Bold claim: ancient plants used heat to lure pollinators long before colorful flowers ever appeared. New experiments show that some cycads once woke up their metabolism to generate warmth at their reproductive organs, creating a thermal beacon that nocturnal insects could detect from afar. The study, published in Science, suggests that these heat-producing cycles drew in pollinators when pollen was ready, effectively guiding insects like beetles to the flowers through infrared signals rather than visuals alone.
Today, cycads survive in tropical forests around the world, though they are among the most endangered plant groups. Expert Wendy Valencia-Montoya of Harvard notes that these “dinosaur plants” dominated ancient ecosystems, and fossils show strikingly little change over more than 200 million years. The male and female cones of cycads resemble pine cones, but unlike many plants, they house both pollen and seeds in distinct structures, a feature unique to this lineage among ancient plants and making them some of the oldest pollen-bearing plants known.
Historical observations dating back centuries have noted that cycad reproductive as structures can overheat relative to the surrounding air by about 15–25°F, sometimes even more. While we often associate heat production with mammals or birds, plants can also generate significant warmth, although it demands a substantial energy investment. Earlier ideas posited heat as a byproduct of metabolism or as a mechanism to spread volatile scents—much like a scented device dispersing fragrance as it warms. Over the last few decades, research has shown that male and female cones heat up at slightly different times, a timing difference that could help direct pollinators from pollen release to seed formation.
To unravel this, Valencia-Montoya and colleagues tracked beetles visiting the cones using fluorescent tags, confirming that insects targeted the cones during the heated phases. They then built 3-D-printed, hollow pollen models filled with heated sand to isolate heat from other signals such as scent or humidity. In field tests at the Montgomery Botanical Center in Florida, these fake cones emitted infrared glow similar to real ones. In one setup, a transparent plastic barrier allowed insects to sense infrared light without being able to touch the heated surface, demonstrating that heat alone could attract pollinators.
The team discovered that beetles possess specialized antennae capable of detecting minute temperature differences—an adaptation reminiscent of heat-detecting receptors used by snakes. Moreover, different beetle species seem attuned to the precise temperature ranges produced by their respective cycad hosts, suggesting a finely tuned, species-specific thermal signaling system.
Harvard’s Nicholas Bellono describes infrared radiation as possibly the oldest known pollination cue. In the era when cycads first evolved pollen and nocturnal insects with limited vision dominated, heat would have been a practical beacon. As daylight pollinators with better vision—such as butterflies and bees—emerged, plants appear to have diversified their signaling to engage a wider range of pollinators, including visually oriented ones. This evolutionary dance between plant signals and pollinator senses helped flowering plants later diversify rapidly by expanding color palettes and patterns.
Experts not involved in the study, like Roger Seymour of the University of Adelaide, praise the multi-method approach that links cone temperature to pollinator attraction. He notes that heat might serve additional roles, such as giving heat-loving beetles a physiological boost that keeps them active longer in warmer floral environments.
Ecologist Irene Terry of the University of Utah, who studies cycads and their insect partners, emphasizes that scent remains a significant attractant for pollinators. Yet this study compellingly demonstrates that infrared heat is a crucial, previously underappreciated factor. Terry adds that insects can perceive environmental cues beyond human experience, such as infrared, which broadens our understanding of plant–insect interactions.
Imagine a prehistoric beetle navigating a dim, ancient world and perceiving glowing red signals from cycad cones. Bellono suggests this infrared “glow” would have been a remarkable feature long before humans existed—and it remains a usable sensory channel for beetles today, bridging millions of years of evolutionary history.
