Cockroaches hit the head to avoid becoming zombies

A wasp that attacks cockroaches turns them into mind-controlled zombies by pricking them into the brain. Cockroaches were thought to be almost defenseless against this zombie attack.

But it turns out that cockroaches have a defensive gesture that prevents them from becoming members of the undead.

Scientists have recently discovered that cockroaches were attacking their future zombie makers with karate-like kicks on the attacking insect's head. Their strategy does not kill the wasp, but that's usually enough to send them looking for an easier victim, according to a new study. [Zombie Animals: 5 Real-Life Cases of Body-Snatching]

The zombification in this wasp-cockroach scenario is a little different from that experienced by human zombies in pop culture. The human "undead condition" usually seems to spread through bites; as in some contagious diseases, an infusion of contaminated body fluid transmits the infection, turning the victim into a lively corpse endowed with a taste for the brain

However, roaches zombified by emerald wasps are not dead (at least not at first). According to the study, a first sting paralyzes their legs and a second sting to their brain provides a neurotoxin that diverts their nervous system, allowing the wasp to control its body and behavior.

After becoming a zombie, the fate of the roach takes an even more horrible turn. The wasp cuts off the end of the cockroach antenna and drinks his blood. Very refreshed, he takes the remaining stumps from the antenna and directs the roach to his nest. Then he lays an egg on the body of the cockroach and buries it inside the underground lair. Once the egg has hatched, the newborn wasp gets back into the roach's abdomen – while its zombie host is still alive.

Opposed to these pests, the only hope of a cockroach escapes the first sting – once the paralyzing pinch was delivered, a cockroach had little hope of preventing the second stabbing stroke to the brain zombie, have discovered scientists. For the new study, Ken Catania, professor of biological sciences at Vanderbilt University in Tennessee, organized 55 fights between wasps and roaches, to see if roaches had defensive movements that would work.

A video shot at 1,000 fps revealed that about half of the roaches were ambushed by the wasps without any defense. But cockroaches who defended themselves did so by standing up on their legs – "on stilts" – and kicking with one of their thorny hind legs. The kick was often tied squarely at the head of the wasp and sent the smallest insect "get lost in the walls of the room", wrote Catania.

Roach's striking power came from an uprising accumulating energy prior to the liberation of the leg, similar to the swinging of a baseball bat, according to the study. Although cockroach kicks have not always discouraged wasps, about 63% of adult cockroaches who have hit for their lives have managed to avoid being zombie. The younger roaches have not been so lucky – whether they hit or not, they almost always end up becoming wasp zombie slaves, Catania reported.

The behavior of cockroaches – who adopt a position "on guard" in the face of an attack – is not so different from the defensive strategy adopted by human victims of the zombie in horror films, Catania said in a statement. The unusual position "allows the cockroach to move its antenna to the wasp so that it can track an imminent attack and kick the wasp's head and body", as if a human could follow the movements of the wasp. a zombie with his eyes before taking off on his rotting corpse, Catania said.

"It reminds what a movie character would do when a zombie will follow him," he added.

The results were published online today (October 31) in the journal Brain, Behavior and Evolution.

Originally publishedon live science.