The Insect That Devours Its Mother From the Inside Out

A male strepsiptera mates with a female embedded in a wasp. He’s far more beautiful than her, for she’s a wingless, legless sack of eggs. But it’s what’s inside that counts, and what counts for this insect is…well lots of eggs I guess.

Ah, motherhood. I don’t know anything about it, but I heard there’s a lot of, like, sacrifice and stuff. Not only do you have to bring the brat into the world, but then you have to feed it for at least 18 years or you get in big trouble. That’s a lot of pressure.

But with all due respect to human mothers out there, their sacrifice is nothing compared to a momma strepsiptera. (Cue phone call from my own mother in 3…2…1…) This little parasite invades the bodies of all manner of insects, where she waits patiently as the young that fill her body consume her from the inside out. Eventually they erupt out of their sacrificial mother and emerge from the still very much alive host insect into the light of day—as many as a million of them in one particularly large species that parasitizes big grasshoppers. Yeah, you can go ahead and throw away that “Mother of the Year” mug now.

The 600 or so species of strepsiptera are some of the cleverest, most brutal parasites on Earth. Unlike a lot of parasites out there, they have no interest in keeping their host alive for very long: They use them, abuse them, and explode out of their bodies, leaving gaping wounds that haven’t the slightest chance of healing. And their life cycle must be one of the strangest and most wonderfully complex among all parasites.

Things are very different for male and female strepsiptera. Males look like you’d expect, with wings and antennae and mandibles and big, beautiful eyes. The females? Not so much. “The female is like a bag of eggs,” said entomologist Jeyaraney Kathirithamby of the University of Oxford. “Just a mere bag of eggs.” This is no exaggeration. “The female has nothing—no eyes, no antennae. It has no mouth parts. It’s nothing.” She spends almost her entire life in the host, so what good would things like limbs do? Accordingly, she’s evolved into what is essentially just an oval of flesh.

Importantly, though, the one thing she does have are naughty bits: the oviduct. This she sticks out of the hole in her host’s exoskeleton and emits a pheromone, and the males come running. They’ll inseminate her right there on the host. You may read elsewhere that like bed bugs, strepsiptera are “traumatic inseminators,” with males stabbing into females and fertilizing the eggs through her flesh. That’s wrong, Kathirithamby stresses—insemination happens right in the exposed oviduct. So…lucky for the female, I guess?

This is what it looks like to have multiple female strepsiptera poking their oviducts out of your body.

But the male doesn’t leave straight out of his mother to find a mate. Instead, he takes a roundabout way in his development. When the female’s larvae pour out of her body, you can’t tell if they’re male or female. But you will once the young reach their own hosts, for they’ll often parasitize entirely different insects. Males, for instance, may only invade ants or bees while females only invade grasshoppers. Kathirithamby never finds the wrong sex in a certain host, suggesting that it may actually be the environment that determines what sex the strepsiptera will become. This is known as environmental sex determination. Reptiles do it too, reacting to ambient temperature to become either male or female.

The larvae will emerge from their mother in batches as their poor host continues to crawl or fly around, spreading out little nightmares for any nearby ant or wasp hives. Yet getting there is no easy task for such tiny creatures. They have legs, so they’re definitely mobile, but instead of scrambling their way to a nest they’ll cling to an adult member of the colony and hitchhike. “They actually have to be carried to the nest by a foraging worker, an ant or a wasp or a bee,” said Kathirithamby. “And when they’re taken to the nest they get onto the egg or the larvae of the host.”

Weirder still, when the strepsiptera bores into the host larva, which can take two days, it never leaves a mark. It’s likely using some kind of enzyme that dissolves the host’s cuticle, but how it does so without leaving any visible signs of trauma is a mystery. Plus, once it gets in there and develops into a male, it’ll actually allow the host larva to grow into an adult, maturing along with it in a strange kind of Calvinist predestination—the host is doomed to a horrible death right from birth. That’s real goofy, because normally the insect’s immune response would form a capsule around any foreign objects in the body cavity. But Kathirithamby never sees that happening to the strepsiptera. They do seem to wrap themselves in the inner layer of the exoskeleton, called the endocuticle, which could help them remain unnoticed.

So the male strepsiptera grows big and fat in its own little vehicle. “They need that because they want the host to be alive and moving,” and therefore be better able to disperse in the ecosystem, Kathirithamby said. And “in spite of almost the whole abdominal segment being occupied by the strepsiptera, the host is still able to move around.”

Once he’s good and ready, the male erupts out of the ant or wasp or bee and takes flight in search of a female, leaving behind the sad husk of his host. He doesn’t eat, and he doesn’t sleep. In fact, he only lives for 3 to 6 hours, so he’s in a bit of a rush. Once he sniffs out a female’s pheromones with his chemoreceptors, he dives in and mates with her on her own unfortunate host, then perishes.

The females typically go about development a little bit differently. While the larvae that will eventually become males hitchhike to their hosts, the larvae that will become their sisters stick around closer to their mother. Ideally, her host—perhaps a cricket—would have recently had its own nymphs, which the strepsiptera larvae climb into, develop into females, and begin the whole horrifying process anew.

Read more at Wired Science