Naked mole rats are weird. They live underground, are largely insensitive to some kinds of pain, can survive without oxygen for a long time, rarely get cancer, and can live past 30 years - decades longer than similarly sized rodents. They are also eusocial, like ants or bees: in a colony of over a hundred animals, only one female, the queen, breeds.
For a long time, scientists assumed the queen kept other females in line through bullying and violence. But that seems impractical when your kingdom is a network of tunnels stretching up to three kilometers. Now, a team from the Lewin Lab at the Max Delbrück Center for Molecular Medicine in Berlin has discovered it's actually a sophisticated olfactory signaling program.
“It’s very clear that mole rats actually have quite big noses and smell a lot,” says Gary Lewin, senior author of the study. Naked mole rats have around 1,200 olfactory receptor genes - more than mice (roughly 1,000) and way more than humans' paltry few hundred. They're also blind. “They have to be able to navigate and move around without vision, so smell is one of those things that’s enhanced,” Lewin said.
To find out how heavily they rely on smell, the team collected odor bouquets from individual animals by holding an absorbent plastic tube near a mole rat for about half an hour. Then they analyzed these scents in a mass spectrometer, separating them into around 100 distinct chemical compounds.
Based on samples from hundreds of mole rats, the team learned that each colony carries a distinguishable chemical signature. When mole rats from different colonies were placed together, they sniffed each other for about 40 seconds to decide friend or foe. If foe, they attacked, often lethally. “Naked mole rats are like humans in the sense that they’re very xenophobic,” Lewin said.
Temporarily disabling the animals' olfactory sensory neurons with chemicals made the xenophobia disappear. “They basically were cool with each other, and there was no fighting,” Lewin said.
Besides friend-or-foe signals, researchers found a specific ester called isopropyl myristate in the odor bouquets of queens - and nowhere else. “Breeding females had this particular molecule that non-breeding animals did not have,” Lewin said.
Queens secrete isopropyl myristate from their genitals and smear it through the tunnels as they roam. Tracking the compound over the queen's reproductive cycle showed it rises and falls with her fertility, peaking when she's in heat or pregnant. “It’s actually a very good marker of whether the queen is capable of breeding,” Lewin said. Plus, it's stable: researchers could still detect it in cages about 24 hours after application. Since a colony's burrow system can run up to three kilometers, “It sticks around for a while, so she has less work to spread the odor around,” Lewin added.
Pinpointing the molecule was one thing; showing what it does was another. Naked mole-rat colonies are organized in a hierarchy loosely correlated with body size. Scientists sort ranks using a dominance test: when two animals meet in a tunnel, whichever yields is lower-ranked. When Lewin's team tested how mole rats react to isopropyl myristate, the response depended on rank.
In a T-maze with the queen's molecule on one side, higher-ranked females - those with a realistic shot at becoming queen - avoided it. “We’ve got an idea, although we didn’t prove it, that in a normal environment, higher-ranked animals try to avoid the queen, because the queen might be aggressive towards them,” Lewin said.
Functional ultrasound imaging showed that puffing isopropyl myristate on the nose lights up a large part of the olfactory cortex. The team interpreted this as proof the compound registers as a distinct signal. What's more, exposure to the queen's scent triggered hormonal shifts.
Non-breeding females run high on prolactin, a hormone that suppresses fertility during lactation. Lewin's team found that prolactin levels drop when a queen is removed and climb back up once isopropyl myristate is reintroduced. Progesterone, associated with active breeding, moved in the opposite direction: low in non-breeders, rising once the queen was gone.
To be sure they had the right molecule, researchers tested what happens when the queen herself is gone but her royal molecule stays. It turned out the scent alone kept subjects in check just as well as the real queen. When mating pairs were taken away from any queen, they usually start breeding within four or five weeks. But daily sprinkling of isopropyl myristate prevented pregnancy. At the colony scale, removing a queen normally triggers the mole-rat version of Game of Thrones, with strongest females fighting to the death until a new queen emerges. But when researchers removed the queen and dosed the colony with isopropyl myristate daily for three months, there were no coup attempts. “Everything was peaceful,” Lewin says. “We had no fights. We had no females emerging as reproductive queens. The molecule was acting as a super contraceptive keeping them all sexually repressed.”
To Lewin, these results show that naked mole-rat biology is more closely tied to insect eusociality than expected. Queens in honeybee colonies and other eusocial insects use pheromones to keep workers from developing ovaries. “It’s a relatively simple mechanism that explains a relatively complex behavioral trait,” Lewin says.
What we still don't know is whether this mechanism appears elsewhere in the mammalian evolutionary tree. Because secreting isopropyl myristate is not exclusive to naked mole rats. Humans do it too. “Isopropyl myristate has been detected in the breast secretions of lactating human mothers, though its function there is unknown,” Lewin says. “This molecule or similar molecules may have effects on reproduction in species other than naked mole rats, maybe even including humans. We just don’t know that.”
The study appears in Nature, 2026, DOI: 10.1038/s41586-026-10772-5.