New experiments published in Science suggest some of the earliest plants lured pollinators not with bright petals but by producing heat that made their reproductive structures glow in the infrared. Long before showy flowers and colorful displays evolved, ancient plants appear to have boosted metabolism when pollen was ready, creating an infrared beacon that nocturnal insects could detect from a distance.
The plants in question are cycads, a group that still grows in tropical forests worldwide but is now among the most endangered plant lineages. Often called dinosaur plants, cycads changed little in appearance over more than 200 million years according to the fossil record. Botanist Wendy Valencia-Montoya, a cycad specialist at Harvard, notes their long history and modern vulnerability.
Cycads are gymnosperms related to pines. Male and female individuals each produce fleshy, cone-like structures that hold pollen or seeds—some of the earliest known organs specialized for pollen. Botanists have long observed that cycad cones can be substantially warmer than surrounding air, sometimes 15 to 25 degrees Fahrenheit hotter. Thermogenesis is uncommon and energetically costly in plants, yet cycads clearly invest in it.
Researchers have debated why cones heat up. Heat could be an unintended byproduct of metabolic activity or could help release scents, spreading volatiles the way a warmed air freshener disperses odor. Earlier studies showed male and female cones heat at different times, potentially sequencing pollinator visits. To test whether heat itself serves as an attraction cue, Valencia-Montoya and colleagues marked beetle pollinators with fluorescent tags and documented beetles arriving when cones reached elevated temperatures.
To isolate infrared radiation from other cues such as scent, humidity, or tactile warmth, the team built hollow, 3-D printed cone replicas and filled them with heated sand. These artificial cones emitted an infrared signature similar to natural cones and were deployed at the Montgomery Botanical Center in Coral Gables, Florida, to test insect responses under field conditions.
The researchers ran experiments that separated the visual infrared signal from the physical sensation of warmth. In one setup they wrapped cones with plastic that is transparent to infrared but prevents insects from touching or feeling the surface temperature. Hundreds of pollinating beetles were attracted to cones that only emitted infrared radiation, demonstrating that the infrared glow alone guided them.
When examining the attracted beetles, the team found specialized antennae capable of detecting very slight temperature differences—sensory structures functionally analogous to the heat-sensing receptors snakes use to find prey. Different beetle species visit different cycad species, and these antennae appear tuned to the temperature range characteristic of their host plant cones.
The authors argue that infrared signaling may be among the oldest pollination cues. Early insects were often nocturnal and had poor vision, so a heat-based signal would have been an effective way to locate reproductive structures. As diurnal pollinators with sharper color vision evolved, plants began to rely more on visual cues like pigment and pattern, a shift that helped flowering plants diversify rapidly.
Peer reviewers praised the combination of field and experimental approaches. Roger Seymour of the University of Adelaide called the methodological mix powerful and convincing, and he suggested a dual role for heat: beyond signaling, warm cones could help cold-blooded beetles raise their body temperature, increasing activity and the time spent on a cone, so thermogenesis might function both as an attractant and as an energetic reward.
Irene Terry at the University of Utah, who was not part of the study but researches cycad–insect interactions, noted that it is now clear cycads depend on pollinators rather than wind. She emphasized that odors are important—cycads can emit scents likened to bubblegum or bell peppers—and that the new experiments elegantly show infrared is also a vital cue. Given that some insects such as mosquitoes already use infrared information, it is not surprising beetles do as well.
The work invites us to imagine a prehistoric beetle navigating dusk and detecting plants glowing faintly in the infrared. That invisible world existed alongside dinosaurs and continues to guide beetles today as they find thermogenic cycad cones.