Here’s how cockroaches fight off zombie-makers
When attacked by brain-stinging wasps, kicking really helps
New video of real-life fights against zombie-makers offer plenty of tips to avoid undeath. Fortunately, the zombie-makers’ targets are not humans but cockroaches. Tiny emerald jewel wasps have stingers. It they succeed in stinging a roach’s brain, that roach becomes a zombie. It will submit total control of its walking to the will of the wasp. So the roach has a lot of incentive to not let the wasp succeed. Whether the wasp does tends to depend on how vigilant the roach is. And how much it kicks.
Female emerald jewel wasps (Ampulex compressa) seek out American cockroaches (Periplaneta americana). The wasp is a deft and focused attacker, observes Kenneth Catania. He works at Vanderbilt University in Nashville, Tenn. He has made a new and impressive collection of slo-mo attack videos. They give the first detailed look at how roaches fight back. And, he notes, what the roach has to learn is that that predator is “coming for your brain.”
If a wasp succeeds, it leads away the roach like a dog on leash. The roach puts up no protest. All the wasp has to do is tug on one of the roach’s antennae.
The wasp lays a single egg on the roach. Then she buries the egg and the undead meat that will feed her young, known as a larva. A healthy roach could dig itself out of its untimely grave. But those stung by these wasps don’t even try to get out.
It’s not mere ghoulish interest that fueled his research. These new videos of how a roach tries to defends itself open up a range of research questions. Among them: How did behaviors of the two insects — predator and prey — lead the roach to develop its defenses and the wasp to engineer its attacks.
A one-two punch — or sting — to the brain
Catania videoed the attacks as both the wasps and roaches were confined in a space at his lab. To avoid being leash-walked to the tomb, a roach needed to stay vigilant. In 28 out of 55 attacks, roaches didn’t seem to notice the threat quickly enough. An attacker needed only about 11 seconds, on average, to ease close — and conquer. The roaches who remained aware of their surroundings, however, fought back. Seventeen managed to hold off the wasp for a full three minutes.
Catania counts that as a success. In the wild, a jewel wasp would probably give up after such a feisty battle or the cockroach could escape with its life. Catania described his battle videos October 31 in the journal Brain, Behavior and Evolution.
The wasp has no interest in killing its prey. She needs her victim not only to be alive but also to be able to walk. Otherwise the tiny momma wasp would never be able get a whole roach to the chamber where she will lay her egg. Every wasp needs living roach meat to start life, Catania notes. And when she succeeds, a mother wasp can subdue a roach twice her size with just two precise stings.
She starts by jumping on the roach and grabbing the little shield over what’s basically the back of its neck. Within literally half a second, the wasp is positioned to deliver a sting that will paralyze the roach’s front legs. This leaves them useless for defense. The wasp then bends her abdomen around. She quickly feels her way to the soft tissues of the roach’s throat. Then the wasp stabs up through the throat. The stinger itself carries sensors and delivers venom to the roach’s brain.
The wasp doesn’t have to do anything else — just wait.
After this attack, a roach will typically start grooming itself. This may be a reaction to the venom. The roach “is sitting there not running away from this really terrifying creature that’s going to eventually ensure it gets eaten alive,” Catania says. It doesn’t resist. Even when the wasp bites the roach’s antenna down to a half-length stub and takes a drink of its insect version of blood.
“There’s a lot of recent interest in the jewel wasp, and for a good reason,” notes Coby Schal. He studies other roach behaviors at North Carolina State University in Raleigh. Both wasps and roaches are relatively large. And that has made it relatively easy to explore how their brains and nerves affect their behaviors.
Alert roaches may hold off becoming zombies
Some roaches notice the approaching wasp. The most effective defensive move is what Catania calls “stilt standing.” The roach rises tall on its legs. It makes a barrier “almost like a barbed wire fence,” he says. While the Halloween roaches Catania bought for his own kitchen have misleadingly smooth legs, real roach legs are not. These sensitive limbs bristle with spines that can stab a wasp.
As a fight wears on, the roach may turn and, with one of its rear legs, repeatedly kick its attacker in the head. A roach leg isn’t built for a straight kick. So to manage this maneuver, the roach instead swings its leg sideways. It moves a bit like a baseball bat.
Juvenile roaches don’t have much of a chance to fight off one of these wasps. “Zombies are hard on the kids,” Catania says. A full-grown adult roach may, however, avoid becoming a larval wasp’s breakfast, lunch and dinner.
The fights might go differently outdoors, Schal says. A roach might dart into a little crack or run down a hole. It’s a more complex fight. He has seen them in real life, in such places as his own backyard in North Carolina.
Outdoor roaches have to deal with other predators besides wasps. Schal wonders if their quirks affect how the wasp-roach fights play out. For instance, scary toads will zap out their tongues to snatch up a roach to eat. Over time, roaches have learned to notice air whooshing in their direction. That might be their last split second to dodge a toad tongue or some other attack.
Shal wonders whether the roach’s rapid response to air movements has something to do with the way the wasps approach. They can fly perfectly well. But they don’t dive into their victims. As they close in on a roach, they find a place to land. Then they creep in close. That sneak attack may be a way around a roach’s ability to dodge attacks from the air.
People don’t really have to worry about zombie-maker attacks. But Halloween is the season for imaginary scares. For practical advice, in case fictional zombie-makers jump off a movie screen, Catania advises: “Protect your throat!”
Such advice is a bit late for him, though. His Halloween costume this year? A zombie, of course.