This parasitic marvel enslaves cockroaches by stinging their brains in ridiculously precise spots and injecting mind-controlling venom. The wasp then leads its zombified roach to a chamber, where it lays a single egg on its perfectly relaxed host and seals it inside with pebbles. Here the larva bores into the cockroach and feeds off its organs before killing it and emerging from its corpse into the light of day.
This is nature’s own Orkin Man — if the Orkin Man was psychologically imbalanced and just a little too excited about his job, and didn’t have all the wings and stuff. But just think of the evolution involved here. The jewel wasp has over millions of years not only developed a mind-control drug, but an astonishingly methodical brand of brain surgery to deliver it.
Sting Operation
Like any good tale, this one begins with sex. We’re not yet sure of their reproductive habits in the wild, but in captivity female jewel wasps mate once in a lifetime. Once she’s fertilized, though, she carries enough eggs to parasitize dozens of cockroaches — one egg per unfortunate bug.
The female jewel wasp will track down a cockroach by smell and sight, hitting it with a lightning-fast strike and biting onto its exoskeleton, then flexing her abdomen to jab at the bug’s vulnerable underbelly. The roach doesn’t take too kindly to this, struggling frantically and tucking in its chin in a desperate attempt to ward off what inevitably follows.
“Stinging a strong prey that’s often six times (or more) larger than yourself is not an easy task,” neurobiologist Ram Gal of Israel’s Ben-Gurion University said in an email interview. “Especially so when the venom must reach the brain of the prey, requiring delicate steering of the stinger inside the head of the cockroach. Hence, upon grabbing the cockroach by the pronotum [the armor], the wasp first injects venom inside the prey’s thorax, namely between the first (‘pro-thoracic’) pair of legs.”
The roach’s front legs are now paralyzed, the first stage of behavioral modification, allowing the wasp to pull its stinger out and jam it into the neck unimpeded. This sting is far more precise, lasting close to a minute compared to a few fleeting seconds of the first. “During this time,” said Gal, “the wasp can uninterruptedly steer its stinger through the different tissues within the cockroach’s head capsule until it finds — using specialized sensory organs on the tip of its stinger — the cockroach’s brain.”
That’s right. The wasp feels its way through the brain, depositing venom in two different spots, the supra-esophageal ganglion and sub-esophageal ganglion. Then she backs off, and at this point the cockroach does something rather unexpected for a bug that’s endured forcible brain surgery: It grooms itself obsessively for half an hour, stuck right at the spot of the attack, as if preparing for a date that sadly never comes. (I’m not trying to make this depressing, it’s just kinda happening.)
While the cockroach is preening, the wasp flies off in search of a burrow, returning as this venom-induced behavior is beginning to fade. And it’s at this time that the third stage of behavioral modification kicks in — full-blown zombification. “It will stay in this state for days, and will not self-initiate locomotion or try to escape,” said Gal.
Plight of the Living Dead
Now the wasp amputates the cockroach’s antennae and drinks its hemolymph, the insect version of blood that’s packed with sugars and proteins, allowing her to replenish energy she lost in the battle. And the cockroach doesn’t resist in the slightest. When she’s done drinking, the wasp then bites down on the stub of a gnawed-off antenna and begins leading the zombified cockroach like a dog on a leash.
But this is no ungainly zombie of popular culture. There’s no stumbling and such. The roach is in absolute control of its faculties, walking perfectly normally and fully cooperating with its master.
Once at the burrow, the wasp unceremoniously shoves the roach inside and lays a single egg on its leg, then begins collecting pebbles. With these she entombs her victim and her voracious offspring. Here, watch my kid for a bit, she seems to say.
“This takes about 30 minutes, during which the cockroach does not try to remove the egg from its leg or to escape its (yet wide open) tomb,” said Gal. “When the wasp finishes sealing the burrow, which is meant to protect the cockroaches (and the egg and developing larva) from potential predators more than prevent it from escaping, it flies off in search of a new prey.”
After about two days, the egg hatches and the larva chews a hole into the cockroach’s abdomen, feeding on the hemolymph that oozes out. It then climbs into the abdomen like Luke kicking it in the tauntaun, though unlike Luke the larva eats the organs, cleverly saving the nervous system for last. Once that’s gone, the cockroach finally dies, at which point the larva secretes an antimicrobial compound on the walls of the now-empty insect. It’ll pupate in this sanitized (it is a corpse, after all) home for a month, then finally break through the husk as an adult wasp.
Roach Coached
So what, then, was in that venom that could so thoroughly zombify a cockroach? Gal isn’t yet sure, other than it’s a cocktail of compounds, and that it appears that the same venom is used for the sting to the legs and to the brain. “We therefore assume that different components within this venom cocktail, and their different effects in different parts of the cockroach’s nervous system, are responsible for the different behavioral manipulations (short-term paralysis, grooming, and ‘zombification’).”
Interestingly, if Gal removes the egg from a zombified cockroach’s leg in the lab, it will revert to normal behavior after several days. For Gal, this suggests that the zombification is a more delicate manipulation than a total hijacking of the roach’s nervous system. In addition, remember that the cockroach will walk as it normally does, and will right itself as it typically would if you flip it over, demonstrating that sensory and motor functions are normal.
Yet it chooses to willingly follow the wasp to its doom, so what we have here is actually a conundrum of free will — that highly contentious topic you appropriately enough chose not to pay attention to in Philosophy 101 lectures (Rush did a pretty sicknasty CliffsNotes version, if you’re into the whole brevity thing). The cockroach is fully capable of fleeing, so why doesn’t it? “This implies that, like mammals, insects are not merely ‘automatons’ that react deterministically to external stimuli (a common misconception, among scientists and laymen alike),” said Gal, “but instead have a basic ability to choose when to take action and which action to take.”
“In other words,” Gal added, “and together with evidence from other insect neuroscience research, this may mean that insects have an internal representation of the external environment (similar to mammals’), as well as an ‘internal state’ that drives their motivation to favor specific behavioral actions over others in a given situation. This is what we humans often refer to as ‘free will.’”
So instead of explicitly instructing the cockroach with chemicals, as parasitic fungi do to ants to make their hosts die where the fungi can best grow, the jewel wasp could be using brain surgery to effectively remove the free will of its host. And keep in mind that all this amazing business is, at its core, just really good parenting — a creature going to an extreme to ensure the proliferation of its genes.
Read more at Wired Science
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