Parasitic Junk in Your Trunk
There is no quicker way to clear a room at a party than to start talking about parasites that live in your skin.
The standard sci-fi trope of alien species under our flesh works because that concept freaks people the heck out. Chest-bursters, head-crabs, burrowing flesh beetles — those imaginary sci-fi creations aren’t that far from real parasites here on Earth. Behold: Strepsiptera.
This entire order of insects has a life history that will curl your toes. Adults are most commonly found in the butt-ends of wasps. Their wasp hosts serve as a full-service dining and public transportation system, as well as a hookup spot. That is generally not the sort of thing you actually want happening in your body unless you are personally involved.
In the photos above, you can see the hind end of adult strepsipterans poking out of wasp abdomens. A female strepsipteran never leaves the body of her host; she only sticks her genital region out to mate. Adult females don’t have functional wings, legs, or even a mouth. One author describes them as a “bag” of eggs and fat cells. Sex? It’s usually politely called “extragenital mating.” Which basically means the male has a stabby cock-dagger that he pokes in any likely-looking spot he can reach on the female.
Once the female is fertilized, she becomes food for her offspring. Her eggs hatch inside her body cavity and circulate around in her blood as they grow, eating her from the inside out. Creepy; but even more creepy when you know that each female produces between 2500 and 7000 eggs.
When the larvae finally emerge, they look like something from War of The Worlds. (The scale on the image below is 50 µm; that converts to 0.05 mm. So at least they are tiny alien invaders.)
The little monsters jump off the adult wasp host, and scamper over to a wasp nest’s nursery. There they use enzymes to dissolve their way into the larval wasps, drop off their legs, and get busy eating. They wrap themselves in an envelope of their own skin, and also make a blanket from their host’s skin tissue. And here is where things get really weird.
As the strepsipteran larvae develop, they also parasitically castrate their wasp host. Amazingly, wasp larvae survive having a largish parasite (or multiple parasites) inside, and are able to complete their metamorphosis to a winged adult wasp. Male wasp larvae that are infected don’t develop testes as adults. Female wasp larvae develop abnormal ovaries as adults, rather than become workers. About 4 to 10 days after a wasp larva turns into an adult wasp and begins to fly, the strepsipteran parasites wriggle out where we can see them between plates on the wasp’s abdomen.
Now the mind control begins, producing “crazy wasps.” Infected female wasps don’t help out at their nests like proper workers, but fly off and gather together at flowers in groups. They are forced by their backseat drivers to chauffeur their parasites to the scene of a floral orgy.
In a new paper out this week, researchers captured the (very short) sex life of a strepsipteran on film. Males are the only strepsipteran adults to have wings and fly. Their odd wing-shape gives strepsipterans the closest thing they have to a common name, “twisted-wing parasites.” This is what it looks like when it’s time for one of the male parasites to emerge:
Males fly around infected wasps at the flower singles-bar and impregnate as many females as possible. The video below shows a strepsipteran hook-up. The typical mating time is 3-5 seconds. Hey, don’t judge. There is no time to be wasted if you only live for 5 hours after you emerge from a wasp derrière.
The new research suggests that females aren’t passive lumps on a wasp. They participate actively in mating by “calling” to males with a chemical pheromone. Once the female is fertilized, the whole (horrifying) story begins again.
Strepsipterans are extremely difficult to study, which makes any new information about this group pretty exciting. Their taxonomy is so unclear strepsipterans are just lumped off in their own evolutionary grab bag. How exactly the larvae get from wasp to wasp, or from wasp to wasp larvae, is not fully understood. How infected wasps “know” where to go to gather together on flowers for the parasitic orgy isn’t established either.
If you’d like to pick a thesis organism, there are 600 species of known Strepsipterans, and lots of work still to be done! You can read more from the authors of this new research here, and you can look at some additional amazing photos of strepsipterans in a bee, rather than a wasp host here (in Czech).
By the way, the term “stabby cock dagger” as a synonym for insect traumatic insemination was first coined by Tom Houslay. It’s such an accurate description I think it needs to be in common usage.
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