Nov 19

Bizarre Animal of the Week: Strepsiptera

You know you’ve got a major problem when you have another organism living inside your body, eating your innards, controlling your growth and sticking out of your rear end. If that isn’t worthy of an emergency trip to the hospital, I don’t know what is. But wasps don’t have hospitals, so if this sort of fate befalls them – and it does – then they are pretty much stuck with it.

But let me back up slightly and introduce you to the Strepsiptera, also called the twisted-wing parasites, which are strange obscure insects that spend their lives inside the bodies of other insects such as wasps. Even when they are larvae, which have fully-functional legs and eyes (see the image below), they scurry around freely within the blood of their mother.


Photo: Taylor and Francis

When they squirm free from their mother, the jostling larvae head straight for a nearby flower in the hope of encountering an unwary wasp. If a wasp lands on the flower to take a sip of nectar, one of the Strepsiptera larvae jumps onto it. The wasp, seemingly unperturbed by the sudden acquisition of a passenger, returns to its nest to feed its grubs. But this is exactly what the Strepsiptera larva wants, for as soon as the wasp arrives back at its colony, the larva disembarks from its passenger and locates a wasp grub.

A Twisted Fate

The wasp grub can do nothing to stop what is about to happen. The tiny Strepsiptera larva secretes a corrosive enzyme from its mouth, dissolving the flesh of the young wasp so that it can wriggle inside. The Strepsiptera separates the various layers of its new host and in doing so it creates a small pocket in which the parasite can hide, safe from the host’s immune system. All of the nourishment that the parasite requires is obtained solely from the grub’s bodily fluids, and this allows the Strepsiptera larva to transform into a blind maggot-like form. The change from an active, mobile larva into a limbless, grub-like stage seems to be metamorphosis in reverse, and is rarely seen in the animal kingdom.

The larva continues to feed on the innards of its host until it has grown so large that it takes up most of its host’s abdomen. It even remains with its host as it pupates into an adult wasp. The effects of the parasitism at this stage can certainly be felt. The sexual organs of the host cannot mature due to the space being taken up by the young parasite and the now-adult wasp is sterile and sexless.

By now, the Strepsiptera is getting a bit too large for the wasp. Depending on the sex of the parasite, they now take very different paths in life. If it is a male, it pupates and in the process starts to stick out from between the plates of the wasp’s abdomen, which you can see in the picture above (the Strepsiptera are the black bits poking out). When the male emerges, he fights his way out of the back end of his host and flies away, leaving the poor wasp to die. It is from the male that we get the common name of twisted-wing parasite, for his wings are fan-like and twisted over his back when at rest. The aerodynamic capabilities of these wings seem questionable at best, but it hardly matters for the male will probably only live for five hours or so. His mouthparts are too small and useless to feed him so he must find a female and mate with her before the fat reserves left over from his larval stage are used up.

And just what is the female up to while all of this is going on? Well, not much as it turns out. Strepsiptera lead such sexually-segregated lives that the females never truly pupate or even leave their hosts. All she does is poke her grub-like head from the wasp’s rear end in a scene reminiscent of a gory science-fiction film and waits for a male to come to her. Some species may force their host to climb high and stay put so that the winged male can easily locate them.

The female Strepsiptera doesn’t have a conventional genital opening – and in any case she is facing the wrong direction – so any male that happens upon her must penetrate her skin with his long, sharp penis (don’t be too disgusted by this; quite a few insects practice this) and introduce sperm to her brood canal. The young Strepsiptera hatch inside the female and travel along the same channel to reach the outside world and find hosts of their own. Their mother and her unfortunate wasp host now perish.

The Strepsiptera is a monster in miniature. It has a life cycle unlike no other animal on the planet. I don’t know why there hasn’t been a really bad monster B-movie about this parasite yet, but there should definitely be one!

And until that gaping hole has been filled, we’ll just have to make do with watching this simple video of a Strepsiptera poking out from a wasp’s abdomen.


    • Gillian Moore on November 25, 2013 at 2:40 pm
    • Reply

    Well that was a vile creature. Enlightening, sure, but utterly disgusting.

    1. The more disgusting the better in my opinion 🙂

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