# A poppy is red to you. To a bee it is something else

A bee sees ultraviolet, blue and green, but no red. The meadow poppy looks ultraviolet to her, and her world is blurrier than yours. Look at the meadow through her eyes.

By Marius Comper · 22 September 2026 · measured spectra, under [sources](#surse)

## Can the bee see red?

The poppy is red, and bees visit it all summer. Pick one before you read on.

**The bee has no receptor for red, but red is not invisible to her.**

Her eye holds three receptors: ultraviolet, blue and green. Red fires none of them strongly, so a red flower without ultraviolet looks dark to her. Even so, bees find red flowers; it just takes them longer.

## Six flowers, seen by you and by the bee

Pick whose eyes look. The bee's colours are computed from the petals' measured spectra, by the false-colour photography rule: ultraviolet shown as blue, blue as green, green as red.

- **Common poppy** (Papaver rhoeas): red to you, ultraviolet to the bee. The petal reflects half the red (50%), but also ultraviolet (13%).

- **Cornflower** (Centaurea cyanus): blue to you, ultraviolet-blue to the bee. The petal's blue (31%) comes with ultraviolet (13%).

- **Red clover** (Trifolium pratense): purple to you, blue to the bee. The human purple hides a little blue (11%) and almost no ultraviolet (1%).

- **Daisy** (Bellis perennis): white to you, blue-green to the bee. The petal's white is really blue-green (44-48%), with a little ultraviolet (5%).

- **Dandelion** (Taraxacum officinale): yellow to you, ultraviolet-green to the bee. The yellow reflects green (31%) and ultraviolet (10%).

- **Yarrow** (Achillea millefolium): white to you, blue-green to the bee. The white is greenish blue-white (26-41%), with almost no ultraviolet (1%).

## Three receptors, 5,375 facets, three simple eyes

Inside each of the 5,375 facets sit nine seeing cells, and above them, on the crown, three more small eyes read the sky's light.

You share blue and green. The difference sits at the ends: you see red, the bee sees ultraviolet. Each sees a piece of the world the other never suspects.

Through a strip along its top, the eye draws compass information from the sky's polarised light. The three simple eyes on the crown see shapes poorly and sense light well.

**5,375 in the worker, 9,993 in the drone.**

Each facet is one pixel: the more of them, the clearer the image. The drone has almost twice as many facets as the worker, and his eyes meet on the crown.

### How blurred her world is

To catch a disc's colour, the bee needs it to cover 15° of her view: a 16 cm plate held at arm's length. She glimpses its shape from 5°, about a 5 cm plate.

Her clock, though, runs faster than yours: she catches 100 flickers a second, where your film looks smooth.

## The flower lights its own middle

The dandelion's tips and the green cup beneath them wear two different bee colours. Patterns like these guide the bee toward the flower's middle.

The flower's tips (yellow to you, ultraviolet-green to the bee) and the green cup beneath them (green to both of you) are two different signals. The difference points the way to the middle.

Many flowers wear such an ultraviolet eye: the middle absorbs ultraviolet while the petals reflect it. Look for flowers with a dark middle in ultraviolet photographs and you find them everywhere.

Ultraviolet is the bee's third colour, beside blue and green. Talk of an ultraviolet signal says more than the measurements show.

## True or false?

Eight statements about the bee's eyes. Some sound like stories and are true.

- **Bees see ultraviolet light, which your eye cannot see.** True. Bees see ultraviolet and humans do not. In return, humans see red better than bees. ([Lunau & Camargo 2025, Plant Biology](https://pmc.ncbi.nlm.nih.gov/articles/PMC12477309/))

- **Red is invisible to bees.** False. Red is not invisible, only hard to find: bees need more time to discover red flowers than other ones. ([Rodriguez-Girones & Santamaria 2004, PLoS Biology](https://doi.org/10.1371/journal.pbio.0020350))

- **The red poppy looks ultraviolet to bees.** True. The poppy petal reflects plenty of red, but also ultraviolet, and its bee category is ultraviolet. That is how bees find the poppy. ([the FReD database, spectrum 2184](http://reflectance.co.uk/indivresults1.php?id=2184&onMain=1))

- **Every red poppy in the world reflects ultraviolet.** False. In the eastern Mediterranean poppies absorb ultraviolet and are pollinated by beetles that see red. Only the western poppies reflect ultraviolet and go with bees. ([Lunau & Camargo 2025, Plant Biology](https://pmc.ncbi.nlm.nih.gov/articles/PMC12477309/))

- **A worker bee's eye has more than 5,000 facets.** True. The worker has 5,375 facets in each eye; the drone has almost twice as many: 9,993. ([Kelber & Somanathan 2019, Insects](https://pmc.ncbi.nlm.nih.gov/articles/PMC6956220/))

- **Bees see more sharply than you.** False. For its colour to register, a disc must cover 15° of her view: a 16 cm plate held at arm's length. ([Hempel de Ibarra, Vorobyev & Menzel 2014](https://pmc.ncbi.nlm.nih.gov/articles/PMC4035557/))

- **Red flowers made for birds look black to bees.** True. Red bird-pollinated flowers often absorb ultraviolet, so they look black to bees. Bees sometimes visit them to steal nectar, without pollinating them. ([Lunau & Camargo 2025, Plant Biology](https://pmc.ncbi.nlm.nih.gov/articles/PMC12477309/))

- **Bees learn blue-violet colours fastest.** True. After a single rewarded encounter, bees already recognise blue-violet well. Other colours take more tries. ([Hempel de Ibarra, Vorobyev & Menzel 2014](https://pmc.ncbi.nlm.nih.gov/articles/PMC4035557/))

## Where the measurements end

The sums above run on measured spectra and on papers read in full. Here is where they may go wrong:

- **Romanian poppies were never measured.** The poppy spectra come from Germany and Austria. Nobody measured Romania's, and the page says only what it knows.

- **The green peak is 544 or 556.** Studies give different values for the green receptor's peak. The page writes about 540, which covers both.

- **The bee's colours are a model.** The discs and false-colour flowers translate receptor signals into human colours. They show what the bee tells apart, not what she feels.

- **One spectrum appears twice.** Poppy records 2125 and 2184 carry nearly the same spectrum: one measurement published in two papers. The page uses it once.

- **The 100 flickers come from the lab.** The 100 Hz threshold was measured in free-flying bees, under laboratory conditions.

## How we know all this

Flower colours come from the FReD database, which publishes reflectance spectra measured between 300 and 700 nm. A program written for the page split each spectrum into four bands and translated the bee's three bands into human colours by the false-colour photography rule: ultraviolet shown as blue, blue as green, green as red.

Eyes and receptors come from four papers read in full: receptors and the 5° and 15° thresholds from the 2014 synthesis, facets from the 2019 synthesis, the three ocelli from the 2013 paper, and the poppy and the ultraviolet flowers from the 2025 synthesis. The hard-to-find red comes from the 2004 paper on bird flowers.

Two things you will not find here, for want of a good source: the spectrum of a Romanian poppy and a map of every meadow flower in bee view. The last would need spectra FReD does not hold.

- Peitsch, D., Fietz, A., Hertel, H., de Souza, J., Fix Ventura, D., Menzel, R. (1992). The spectral input systems of hymenopteran insects and their receptor-based colour vision. Journal of Comparative Physiology A 170. https://doi.org/10.1038/s41598-020-64782-y — the bee's three receptor peaks, 344, 436 and 544 nm (read through citing works)
- Hempel de Ibarra, N., Vorobyev, M., Menzel, R. (2014). Mechanisms, functions and ecology of colour vision in the honeybee. Journal of Comparative Physiology A 200. https://pmc.ncbi.nlm.nih.gov/articles/PMC4035557/ — trichromacy, the 5° and 15° thresholds, colour learning, pattern vision
- Kelber, A., Somanathan, H. (2019). Spatial Vision and Visually Guided Behavior in Apidae. Insects 10:418. https://pmc.ncbi.nlm.nih.gov/articles/PMC6956220/ — 5,375 worker facets, 9,993 in the drone, the polarised-light compass
- Streinzer, M., Brockmann, A., Nagaraja, N., Spaethe, J. (2013). Sex and Caste-Specific Variation in Compound Eye Morphology of Five Honeybee Species. PLoS ONE 8:e57702. https://doi.org/10.1371/journal.pone.0057702 — the three ocelli on the crown of the head
- Arnold, S. E. J., Faruq, S., Savolainen, V., McOwan, P. W., Chittka, L. (2010). FReD: The Floral Reflectance Database. PLoS ONE 5:e14287. https://doi.org/10.1371/journal.pone.0014287 — the spectra of the page's six flowers, measured between 300 and 700 nm
- Lunau, K., Camargo, M. G. G. (2025). Bees, flowers and UV. Plant Biology 27. https://pmc.ncbi.nlm.nih.gov/articles/PMC12477309/ — the poppy as a bee-ultraviolet flower, eastern and western poppies, ultraviolet guides
- Lunau, K., Verhoeven, C., Ren, Z.-X. (2018). False-colour photography: a novel digital approach to visualize the bee view of flowers. Journal of Pollination Ecology 23. https://pollinationecology.org/index.php/jpe/article/view/482 — the false-colour rule: ultraviolet shown as blue, blue as green, green as red
- Rodriguez-Girones, M. A., Santamaria, L. (2004). Why Are So Many Bird Flowers Red? PLoS Biology 2:e350. https://doi.org/10.1371/journal.pbio.0020350 — red is not invisible to bees, only hard to find