Glinting in shimmering shades of blue and green, the emerald cockroach wasp is surely a thing of beauty, but its shimmering exterior masks its cruel nature. The emerald cockroach wasp is one nature’s most impressive neurochemists. At its core, it is a parasite. The female wasp lays her eggs on a cockroach host, and when they hatch, the larvae eat the creature from the inside out. You’d think the cockroach would be opposed to this idea, but instead the insect patiently awaits its fate while the larvae mature. Cockroaches are much larger than even a full grown wasp, and certainly could put up a fight, but that is where the wasps’ ingenious manipulation of neurochemistry comes in. When she encounters a potential host, the female cockroach wasp first stings the cockroach in its abdomen, temporarily paralyzing its front legs and allowing the wasp to perch precisely on its head. She then stings the roach again, this time delivering venom directly into a part of the roach’s brain called the sub-esophageal ganglia. This doesn’t kill the roach. Instead, it puts the roach in a zombie-like trance. The roach is less fearful and loses the will to flee. It allows the wasp to lead it by its antennae, like a dog on a leash, to the wasp’s burrow where the roach will play the martyr for the wasp’s unborn children. Even though the roach is fully capable of locomotion during the week to month that passes from when the wasp stings the its brain until the hungry brood finish eating it alive, the zombified insect doesn’t move. Emerald cockroach wasps have elevated neural manipulation to an art form to create perfect living incubators.
But, though the roach has been rendered harmless, the wasp-to-be is threatened by other organisms. Humans aren’t the only species that have to worry about their food spoiling—so do emerald cockroach wasps. Cockroaches truly are dirty creatures, and their insides are home to a suite of bacteria that can harm the wasp’s vulnerable larvae. One of these potential threats is Serratia marcescens, a vile sort of Gram negative bacteria found in cockroach bodies. It’s the same bacteria responsible for a number of human urinary tract infections and the weird pink stains that form in our toilets and showers. In insects, its effects are much more deadly. The bacteria possess a suite of protein-degrading enzymes that cut apart fragile larval cells. The larvae aren’t entirely defenseless, though—as a new study published today in the Proceedings of the National Academy of Sciences reveals, larval wasps sterilize their food by secreting antimicrobial compounds.