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Recognizing pollen

Yellow, orange, red, blue, grey or almost black: the pellets brought back to the hive offer a glimpse of the resources being exploited. Their colour can guide observation, but it is not sufficient either to identify a plant with certainty or to judge the nutritional quality of the pollen. The table proposed here should therefore be used as a field guide, not as an identification key.

1. Where does the colour of the pellets come from?

The colour of pollen depends first of all on its botanical origin. The walls of the grains and, in many insect-pollinated plants, the pollenkitt that coats them contain various pigments. Pollen can thus be yellow, orange, red, pink, green, blue, grey, brown or almost black.

The pellet does not, however, look exactly like the dry pollen present on the flower. The forager moistens the grains with nectar and secretions, then packs them into the corbiculae of her hind legs. Moisture, density, light and, later, drying or oxidation can make the shade darker, duller or slightly different (Reiter, 1947).

A few reference points are particularly conspicuous in our regions: pollen from oilseed rape and many willows is often lemon yellow, that of dandelion yellow-orange to orange, that of phacelia blue to dark blue, and that of the common poppy very dark grey to almost black. These examples remain indicative: the shades observed can vary (Kirk, 2018).

2. Can a plant be recognised by colour?

A forager often works mainly on a single plant species during one trip. A pellet therefore frequently corresponds to a dominant origin, without necessarily being perfectly pure. Colour sometimes makes it possible to formulate a hypothesis when the flowering periods and the plants visited around the apiary are known.

It does not, however, constitute a botanical signature. Several plants produce pellets of very similar shades. Conversely, a single origin can show a natural dispersion of colours depending on the variety, the maturity, the moisture, the harvesting conditions, the lighting or the observer. Recent measurements confirm that this variability severely limits classifications based on colour alone (Borlinghaus et al., 2024).

3. How should the pollen table be used?

  • Plant name: a click gives access to images or additional information where a link is available.
  • Colour: it represents the shade usually observed in the pellets. A gradient indicates several possible shades, particularly where the table groups together different species or varieties.
  • Flowering: the period given is approximate. It varies with altitude, exposure, region and the weather conditions of the year.
  • N value: it estimates, on a scale from 0 to 5, the potential nectar value of the plant, from an absence of nectar to a substantial contribution.
  • P value: it estimates, on a scale from 1 to 5, the potential quantity of pollen made available to the bees.

► Consult the file containing the list of pollens

4. Weather, flowering and actual harvest

Some plants offer plenty of pollen and little or no nectar, others provide both resources, and others are sought mainly for their nectar. These categories are useful, but they should not be treated as fixed and universal properties: the supply depends on the species, sometimes on the variety, and on local conditions.

There is no single temperature range — 21 to 26 °C, for example — that would guarantee an optimal harvest for all plants. Temperature, solar radiation, rain, wind and humidity influence the flight activity of bees as well as the release of pollen and the secretion of nectar, but not in the same way across plant species.

The choice observed also depends on the colony's demand, on the abundance and distance of the resources, on competition, on the time of day and on the experience of the foragers. A plant in flower is therefore not necessarily a resource that is actually being exploited.

5. What the beekeeper can genuinely deduce from it

  • New colours at the hive entrance probably indicate a change or a broadening of the resources being exploited.
  • Several colours observed simultaneously suggest several dominant origins, but prove neither a great botanical diversity nor a balanced diet.
  • A uniform colour may reflect intensive exploitation of an abundant flowering; it does not automatically mean a deficiency.
  • Colour gives no direct information on protein content, nor on the digestibility, freshness or sanitary condition of the pollen.
  • To follow the development of the apiary, photographing the pellets in comparable light and noting the date, the weather and the flowering plants observed is more instructive than a one-off identification from memory.

Colour is thus an excellent tool for phenological observation and a starting point for discovering the plants being foraged. It replaces neither the inspection of stores and brood for assessing the colony's supply, nor pollen analysis when botanical identification is required.

See also:

References

Author
Maurice Feltin & Robert Hummel
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