Cuckoo Bumblebees

*Originally posted in May 2015 on

One flew east, one flew west, one flew over the cuckoo’s nest.


Cuckoos, by the way, don’t have one.  A nest, that is.  They lay their eggs in the nests of other birds, leaving their young to dispatch the host eggs and be reared by the unsuspecting, and remarkably doting host parents.  It is this tactic employed by a subspecies of Bumblebees called Psythrius, and the reason that we call them Cuckoo Bumblebees. Of the 24 species of UK Bumblebees, six of them are cuckoos.  They don’t have workers; just males and queens, as the queen will enter the nest of her ‘host’ (which she often looks very similar – this is an example of Wasmannian mimicry as opposed to the Batasian mimicry I’ve blogged about before).  The cuckoo queen will kill the host queen, lay her own eggs, and use the host workers to raise her brood for her!


I taught a course in the summer on ‘Bumblebee Identification for beginners’ at the new Arboretum Visitors’ Centre in Walsall.  One of the first things we look at is how to tell whether you’re looking at a ‘True’ Bumblebee or not – as this helps in identifying the species. So how do you tell the difference between Cuckoo Bumblebees and True Bumblebees? It’s all in the legs.

If you take a look at the two similar photos below, and take a close look at the hind leg of these two similar bees – you’ll notice that the top bee’s hind leg has a shiny surface, and the bottom bee’s hind leg is dull and hairy.  This is the main feature to separate cuckoo bees from true: the top bee is the Red Tailed Bumblebee (Bombus lapidarius) and the bottom is the Red Tailed Cuckoo Bee (Bombus rupestris).


Of course, you have to look pretty close (usually in a bug pot, and with a hand lens) to see this feature, so there are a couple of other features you can look out for.  The first is the wings, which on a cuckoo bee (As in Bombus campestris below) are often very dark compared to the true bumbles (look at the difference in the wings of B. rupestris and B. lapidarius above).


Another key feature to look out for is the abdomen (This is a tricky one, but useful once you get your ‘eye in’).  Cuckoo bees tend to have a slightly ‘pulled-out’ appearance to their abdomen, as if someone has tugged on the end and separated the segments slightly.  You can often see the surface of the abdomen between bands of fur, whereas in true bumblebees you can usually only see fur.  Take a look:


I hope this helps with your bee identification, so happy hunting!

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Author of, bat worker, darwinist, entomologist, knitter, gamer, SF reader & basket maker. Chair of @BrumBats

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