Curtuteria Australis: The Body-Snatching Parasite

Like most worm species, Curtuteria is a hermaphrodite, with both male and female sex organs. This suits it better when there are few potential mates around (which is often when you're a highly mobile internal parasite).

In just a single lifecycle lasting a few weeks, Curtuteria australis must infiltrate and exploit the bodies of predatory birds, oysters, and whelks on the mudflats of New Zealand. It's not an easy life.

Curtuteria australis, or Curt if you will, is born as a larval worm in the belly of an oystercatcher bird. Naturally, he's soon ejected in the bird's faeces and makes a gentle landing in the coastal mudflats.

That's where the easy ride ends. Almost immediately, Curtuteria australis and his friends are eaten by whelks. If you're not down with your marine biology, whelks are a dark-shelled sea snail.

(Boiled whelk flesh is apparently delicious to humans, although somewhat less so once you know they're riddled with body-snatching parasites. Incidentally, parasitic worms can also survive in raw or undercooked cod, rockfish, whiting, mackerel, haddock, herring, salmon, squid, and eel.)

This is where Curtuteria reproduces asexually, to create a secondary larval form which is very much part of its natural lifecycle. This is what Curt wants to happen. Even if he doesn't always know it.

Now, when you find yourself in the intestinal cavity of a whelk, there's really only one exit strategy. And it ain't pretty.

For the second time in his life, Curt is expelled from his host's anus. This time, all going to plan, he ends up in the ocean.

This mass die-off is to be expected for young Curtuteria. Survival is a numbers game when organisms reproduce on mass, offering little or no parental care for their offspring. Only a lucky few make it to adulthood; a journey which requires yet another host animal.

Sweet, dear Curt. That Kraken is actually the inhalant siphon of a cockle; a type of shellfish that's related to the clam.

The cockle eats and breathes by siphoning ocean water over its gills and filtering out phytoplankton and oxygen. In the process, the cockle becomes infected with Curtuteria, unaware it has just sentenced itself to death.

It may not look like it, but a cockle can actually move. It does so by extending a muscular foot out its shell and burrowing into mud or sand.

Through countless bouts of natural selection, Curtuteria australis evolved the instinct to migrate through the cockle's body and into its foot. We'll see why in a moment.

But this is risky business for Curt. With its foot extended, the cockle is vulnerable to grazing by the foot-cropping Spotty fish. In fact, one study found that more than 80% of stranded cockles had chunks taken out of them. Curt can't survive in the Spotty fish. This new monster equates to certain death.

Now, you're burrowed deep into the muscular foot of a cockle, being jostled around at high tide, while Spotty fish take bites out of your shelter. We've all been there. To complete your lifecycle, you must reach the gut of an oystercatcher bird. How do you do it?

You make the cockle commit suicide, of course.

Curtuteria form cysts, which interfere with the cockle's muscle tissue. Eventually, the muscle atrophies and shrivels, making it useless for digging into the sand. The cockle can no longer evade predation, and lies there, hopeless and vulnerable, on the surface mud.

What's Curt thinking? He's driving his host to death! Rule number one in Parasitism for Dummies is don't kill your host—isn't it?

Actually, if you're done with your host, killing it is a very convenient way of finding your next host.

The dragon—our oystercatcher bird from the very start of this convoluted journey—finds the stranded cockle and feasts on the remains. This is how Curtuteria australis ends up back in the belly of the bird.

And this is how the intricate lifecycle of Curtuteria australis exists today. Real sneaky, evolution. Real sneaky.

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