Botanists may be forgetting they’re looking at flowers with the wrong kind of eyes according to a new paper by van der Kooi & Spaethe. They say that biologists need to rethink how they measure flower visibility to pollinators. While researchers have long used complex calculations based on human colour perception, these may be obscuring rather than illuminating how bees and other insects actually see their floral targets.
They argue that insects use a staged approach to flower detection with different senses coming into play at different distances. When far from a bloom, they rely primarily on scent. It’s only when they’re closer that they begin processing visual signals. Most surprisingly, colour vision only activates at very close range. van der Kooi & Spaethe give a distance of roughly 19 cm from a flower, for a flower 5 cm across for colour to make a difference. This challenges the common assumption that insects see flower colours the same way at all distances.
This staged perception of flowers is dramatically different to the human experience. For us colour is about hue, saturation and brightness. However, van der Kooi and Spaethe argue that there’s no evidence insects actually process colour the way humans do. Instead, they recommend focusing on simpler, more behaviourally validated measures like colour contrast to the background and the actual distances at which different visual processes occur for pollinators.
The difference in how insects and humans see the same flower means that our ideas of colour don’t neatly map on to the insect experience of a flower. A bland yellow petal could be alive with ultraviolet markings that we miss. Likewise, what we see as bright colours might be lost in poor colour contrast for an insect and so not register as important. As we are not the target, the genetic and structural factors that lead to flower colour aren’t necessarily going to be neatly accessible to scientists.Instead, this paper suggests we need to return to careful observation of how insects actually behave when encountering flowers in nature and follow their cues as to what matters.
van der Kooi, C. J., & Spaethe, J. 2025. Flower colour contrast, ‘spectral purity’ and a red herring. Plant Biology. https://doi.org/10.1111/plb.13767
Cross-posted to Bluesky & Mastodon.
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