Crayfish bluff their way to top, research involving ISU prof shows

July 10 2007

While common among humans in settings ranging from the boardroom to the poker table, scientists have long believed bluffing to be rare or entirely absent in the animal world.

But an international team of researchers that includes an Indiana State University professor is calling nature’s bluff.

A new study to be published in The American Naturalist suggests dishonest signals of strength or fighting ability play a much greater role during disputes than previously imagined, at least among one species of crustaceans.

In nature, individuals often signal their superior strength to rivals to resolve territorial disputes without direct combat, thereby reducing the potential costs of engaging in fights. Male crayfish routinely use their large front claws for intimidation and fighting.

“The size of a crayfish’s claw had everything to do with whether a crayfish would dominate in an encounter," said Michael Angilletta, associate professor of ecology and organismal biology at Indiana State. “Oftentimes, smaller crayfish would see an individual with a larger claw and they would run away even though it may be an individual with a weaker claw.”

Angilletta helped analyze data gathered by Robbie Wilson of the University of Queensland, the study’s main author. While in Australia for unrelated research, Angilletta spent two months doing extensive experiments to confirm the validity of the initial study of 32 slender crayfish.

“The variation in strength is repeatable. You get these really big crayfish that have massive claws. When you get pinched by one, you think it’s going to hurt but it doesn’t hurt at all. Then you get little crayfish with much smaller claws and they can actually hurt quite a bit. For a given size claw, we found a tenfold variation in strength,” Angilletta said.

“Dishonesty during disputes may be far more prevalent than we previously imagined,” said Wilson.

As is often the case with such research, answering one question leads to additional questions.

“Is this kind of bluffing going on in other species and people just haven’t looked,” Angilletta asked.

“Our findings also challenge us to come up with a theory that can explain this exception. Here’s a population of animals that is bluffing a lot and it raises the question, ‘Why don’t other individuals call their bluff,'” he said.

“If you’re playing poker with a bunch of guys and one guy is bluffing constantly, people are going to figure him out. If you’re playing poker and everyone’s bluffing, then bluffing is never going to work, but crayfish don’t seem to recognize the bluffing. It’s a puzzle as to how this is maintained in the population.”

Contact: Michael Angilletta, associate professor, ecology and organismal biology, Indiana State University,

Writer: Dave Taylor, media relations director, Indiana State University, (812) 237-3743 or

Bookmark and Share

Story Highlights

An international team of researchers that includes Michael Angilletta, associate professor of ecology and organismal biology at ISU, has found that bluffing - previously thought to be rare or nonexistent in the animal world - is widespread among crayfish. The study is soon to be published in The American Naturalist.

Bookmark and Share