounter is something that matches with both studies and anecdotal evidence," added Moore, who is a professor in the Department of Biological Sciences at Bowling Green State University.

Moore and colleagues Thomas Zuland and Rebecca Zuland-Schneider chose to study crayfish because the aggressive shellfish form dominance hierarchies and engage in ritualized fighting.

During a typical fight, the crayfish approach each other with their big pinchers, chelae, out as far as possible. They then go into what is known as the "boxing phase," during which the "crayfish spend considerable amounts of time pushing and not pinching with their claws," explained Moore.

If nobody backs down, the fight escalates as the crayfish use their pinchers to grab at each other. Like wrestlers, they attempt to flip over their rivals or forcibly move them around.

If both competitors are still standing at that point, the fight reaches a final, brutal stage.