The emerald jewel wasp (Ampulex compressa) is renowned for its ability to zombify the American cockroach (Periplaneta americana) with a sting to the brain. When the venom takes effect, the cockroach becomes passive and can be led by its antenna into a hole, where the wasp deposits an egg and then seals the exit with debris. In a new study, Vanderbilt University’s Professor Ken Catania has found that for a cockroach not to become a zombie, the best strategy is: be vigilant, protect your throat, and strike repeatedly at the head of the attacker.
“The ‘zombification’ of the American cockroach by the emerald jewel wasp stands out as one of the most remarkable and well-studied examples of host behavioral manipulation by a parasitoid,” Professor Catania said.
“In order to reproduce, the emerald jewel wasp must somehow lead its much larger victim to a chamber, glue an egg to the cockroach in just the right spot, and seal the chamber with debris.”
“The host, which could dig its way out, must instead remain passively in the chamber while it is slowly eaten alive by the developing wasp larva.”
In the study, the interactions between cockroaches and jewel wasps were investigated by high-speed video to determine the range of defensive behaviors used by cockroaches and to document the wasp’s attack strategy.
Many cockroaches detected the wasp as it approached, and they were able to mount a successful defense by stilt-standing and kicking, or by removing the wasp with an escape response combined with a raking defense with the tibial spines of the limbs.
“I saw that, before the wasp can get into position and deliver its sting, the cockroach uses a swift blow with a spiny back leg to deter its attacker,” Professor Catania said.
“The good news for the cockroach: the defense worked for 63% of adults that tried it. The bad news: juveniles almost always failed and got stung in the brain.”
“The cockroach has a suite of behaviors that it can deploy to fend off the zombie-makers, and this starts out with what I call the ‘en garde’ position, like in fencing,” he added.
“That allows the roach to move its antenna toward the wasp so it can track an approaching attack and aim kicks at the head and body of the wasp, and that’s one of the most efficient deterrents.”
“It’s reminiscent of what a movie character would do when a zombie is coming after them.”
“The wasp usually figures out there’s a smaller and less defensive cockroach out there to be had.”
The findings appear in the journal Brain, Behavior and Evolution.
K.C. Catania. How Not to Be Turned into a Zombie. Brain Behav Evol, published online Ocotiber 31. 2018; doi: 10.1159/000490341