To attract their pollinators, plants have long produced vivid flowers—but the world wasn’t always so colorful. Long before flowers arose and the first bees and butterflies flitted about, palmlike plants called cycads offered a different kind of lure to insects: cones that heat up to act as thermal beacons to their beetle pollinators.

Now, scientists have discovered that beetles detect these beacons with tiny infrared sensors in their antennae. Robert Raguso, a chemical ecologist at Cornell University who was not involved with the research, says the findings—published today in Science—are “supercool” because they provide a new glimpse into how plants and pollinators interact. Susanne Renner, an evolutionary biologist at Washington University in St. Louis, adds that the study makes an “entirely convincing” case that infrared radiation attracts these beetle pollinators.

Plants have evolved the ability to produce heat about a dozen times, always in their reproductive structures. The heat can be considerable. To attract pollinators in late winter, the eastern skunk cabbage raises its temperature by more than 30°C. Naomi Pierce, an evolutionary biologist at Harvard University, recalls seeing cycads at night for the first time with an infrared camera. “The cones are like beacons,” she says. “To me, that was a total eye opener.”

Pierce later found a kindred spirit in her Ph.D. student Wendy Valencia-Montoya, who became fascinated by cycads when she witnessed beetles attracted to the plants’ cones during a field trip in Colombia. It was the first time she’d ever seen beetles act as pollinators. “I just thought it was extremely cool—a reminder that pollination is not only about bees and flowers,” Valencia-Montoya says.

For her Ph.D. research, Valencia-Montoya initially sought to learn how many cycad species heat up their cones. She recorded temperatures in 18 cycad species, some in the wild and some in botanical gardens, showing the cones reached as much as 8°C above their surroundings.

Next, Valencia-Montoya conducted an experiment at a botanic garden in Florida. She placed pots with male or female cycads (Zamia furfuracea) 50 meters from one another. After collecting beetles that pollinate that species (Rhopalotria furfuracea), she put a dye on them and confirmed they were attracted by the cones—so much so that they sought out the cones’ warmest crevices.

It’s long been known that the beetles are attracted to strong scents released by cycads. To control for this effect, Valencia-Montoya 3D printed replica cones and heated them. Beetles were attracted to warm cones, coming and leaving depending on when the temperature rose and fell. The artificial cones also allowed Valencia-Montoya to show the beetles are attracted specifically to the radiant heat from infrared radiation, rather than only the warmed air nearby.

Using an electron microscope, she found that the tips of the beetles’ antennae have neurons. Studying antennae snipped off the millimeter-size beetles—work so precise that she had to give up drinking coffee—she learned that the neurons respond to heat. RNA within the neurons also revealed the activity of a gene called TRPA1, which is known from mosquitoes and snakes to be involved in infrared detection. When Valencia-Montoya coated the tips of the antennae with a molecule that blocks TRPA1, the beetles weren’t attracted to warmth.

The beetles can the tell the difference between cycad species based solely on the heat being given off. The antennae of Pharaxonotha floridana react more strongly to the temperature range of cones belonging to Zamia integrifolia, the species it prefers to pollinate, whereas R. furfuraceae antennae responded more to the warmer cones from its host plant (Z. furfuracea). Valencia also learned that in Zamia cycads, the male cones reached their peak temperature about 3 hours before female cones. That suggests the cycads are encouraging the beetles to move pollen from male cones to fertilize the female cones. “I don’t think I’ve ever seen such a detailed and thorough study of a pollination system,” says Irene Terry, a behavioral ecologist at the University of Utah who was not involved with the work.

Tellingly, the two heat-seeking beetles have unusually poor color vision relative to other insect pollinators, suggesting they might have less need to identify plants by sight. “It’s a great example of how these pollinators view the world very differently,” says senior author Nicholas Bellono of Harvard.

The fact that pollinators locate cycads with infrared could help explain the lower diversity of this group compared with flowering plants, plant scientists Beverley Glover and Alex Webb of the University of Cambridge speculate in a commentary published in Science. That’s because infrared radiation is a far less versatile signal than color, making it harder for a cycad to establish an exclusive relationship with a particular pollinator.

“Perhaps by evolving a signal only detectable by a single receptor carried by a nocturnal insect group, the insect-pollinated cycads limited their speciation opportunities,” Glover and Webb write. “The moon dance between cycads and beetles may have destined the cycads for limited evolutionary radiation.”