This flatworm stabs itself in the head to reproduce

When some flatworms can't find a mate, a new study says, they reproduce in a way that will make you thank the god of your choice you're not a flatworm.

Danny Gallagher
Danny Gallagher
CNET freelancer Danny Gallagher has contributed to Cracked.com, Mental Floss, Maxim, Break.com, Mandatory, Jackbox Games, Geeks Who Drink and many, many other publications in his never-ending quest to bring the world's productivity to a screeching halt. He lives and works in Dallas. Email Danny.
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A microscopic image shows the anatomy of the oddly reproducing flatworm: the anterior eyes (1) in the head; the paired testes (2); paired ovaries (3); developing eggs (4); female genitalia containing three mature eggs (5); and male genital region in the tail of the worm (6). Lukas Schärer

Have you ever wondered about reincarnation, the belief that people return to Earth in the form of a different creature after they've died? It could be a good way to go. Who wouldn't want to come back as a cool animal like a majestic bald eagle in their next lifetime? Then again, there's always the chance you'll be less fortunate and come back back as a flatworm, specifically the Macrostomum hystrix species.

Why would being reincarnated as this particular type of flatworm be equivalent to a living hell? A new study suggests that it can reproduce asexually by stabbing itself in the head with its genitalia if it can't find a mate.

Researchers from the University of Basel in Switzerland and the University of Bielefeld in Germany published their study on the creature's bizarre mating habits Wednesday in the academic journal Proceedings of the Royal Society B.

Flatworms of the Macrostomum hystrix variety only resort to injecting themselves as a backup plan. Some of these little flatworms have male and female sets of genitalia, and if they can't find a flatworm to mate with, they will inseminate themselves, a practice also known as "selfing."

Researchers set up a test to see how these creatures reproduce asexually by placing them in a manipulated social environment in which some of the flatworms would be forced to resort to their "selfing mechanism," according to the study's abstract.

The researchers later noticed that some of these transparent worms, the isolated ones, didn't carry sperm in the rear portion of their bodies, but instead had most of their sperm in the front part of their bodies closer to their head. The flatworms have a "needle-like copulatory organ" that they use to inject their sperm during reproduction. So the researchers concluded that the only way the sperm made it to the head is by the worms stabbing themselves in the noggin with their, um, "copulatory organ." The sperm then traveled downward through the body toward the eggs.

"As far as we know, this is the first described example of hypodermic self-injection of sperm into the head," Steven Ramm, one of the authors of the study and a professor in the department of evolutionary biology at the University of Bielefeld, said in a statement from the University of Basel. "To us this sounds traumatic, but to these flatworms it may be their best bet if they cannot find a mate but still want to reproduce."

These flatworms may also have achieved another milestone in the eyes of nature. They are the only species that can legitimately say, "Not tonight, darling. I've got a headache."

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