Octopus Sex Just Got Weirder. In Addition to Depositing Sperm, Males’ Specialized Mating Arm Can ‘Taste’ Female Hormones

The hectocotylus is both a reproductive organ and a sensory organ, a rare combination in animals, new research suggests

April 9, 2026

an octopus in front of a background of marine plants — The researchers primarily studied California two-spot octopuses. Jerry Kirkhart via Wikimedia Commons under CC BY 2.0

Octopus sex seems like a very dignified affair. A male octopus hands his sperm to a female using one of his eight arms to place a spermatophore—a seed-filled packet—into the female’s mantle cavity, which contains her ovaries. She can then store the sperm until she’s ready to fertilize her eggs.

It turns out, however, that the male’s specialized sex arm, or hectocotylus, is more than just a mating organ. In a study published April 2 in the journal Science, researchers reveal that the hectocotylus is also a sensing organ that can “taste” certain female-produced chemicals, allowing male octopuses to find mates without seeing them.

“It’s very uncommon that animals merge sensation and reproduction in a single organ,” study co-author Pablo Villar, a biologist at Harvard University, tells the Washington Post’s Fenit Nirappil.

Fun fact: A record-breaking octopus might not be an octopus after all

A study published this month suggests that the earliest known octopus—from a 300-million-year-old fossil—is actually another animal, probably a nautilus relative.

The surprising discovery began with another curious observation. Villar found sensors on the hectocotylus exactly like the sensors on the animals’ other limbs. That surprised him, given that the reproductive arm normally isn’t used for identifying food or inspecting the environment.

To investigate the matter, Villar and his colleagues put California two-spot octopuses into a saltwater tank. One male and one female went in, separated by a black barrier with openings on the sides just big enough for the cephalopods’ arms. That was meant to get the animals acquainted with one another, reports National Geographic’s Chiara Marchisio, but the male ended up reaching out to the female and putting his hectocotylus into her mantle.

“They mated through the divider,” Villar says in a statement. “For us, that was the simplest and most clear demonstration that they can recognize each other just using chemosensation”—detecting chemicals in the environment, like via taste and smell—“and mate with no full body contact.”

Comparable dynamics took place between different couples, with mating successfully occurring in the dark, too. These pieces of evidence, in addition to male octopuses never trying to mate with one another, indicated the presence of a female sex signal. During a closer examination, the team found that the ovaries were full of precursor molecules for the sex hormone progesterone.

Progesterone, which is primarily produced during female octopuses’ reproductive phase, proved to be a significant trigger. Male octopuses tried to mate with progesterone-smothered tubes on the other side of the divider, but they didn’t reach for tubes covered in other sex chemicals. What’s more, an amputated hectocotylus even moved in the presence of progesterone.

Further experiments revealed that progesterone binds to a protein called CRT1 on the hectocotylus. Researchers have already recognized CRT1 for its role in helping octopuses detect microbes on the surface of prey, so it seems to serve multiple purposes.

“It makes sense that the arm is both the sensor and the mating organ, because in these chance encounters, the arm has to be able to both localize the female, localize the [egg passageway] and very quickly initiate the mating or move on,” study co-author Nicholas Bellono, a biologist at Harvard University, tells the Guardian’s Nicola Davis.

The hectocotylus’ sensory abilities mean females probably don’t have to communicate in a “showy” way that they’re open to mating, Heather Rhodes, a biologist at Denison University who did not participate in the study, tells National Geographic. “He’s just eavesdropping on her natural hormone profile.”

Still, researchers don’t know whether all octopus species mate in this manner or what role this sensory system might have in evolution, Elena Gracheva, a neurophysiologist at Yale University who was also not involved in the study, tells Scientific American’s Cody Cottier. “I would say that this is just the beginning of the discovery.”

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