This predatory flatworm, native to tropical and subtropical regions but now invasive worldwide, stalks and then kills the good guys – aka earthworms – with grisly aplomb.


Sensory organs on the underside of its unusual hammer-shaped head help the worm to detect its prey, which it then pins down with its head and body. The predator’s mouth, which is located halfway down its body, opens wide, and the back portion of the mouth extends forwards to form a sheet which then clamps around the earthworm.

Digestive enzymes are secreted, turning the earthworm’s body into a tasty soup, which is then sucked up by the predator. When the job is done, any undigested material exits the worm the same way that it entered. Yes, that’s right, the hammerhead worm’s mouth is also its anus.

Like all good Netflix villains, the hammerhead worm is also toxic. At least two species produce a neurotoxin called tetrodotoxin, which they use to help subdue prey up to 100 times their own mass.

They’re also relentless.

Chop them into pieces, and the feisty worms regenerate, making them seemingly immortal… unless you are familiar with the hammerhead worm’s Achilles heel, which is, in fact, just a dip in soapy water.

So maybe they’re not so scary after all!

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Helen Pilcher
Helen PilcherScience writer, presenter and performer.

Helen Pilcher is a tea-drinking, biscuit-nibbling science and comedy writer, with a PhD in cell biology.