The Wasp With a Metal-Reinforced Needle on Its Behind

A wasp lays her eggs in a fig—and uncomfortable images in your subconscious.

Few trees in recorded history have been as useful as the fig. Its leaves covered Adam and Eve’s naughty bits, for example, and the Buddha supposedly found enlightenment under one. But in India, the cluster fig tree is responsible for something far more fascinating than spiritual journeys and what must be wildly uncomfortable undies.

This tree’s figs play host to a battle between two remarkable insects: a harmless pollinator wasp and its enemy, a parasitic wasp with a metal-reinforced, serrated drill for a bum. The ultra-strong drill is thinner than a human hair, yet its owner can somehow pierce through the tough hide of an unripe fig to deposit its eggs inside—seriously ruining the day of the pollinator wasp’s own kids that are also (surprise!) hiding within. It’s like a shaolin monk throwing a needle through glass and then babies come out of the needle and OK maybe it’s not entirely like that.

A fig tree’s flowers are actually encased in the figs, as opposed to something like a highfalutin orchid’s hey-look-what-I-can-do blooms. This presents the tree with a reproductive problem: It can’t rely on the wind or a variety of insects to spread its pollen around, so instead the cluster fig enlists its own species of pollinator wasp hyper-specialized for the job.

Here’s how it goes. When a female pollinator wasp manages to sniff out a receptive tree, she lands on an unripe fig and makes her way into a tiny passageway that leads to a hollow core. The entrance is so tight, in fact, that as she crawls through her antennae and wings snap off. But that’s no bother, really. She won’t be needing those things anymore.

In the inner chamber the wasp roams about laying her eggs, spreading around pollen she picked up from the tree she was born in, and dies. (If you’re a vegan and you’ve been eating figs, that could be … bad news. But it’s not like you’re consuming whole wasps. As the fig ripens it digests the dead pollinators, so really you’re eating wasp jelly, if that helps any.) Her eggs hatch into larvae, which feed on the fig before turning into adults and mating with each other. The ever-chivalrous males chew a hole through the fig and die, allowing the females to escape and carry the pollen to new figs and start the process all over again.

Notice the ovipositor’s sheath pop off as the wasp drills deeper.

It’s an elegant illustration of coevolution between beast and plant—two species evolving side by side for millennia. “The pollinators help the fig reproduce and the fig provides the wasp with a nice nursery where her larvae can develop,” says Namrata Gundiah, a biomechanics researcher at the Indian Institute of Science.

Of course, that beautiful partnership can’t just exist in a closed symbiotic loop. That would be too easy. The parasitic wasp, Apocrypta westwoodi, would love to get inside the cluster fig as well to lay her own eggs, so her rambunctious young can devour the baby pollinators already in there.

Problem is, when the pollinator wasp climbed into the fruit, a sap-like goo sealed the entrance behind it. So the parasite has to get in the hard way—literally. She wields a super-elongated ovipositor, meaning “egg-placer.” After tapping around the fig with her antennae to confirm her victims are inside, the parasite positions the ovipositor with an impressive arch of her body and begins drilling into the fruit.

It’s no small task, considering the fig is unripe at this point. But this is no ordinary ovipositor. Incredibly, Gundiah and her colleagues found that its serrated tip is fortified with zinc, making the wicked-sharp needle strong enough to drill through the fig without shattering. Because of the toughness of her ovipositor, the parasitic wasp can drill through figs over and over, perhaps as many as 20 in her lifetime.

“The thing that caught our attention is one, [the ovipositor] has to be extremely hard to cut inside,” says Gundiah. “But also it needs to be flexible because it has to be able to maneuver within this substrate—and she doesn’t have eyes inside.”

The formidable ovipositor of the parasitic wasp. That knob at center and the little holes left of it are the sensors that let the wasp guide the needle.

Gundiah found that the tip of the ovipositor is loaded with different kinds of sensors. “Some of them we think are chemical sensors,” she says, cup-like structures each “with a neuron that would fire if the right chemical hits it.” Theoretically, this would allow the wasp to “taste” the different layers of the fruit’s skin as she drills deeper. The ovipositor also seems to come equipped with mechanical sensors that let the wasp feel around. Think of it like a finger with tongues all over it—and now try never thinking of that again.

Even more incredibly, the parasitic wasp is able to feel and smell her way specifically to the developing young of the pollinator wasp in the wall of the chamber, depositing an egg on each. All the while, the long ovipositor is bending like mad, yet does not snap. At play here, Gundiah reckons, may be tiny pits studding the ovipositor where it bends the most. These could help arrest cracks hell-bent on spreading across the structure.

It’s all the more impressive when you consider that the drill is thinner than a human hair—we’re talking some serious mechanical engineering on evolution’s part. But what’s also interesting from an evolutionary perspective is how different the parasite’s ovipositor is from the pollinator’s.

“The pollinator has a more spoon-like structure, and it’s much shorter than what you’d find with the parasitoid,” Gundiah says. Plus, “there’s a much wider repertoire of sensors on the parasitoid because she needs to sample several different aspects of her environment,” whereas the pollinator is on the inside embedding her eggs in the soft wall of the chamber, and therefore has no need for a super-sensitive ovipositor.

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