Flight puts the fight back into crickets

All it takes is a good stretch of the wings to make even a loser cricket feel like putting up his dukes to fight, according to a new study on insect aggression.

When male crickets meet, the encounter is usually not friendly. The insects first fence with their antennae. The fight intensifies as the competitors bare and lock their mandibles and then wrestle until one cricket knuckles under. The contest can end whenever one of the competitors gives up and runs away.

After a tussle, the winner remains in a combative mood, but the loser can’t muster the gumption to spar for at least 24 hours. For gamblers in China who stake fortunes on the outcome of cricket fights, a 1-day hiatus is unacceptable. Cricket handlers rile up their losing pugilists by apparently punishing them—shaking the insects and tossing them into the air 20 to 40 times. The insects immediately regain their fighting spirit.

Although the trick for resetting aggressive behavior in crickets is ancient knowledge, neuroscientist Hans A. Hofmann from the University of Leipzig in Germany doubted that corporal punishment could influence the crickets’ social behavior. “When I first did this catch and throw, I said, ‘This is never going to work,'” Hoffmann recalls. “But it did work,” he says. “Its just so unexpected.”

The key to getting a defeated cricket back into the ring is to make him fly, Hofmann, now of Stanford University, and his Leipzig colleague Paul A. Stevenson report in the Feb. 10 Nature. The researchers discovered the flight-fight connection by pitting pairs of crickets against each other, then handling the losers in different ways. They tumbled the crickets in a tube, put them in a wind tunnel, or tossed or chased them—forms of stress that cause the insects to release hormones that might induce aggressive behavior. However, only crickets that had flown during the procedures were ready to engage new opponents.

In crickets, separate nerve centers control flight and aggression. The brain governs fighting, while a command center in the thorax sends signals to flight muscles.

When the researchers cut the connections between the centers, losing crickets stayed deflated even after flying. The connecting neurons must transmit a signal—from muscles to the brain—that resets aggression, says Hofmann.

A new cricket on the block probably fights to win mates and territory, so linking flight to aggression would allow a migrating insect to arrive ready to rumble, he says. “We really know little about links between behaviors, and [this study’s] a very nice example of that,” says Ann V. Hedrick of the University of California, Davis. Researchers have documented links between complex behaviors—such as mating and avoiding predators—but this may be the first example of a physical activity influencing social behavior, she says.

The new study correlates well with findings by Ron Hoy of Cornell University and his colleagues. They have shown that concentrations of octopamine—insects’ flight-or-fight hormone—go up in the blood of fighting and flying crickets but hold steady in fleeing insects.   “It’s kind of hard to interpret what this all means,” Hoy says, because crickets generally don’t fly away after a fight.

Hofmann hopes his study will prompt psychologists to reexamine links between complex human behaviors. A physical-social behavior link may explain the antidepressant effect of sleep deprivation, he speculates.