Read: Body-snatching wasps dominate the animal kingdom
The wasp’s strategy makes sense, because she’s not strong enough to carry a fully grown cockroach to her lair. She needs it mobile but pliable, so she has evolved a disturbingly precise venom that doesn’t kill or immobilize, but instead turns its victim into a mindless zombie. This ability, which was revealed through work by Frederic Libersat and others, has been written about extensively. But such writings, including this article, usually begin when the wasp has the upper hand. And as Ken Catania realized, that’s not always the case.
A neurobiologist at Vanderbilt University, Catania has a track record of investigating unusual animals, many of which he studies single-handedly. He has worked on star-nosed moles, tentacled snakes, naked mole rats, electric eels, crocodiles, and, er, humans. “I like getting firsthand experience about the animals I find are most interesting,” he says. “I teach about the emerald cockroach wasp, so I went ahead and got some. I thought I would just start filming them to show students and flesh out my lectures, especially the Halloween one.”
His videos, filmed at high speed, showed that the wasp’s attacks are all about the pronotum. If it gets its jaws on this plate, and delivers the first sting, “it’s game over,” says Catania. That happens roughly half the time without incident, usually when the wasp takes the cockroach unawares. But often, the cockroach defends itself.
First, it turns its flank to the wasp, stretches its legs as if standing on stilts, and tilts its head away. This not only keeps the vulnerable pronotum out of reach, but also turns the roach’s sharp leg spines toward the wasp. Those spines can inflict heavy damage, and they’re also riddled with sensitive nerves. These, combined with the cockroach’s sweeping antennae, track the wasp’s movements and warn of potential lunges. In effect, the roach becomes a living barbed-wire fence, complete with roving searchlights.
This posture has another benefit: It allows the cockroach to kick. “Crickets and grasshoppers kick defensively, but they are pre-built for it; the cockroach is not,” Catania says. “And it has a strikingly different form.” A cricket kicks outward by rapidly extending its bent legs, but a cockroach will fully extend a leg, wind it back, and then swing the whole outstretched limb like a baseball bat. “The kicks almost always landed squarely on the wasp’s head,” says Catania. “After it gets about five of these blows, it just gives up.”
Even if all of that fails, and the wasp grabs the pronotum, the cockroach still has a chance. It can now use the spines on its legs to rake the parasite off, parry its stinger, or even stab it. If it’s successful, the results can be fatal for the wasp. When Catania first acquired his wasps, he made the mistake of leaving one alone with a big cockroach. A few hours later, he returned and the wasp was dead, most likely from stab wounds.