The Wasp Whose Spit Gets It Laid

A female Pimpla disparis wasp doing what she does best: Injecting an egg into a pupa so her young can devour it from the inside out.

I’ve never been to a club, but then again I’ve never heard great things about them. From my understanding it’s a bunch of dudes drinking vodka Red Bulls and trying to “grind” on women, or whatever it is youth are doing these days. That seems strange to me. We’re not chimps punching the crap out of each other over the ladies, or rams headbutting each other stupid. We’re civilized human beings, for Pete’s sake.

That said, we’re certainly not the brutal parasitic wasp Pimpla disparis, whose females inject their eggs into living moth pupae. After the eggs hatch, they devour their hosts from the inside out before emerging triumphantly from the cocoons. And woe to the female disparis, who will find several males waiting for her birth, all trying to muscle each other out and hump the damn cocoon before she’s even out of the thing. This is just birth, sex, have babies. And it’s all about swapping some very special spit. (Technically speaking, insects don’t have “spit” or “saliva” as much as they have “mandibular secretions.” But I’m not going to call it that for fear of sounding like a chucklehead—well, more of a chucklehead than usual.)

I appreciate people like entomologist Mike Hrabar, because people like Mike get very expensive video cameras and point them at parasitic wasps injecting other creatures with their eggs. That’s the fruits of his labor above. Well, more accurately it’s the fruits of the wasp’s labor. That needle-like structure is her ovipositor (literally “egg placer”), and she’s not just using it to inject her young into the hapless moth pupa. She’ll also swirl it around a bit to get the insect version of blood, known as hemolymph, flowing out of the pupa, which she then drinks up. Developing those eggs, after all, takes a lot of energy, and she could use the bonus protein. The pupa certainly won’t be needing it, considering what’s about to happen next.

The wasp is specifically looking to inject its young into moths in the process of pupating, or the cocoon phase. “And then the primary larvae of the disparis basically swims inside the hemolymph of the developing moth, and it just eats it, munch munch munch, until the whole moth is eaten out from the inside,” says Hrabar. To the outside observer, the cocoon looks normal throughout this process. But instead of splitting open to reveal a moth, out comes an adult wasp—not quite as normal-looking.

Two males wait for a female to emerge from a cocoon.

Waiting for her is a nice little welcoming party of extremely randy males. As you can see below, they’re all quite keen to mate with her, forming what’s beautifully known as a scramble competition. The cocoon she’s called home can be positively covered with dudes, and enterprising fellas will even jam themselves into the cocoon with the female before she even has the chance to emerge. The stakes are quite high: She’ll only choose one male to mate with, then close off her reproductive gear.

There may be plenty of other cocoons about, so how does the male know to pick the right one? Well, in addition to giving off a bit of a smell, the developing larvae seem to be quite flirty. “The parasitoid might actually be communicating with the adult males by sonic vibration,” says Hrabar. “It actually spins within the puparium periodically, and makes these little vibrating sounds.” It even seems like the female may react to males, spinning as they fly by.

“Playing hard to get” is a concept that is almost entirely lost on male disparis wasps.

Males will follow a circuit between individual cocooned females, visiting each periodically to check on their development for up to three weeks. In a way, they’re forming their own harems, which is pretty amazing behavior for an insect. “It’s planning for a future resource,” says Hrabar. “And that is a big deal because insects aren’t thought to plan. They’re thought to have very simple brainstem type functions. So it’s all stimulus response: They need sugar, so their sugar circuits go off, and they go get sugar.” But not these wasps, apparently. They’ve got a game plan.

It’s this kind of scheming that makes wasps so scary-sophisticated. The jewel wasp, for instance, stabs into a cockroach’s brain and injects chemicals that remove its free will, allowing the wasp to drag it into a burrow, lay an egg on it, and seal the tomb up. When the egg hatches, it burrows into the cockroach and eats it from the inside out. And there are all kinds of wasps out there up to similar seriously bad behavior: The parasitic ichneumonidae family, which disparis belongs to, tallies tens of thousands of species worldwide.

For all of their plotting, though, the male disparis can end up hitting on another male, because while the male can tell if there’s a developing larva in a cocoon, he has a hard time telling the gender. “So they’re scrambling around and it just turns into this big tussle of wasps,” says Hrabar. “And then they realize, Oh, no this is male here, and they all disperse. But if it is a female, then she gets mated quickly and generally never mates again.”

That oh-so-alluring spit—really mandibular secretions.

Females do try to make it easier for the males to find them—with their spit. Males are attracted to saliva, which the emerging wasp is using to chemically break down the cocoon as it chews outward. So males literally get wind of it and fly in from all around. “If you put just a dot of that salivary fluid of an emerging female on your finger, and then stick your finger into a cage full of males, they’ll start trying to mate with your finger, which is kind of cool,” says Hrabar. He gets paid for this, by the way.

Problem is, males also utilize their spit when chewing out of a cocoon, so you end up with the occasional aforementioned male-on-male sexiness. But a female’s saliva has just a little bit more of the chemicals responsible for the scent than a male’s, and indeed Hrabar finds that statistically, males are slightly more likely to home in on a female than another dude.

Read more at Wired Science