Dandelions and pollinators

I want you to imagine something for me. Imagine you are walking along a pavement and you see a line of dandelions sprouting from crevices at the bottom of the wall.

You see the distinctive raggedy leaves of the dandelion interspersed by punchy yellow flowerheads, possibly the occasional head has gone to seed. What emotions do you feel when you see these plants? In the past, when I saw dandelions in public places, I thought they were a symptom of an area not well maintained. A sign of a lack of care and of abandonment. Now however, I see these flowers, along with other traditional “weeds”, in a different light…

Figure 1. Common dandelion (Taraxacum spp.). Left: common dandelion amidst a swathe of lesser celandine (Ficaria verna). Right: a single dandelion flower head (pictures by author)

The dandelion actually attracts more pollinators than is expected according to it’s floral abundance, suggesting the flower is important to pollinators (Baldock et al., 2019). The flowers provide a source of lipid-rich nectar at the time of the year when a limited number of flowers are flowering (Roulston & Cane, 2000). Discovering this, I decided to investigate the interactions between dandelions and pollinators further.

A database was set up in 2022 by researchers from the University of Sussex with the goal of storing plant-pollinator interactions data recorded across the UK in one centrified data source. The database is known as “DoPI” ( The Database of Pollinator Interactions) ( Balfour et al., 2022). This new database stores information on pollinator-plant interactions in the United Kingdom gathered from a review of relevant literature dating back to 1802, and is the first of its kind (https://www.sussex.ac.uk/lifesci/ebe/dopi/). I decided to use the database in order to gain an understanding of dandelion-pollinator interactions.

The DoPI database is easy to use with a very straight forward graphical user interface. I searched for dandelions using the genus name Taraxacum as shown in figure 2. I used just the genus name as I believe dandelions as seen in the wild in the UK comprise of a number of species and microspecies, at least 150 microspecies in fact (Richards, 1970).

Figure 2. Shows how I queried the DOPI database in order to retrieve plant-pollinator interactions for the Dandelion.

This gave rise to 2413 interactions spread over 1908 rows of data. I used the programming language python in order to analyse the data in a jupyter-notebook (see below for code snippet). My key findings were as follows:

• The data recorded interactions between dandelion and 226 species of pollinator.
• The three species with the most recorded interactions were pollen beetle (249 interactions), common carder bee (192 interactions) and red tailed bumblebee (176 interactions).
• The 226 different species recorded spanned over 105 different genera, the genera with the most interactions being between Bombus (genus of mostly bumblebees), Meligethes (genus of pollen beetles) and Andrena (another genus of bees).

import pandas as pd
import plotly.express as px

# results from search for genus Taraxacum using DoPI (https://www.sussex.ac.uk/lifesci/ebe/dopi/search)
d = pd.read_csv("results/results.csv", encoding="iso-8859-1")

# number of interactions
print(d["Interactions"].sum())

# number of species of pollinators
print(d["Pollinator Species"].nunique())

d["genus"] = d["Pollinator Species"].apply(lambda x: x.split(" ")[0])

# number of different genera
print(d["genus"].nunique())

# pollinator species with top number of interactions
print(d.groupby("Pollinator Species").sum().sort_values(by="Interactions", ascending=False)["Interactions"].iloc[:5])

# pollinator genera with top number of interactions
print(d.groupby("genus").sum().sort_values(by="Interactions", ascending=False)["Interactions"].iloc[:5])

Some caveats with this analysis are associated with the nature of the collected data inputted into the database itself. The database comprises of data gathered from papers identified as relevant. This is completely dependent upon interest for a particular plant and/or pollinator. For example, if no one was interested in studying the yellow-striped daisy (I made this up), then there would be no plant-pollinator interactions recorded and a naive conclusion would be that the yellow-striped daisy is not important to pollinators, when in fact it just hasn’t been looked into. Having said this, one can at least say that a species is important if there are many interactions observed, but one cannot say a plant is not important because there are no interactions observed. I think this is a subtle yet important caveat to keep in my mind. Anyway, back to dandelions.

Despite the evidence that dandelions are good for pollinators and biodiversity, dandelions seem to get a hard time of it and I think there are several reasons for this.

The first is the dated idea that a neat lawn is good, and that dandelions are weeds that must be removed, this is no doubt a rhetoric that has been sadly perpetuated by weed killer companies such as Roundup as shown in figure 3.

Figure 3. Example of the use of a picture of a dandelion on the weedkiller “Roundup” in an advertising graphic, taken from https://www.lovethegarden.com/uk-en/roundup 30/03/2024 16.01 GMT

I believe another reason for dislike towards dandelions is more subtle. Dandelions grow well on disturbed land or urban environments such as the edge of pavements. Many of these places are in cities, a lot appearing in more rundown areas.

Could it be that, through time, we have begun to associate the dandelion with unclean or untidy places purely because they have evolved so well at living in places where other plants can’t. How many times have you seen beer cans, plastic bottles and chocolate wrappers amidst the foliage of dandelions and brambles. I believe if you see this enough, eventually you associate one with the other. I think we need to recognise that the litter is the problem, not the weeds, and change our perception of dandelions.

The impressive ability for dandelions to persist in awkward places such as pavement cracks is actually a testament to their evolved toughness, perhaps, in a time when some people are trying everything they can to destroy wildflowers by using weed killer or simply “weeding”, the humble dandelion is on the front line of fighting back.

So, let’s return back to our imaginary dandelion bordered pavement. I hope with all that’s been said in this post, your feelings towards this flower have changed. Or perhaps you have always liked dandelions, in which case, kudos to you!

Best,

Robbie

References

Baldock, K.C.R., Goddard, M.A., Hicks, D.M. et al. A systems approach reveals urban pollinator hotspots and conservation opportunities. Nat Ecol Evol 3, 363–373 (2019). https://doi.org/10.1038/s41559-018-0769-y

Balfour, N.J., Castellanos, M.C., Goulson, D., Philippides, A. and Johnson, C., 2022. DoPI: the database of pollinator interactions. Ecology, 103(11), p.e3801.

Richards, A.J. (1970), Hybridization in Taraxacum New Phytologist, 69: 1103–1121. https://doi.org/10.1111/j.1469-8137.1970.tb02492.x

Roulston, T. A. H., & Cane, J. H. (2000). Pollen nutritional content and digestibility for animals. Plant Systematics and Evolution, 222, 187–209.