Bumblebee maths

At Bumblebee Conservation Trust, we regularly hear different numbers being quoted for the ‘Number of bumblebee species in the UK’. The confusion is caused by the subtractions, additions and even multiplications of species. Let’s go through the figures, showing the working like any good maths student should.

We will start in the 1900s. Back then we had 23 known (the known part is important – we’ll come to that later) species. Then, early in the 1900s, we lost one species, Cullum’s bumblebee (Bombus cullumanus). Then in 2000, the Short-haired bumblebee (Bombus subterraneus) was also declared extinct in the UK.

That leaves us with 21 known species.

But it wasn’t long before the number was back up to 23, with the revelation that what was thought be one species, the White-tailed bumblebee, was actually three different species. All of these are similar in appearance, with only subtle differences between them. Improved genetic techniques in the 1990s and 2000s finally proved that there were indeed three species hiding under the ‘White-tailed’ name, and the three are now known as: White-tailed bumblebee (Bombus lucorum), Northern white-tailed bumblebee (Bombus magnus) and Cryptic bumblebee (Bombus cryptarum). Because they all look so similar, we just call them ‘The White-tailed bumblebee’ on our publications and website. Strictly speaking though, it is the ‘White-tailed bumblebee complex’.

Then in 2001 we actually gained a genuinely new species, the Tree bumblebee (Bombus hypnorum). This species is fairly common in mainland Europe, and it’s believed it arrived from France after arriving amongst imported goods. It has since spread throughout most of England and Wales, and has now reached Scotland too. We’re at 24 now.

But should we really be a 25? The Short-haired bumblebee was reintroduced to the UK earlier this year, as part of the Short-haired bumblebee reintroduction project. Only the queens were introduced, but the project officer has since found several workers of that species – meaning that at least one of the queens has set up a nest and successfully reared some young. While we’re very excited about this, we’re holding back from saying that the Short-haired bumblebee has finally been reintroduced to the UK. The real test will be next spring, when we will look for new queens of the species. If those are found, we can say that the bees have successfully reproduced and re-established in the UK. Fingers crossed! For more information about the Short-haired bumblebee reintroduction, read our case study.

Spot the difference: queens of the 'White-tailed bumblebee' complex (left to right: B. magnus, B. lucorum and B. cryptarum). All photos taken by Steven Falk (click here to visit Steven's excellent Flickr page on bumblebees and other wildlife).


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