Some Plants Attract Pollinators By Heating Themselves and It’s Probably the Oldest Pollination Strategy

Long before flowers dazzled insects with colors, ancient plants used a different signal.

We tend to think of plants as passive, vulnerable actors. But in their partnership with insects, it’s plants that often play the leading role. Sometimes, this can get pretty surprising. As evening approaches, certain tropical plants raise the temperature of their reproductive cones well above the surrounding air. The heat produces infrared radiation that nocturnal beetles can sense, even though humans cannot.

A new study published in Science shows that these plants—called cycads—use infrared radiation from heat as a signal to attract pollinating beetles. The discovery suggests that long before flowers evolved bright colors or sweet nectar, plants and insects were already communicating through temperature.

Ancient Partnership

Cycads are the dinosaurs of the plant world. Often called “living fossils,” the species growing today look strikingly similar to fossils from the Jurassic period. They don’t flower; instead, they reproduce using cone-like structures, with male and female cones growing on separate plants.

For decades, scientists have known that some cycads heat their cones, sometimes by a whopping 15 degrees Celsius (27 degrees Fahrenheit) above the surrounding air. The heat helped spread scent or provided insects with a warm place to rest.

But the timing suggested something more deliberate. Male cones heat up first, releasing pollen in the late afternoon. Female cones follow suit about three hours later. This staggered heating pattern essentially pushes and pulls insects from one plant to the next.

“This push-pull pollination guides beetles through the steps of plant reproduction,” Wendy Valencia-Montoya, an evolutionary biologist at Harvard University and lead author of the study, told The New York Times.

The targets of this campaign are beetles. Fossils show that beetles were pollinating seed plants long before bees and butterflies entered the scene. In that ancient, dim world, color wasn’t a great signal. Heat, however, stands out clearly at dusk.

Heat Signal Test

Valencia-Montoya’s curiosity began years earlier, during fieldwork in the Peruvian Amazon. While living in a tent as an undergraduate, she watched beetles find cycad cones with uncanny accuracy.

“Already I was interested in how insects, being so small, they can navigate so well,” she told National Geographic. “You see one cone, and the next day you just see all the beetles there.”

To find out how, her team designed a series of experiments that stripped away familiar cues. They built 3D-printed cycad cones and placed them near real plants. The replicas had no scent, no color, and no texture that resembled a plant.

Some of the fake cones were warmed to match real cycad cones. Others stayed at ambient temperature. Beetles overwhelmingly chose the warm replicas.

The researchers went further. They covered the heated models with a material that blocked physical contact but allowed infrared radiation to pass through. The beetles could not feel warmth by touch. They still arrived.

The conclusion was hard to escape. The insects were not following scent plumes or visual patterns. They were detecting infrared radiation emitted by heat.

“There was no real evidence that this would be a signal for pollination itself,” Nicholas Bellono, a molecular biologist at Harvard and a co-author of the study, told National Geographic.

The Antenna

Behavior is one thing; biology is another. The researchers needed to know how the beetles were seeing the heat.

At the tips of beetle antennae, they found clusters of specialized sensory cells. These cells responded strongly to small changes in temperature. When the team disabled the antenna tips, the beetles no longer reacted to infrared signals, though they still responded to scent.

At the molecular level, the key turned out to be a gene called TRPA1. Versions of this gene are already known in other animals. Snakes use it to detect the body heat of prey. Mosquitoes use it to find warm-blooded hosts.

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Finding the same gene in beetles surprised the researchers. Insects and snakes split off on the evolutionary tree more than 400 million years ago.

“Nature seems to just recycle the same old molecular players and use them again,” Valencia-Montoya told National Geographic.

Even more striking, different beetle species carried slightly different versions of the gene. Each version was tuned to the specific temperature range produced by its host cycad species. The match was precise, suggesting a long history of coevolution.

Before Flowers Turned Colorful

Early pollinators were mostly nocturnal and had limited color vision. For them, heat and scent made reliable signals. As new groups of insects evolved—active during the day and capable of seeing a wider range of colors—plants changed tactics.

Flowering plants exploded in diversity alongside bees and butterflies, evolving vivid colors and patterns. In the new study, the researchers found a trade-off across plant families: those that relied heavily on heat tended to have little color diversity, while colorful plants rarely produced heat.

“Infrared radiation is perhaps the oldest discovered pollination signal,” Bellono told NPR.

Not all experts agree that heat was the original pollination cue. “Does it mean all of them had these infrared detectors until the color evolved? I do not think so.” David Peris, a paleontologist at the Botanical Institute of Barcelona, told The New York Times.

Today, cycads are among the most threatened plant groups worldwide. Understanding how they reproduce may be critical to conserving species that rely on highly specialized pollinators.