Bumbler bees and foxgloves

Digitalis purpurea flower guard hairs
Digitalis purpurea flower guard hairs

Sometimes when you take a photograph you only notice something unusual about it when you come to examine the image closely on the computer. I took this image of a foxglove flower – something about the inside of the flower caught my attention – but it was only when I looked closely at the image that I noticed the hairs standing up on the inside, on the lower surface. What were these for? Most things have a purpose in nature don’t they?

I little bit of Googling later, I found out that Charles Darwin had been here long before me. In his book, The effects of cross and self fertilisation in the vegetable kingdom, Darwin writes:

Humble-bees [=bumblebees] can crawl into the dependent flowers with the greatest ease, using the “hairs as footholds while sucking the honey; but the smaller bees are impeded by them, and when, having at length struggled through them, they reach the slippery precipice above, they are completely baffled.”

Digitalis purpurea flower cluster
Digitalis purpurea flower cluster

Scrupulous as always in referring to the contributions of others, Darwin was quoting another naturalist, a certain Thomas Belt (1832 – 1878), who was clearly no slouch when it came to observing nature (2). So it was Belt, it seems who made these observations about the hairs keeping out smaller bees and other insects. He was clearly an acute observer of the natural world. Strangely, these remarks appear to have been made in a book called, The naturalist in Nicaragua, although the actual observations were made in north Wales (2). Alfred Russel Wallace reviewed Belt’s book in 1874, and described him as “a close, an accurate, and an intelligent observer. He possesses the valuable faculty of wonder at whatever is new, or strange, or beautiful in nature; and the equally valuable habit of seeking a reason for all that he sees.”(3)

So it seems that the guard hairs deter smaller bees from entering the foxglove flower. The reason being that the flower is effectively selecting large bees to pollinate it, particularly long-tongue species, such as Bombus hortorum, which can reach deep inside the flower to get the nectar (4).

Long-tongued bumblebee
Long-tongued bumblebee

However, it seems that other bumblebees, including those with short tongues are able to collect pollen from the foxglove flower (by ‘buzzing’) although it seems that they are unable to reach far enough down to the nectar source to obtaion any nectar (5).

I also discovered a lovely poem, by a poet I had not heard of until now – called Anne Stevenson – who beautifully captures the biology of the bees and the foxglove flowers in her verses. As acute a description as that of Belt in a way.

The Miracle of the Bees and the Foxgloves

Because hairs on their speckled daybeds baffle the little bees,
Foxgloves hang their shingles out for rich bumbling hummers,
Who crawl into their tunnels-of-delight with drunken ease
(See Darwin’s pages on his foxglove summers)
Plunging over heckles caked with sex-appealing stuff,
To sip from every hooker an intoxicating liquor
That stops it propagating in a corner with itself.

And this is how the foxglove keeps its sex life in order.
Two anthers – adolescent, in a hurry to dehisce –
Let fly too soon, so pollen lies in drifts about the floor.
Along swims bumbler bee and makes an undercoat of this,
Reverses, exits, lets it fall by accident next door.
So ripeness climbs the bells of Digitalis flower by flower,
Undistracted by a mind, or a design, or by desire.

  1. Darwin, C. R. 1876. The effects of cross and self fertilisation in the vegetable kingdom. London: John Murray.
  2. https://archive.org/details/naturalistinnica01belt
  3. http://people.wku.edu/charles.smith/wallace/S238.htm
  4. Broadbent, Arthur, and Andrew Bourke. “The bumblebee Bombus hortorum is the main pollinating visitor to Digitalis purpurea in a UK population.” Journal of Pollination Ecology 8 (2012): 48-51.
  5. http://abugblog.blogspot.co.uk/2013/06/watching-bees-on-foxgloves.html
  6. http://www.theguardian.com/books/booksblog/2013/oct/21/poem-of-the-week-anne-stevenson


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