Bee invaders: Tree bumblebees and a cuckoo in the nest

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Since last writing, there has been a frenzy of bumblebee activity down at the bottom of the garden; a marked difference to May, now that nests are established and workers are on the wing. The candyfloss-like froth of the deutzia has been a-buzz; the jostling bumblebees all bumping into one another like fuzzy bumper cars, whizzing from flower to flower; intent on supping nectar and loading up their pollen sacs.

The deutzia’s pretty pale pink flowers look as though they could be crafted from sugar paste.  They’re certainly sweet enough for the bees and a whole host of other nectar-loving insects.  Nettle tap moths and flower beetles, hoverflies, butterflies, and cardinal beetles all joined the feast. 

Cardinal beetle

Red Admiral butterfly

But the guest list was dominated by two kinds of bumblebee: tree bumblebees - recognisable by their distinctive gingery-brown, black and white attire - and southern cuckoo bumblebees - distinguished by their more leisurely dining habits. 

Southern Cuckoo Bumblebee

Southern cuckoo with tree bumblebee in background

While the tree bumblebees whizzed and buzzed, the cuckoos took life a little more gently, relaxed in the knowledge that others would be bringing up their brood.  Cuckoo bumblebees behave much in the same way as their feathered namesakes.  They seek out the nests of other bumblebees, lay their eggs, then let the colony’s workers do the hard work of raising their young.  Each of the six cuckoo bumblebee species in the UK targets a specific bumblebee host.  Southern Cuckoo bumblebees invade the nests of buff-tailed bumblebees, and having spotted several buff-tailed queens in the garden this Spring (see previous post, Emergence) it’s perhaps not surprising to see lots of Southern Cuckoos as well. 

The tree bumblebees meanwhile buzzed frenetically on, oblivious to the press attention they’ve attracted this year.  Tree bumblebees arrived in the UK in 2001, and their population has been increasing ever since.  Gate crashers at the party? Not necessarily.  On the continent they co-exist with the other species of bumblebee also found in the UK, although here, where the dramatic loss of wildflower-rich habitats means less food for all our bees, a new bumblebee on the patch may add to increased competition for food.

Buff-tailed Bumblebee

On the other hand, it’s also possible that they might relieve some parasite pressure.  Tree bumblebees have been found to carry high levels of a parasite that renders other bumblebees infertile; yet many of the tree bumblebee queens studied were apparently unaffected by the parasite’s presence and still able to reproduce.

Tree bumblebee

Watching the tree bumblebees busily work the deutzia flowers, it’s clear that they are effective pollinators: gardeners’ friends indeed, and certainly welcome here at The House at Nab End.  All the more reason to fill our gardens with pollinator friendly-plants so that there’s plenty of pollen and nectar to go round.

Although the deutzia was in bloom for a good four weeks or so, the party at this end of the garden has finally come to an end.  Fallen deutzia flowers carpet the grass like spent confetti at the end of a wedding celebration, and the bees and bugs have moved on to sample other delights.  So, it’s time to get out the secateurs and prune back the shrub.  Doing it now should allow enough time for the new flowering stems to form ensuring a feast for the bees again next June. 

Thanks for reading,

 Helen D writes about simple pleasures and seasonal observations at The House at Nab End. She is a volunteer BeeWalker for the Bumblebee Conservation Trust, and her gardening is inspired by her love of the natural world.