New experiments published in Science show that some of the earliest seed plants attracted pollinators by producing heat that made their reproductive structures glow in infrared. Long before brightly colored flowers evolved, ancient plants known as cycads appear to have warmed their pollen and seed cones at the right time to create an infrared signal that nocturnal insects could detect.
Cycads still survive in tropical forests around the world but are now among the most threatened plant groups. Often called “dinosaur plants,” they resemble fossils more than 200 million years old. Related to pines, cycads bear separate male and female cone-like structures that hold pollen or seeds — among the oldest known pollen-producing organs.
Botanists have long observed that cycad cones can run 15–25°F warmer than the surrounding air, sometimes even hotter. Because metabolic heating in plants is energetically expensive, researchers wondered whether thermogenesis was merely a byproduct of metabolism, a way to release scent compounds, or an intentional signal to pollinators. Prior work showed male and female cones heat at slightly different times, hinting that temperature cues could guide insects between cones.
To test whether insects respond to heat itself, Wendy Valencia-Montoya and colleagues tracked beetle pollinators by marking them with fluorescent dye and recording their visits in relation to cone heating. The team also built hollow 3-D-printed cone models filled with heated sand that emitted the same infrared signature as real cones. At the Montgomery Botanical Center in Florida they ran controlled trials that separated warmth from other cues. In one setup cones were wrapped in plastic that blocked physical contact while remaining transparent to infrared, so insects could perceive the glow without feeling the heat.
The experiments found that the infrared glow alone drew hundreds of pollinating beetles. Examination of the beetles revealed antennae adapted to sense tiny temperature differences, functionally similar to heat-sensing receptors found in some snakes. Different beetle species preferred different cycad species, and the insects’ antennae appear tuned to the specific temperature ranges produced by their host plants.
The study’s authors argue that infrared radiation may be one of the oldest pollination signals. Early pollinators were often nocturnal and had limited vision, so a thermal cue would have been especially useful. As daytime, visually oriented pollinators such as bees and butterflies evolved, plants added colorful visual signals, a shift that likely contributed to the explosive diversification of flowering plants.
Independent experts praised the multilayered approach. Roger Seymour of the University of Adelaide called the work an important contribution and suggested heat might also serve as a direct energetic reward by allowing beetles to warm up and linger longer in thermogenic cones. Irene Terry of the University of Utah noted that the study complements evidence for olfactory and other cues — some cycads emit scents ranging from bubblegum to bell pepper — while elegantly showing infrared’s unique role.
The findings invite a new way of imagining ancient ecosystems: dusk-time landscapes navigated not by visible color but by warm, infrared-glowing plants guiding nocturnal beetles. That thermal signal likely helped shape early plant–insect interactions and, in some places today, still does.