Flatworms inject sperm into their heads to self-fertilize


When alone, a hermaphroditic flatworm is known to stab itself with its needle-tipped penis and inject sperm to self-impregnate. It's called "hypodermic insemination."

From Science News:

If raised alone in the lab, a tiny Macrostomum hystrix flatworm ends up with sperm distributed oddly around its body, researchers report July 1 in Proceedings of the Royal Society B. More sperm gets injected into the head and upper body and less into their rears than in counterparts with social opportunities, says coauthor Steven Ramm of Bielefeld University in Germany. He knew isolated flat worms self-fertilized somehow. The new work suggests they just curl their rears forward for a convenient jab.

"Hypodermic self-insemination as a reproductive assurance strategy" (Proceedings of the Royal Society B)