The British habit of putting up nest boxes for birds has led to a population explosion of the tree bumblebee Bombus hypnorum.
This newcomer to Britain was first identified in 2001 when a colony was discovered in the New Forest in Wiltshire. This year it has nested as far west as Truro, in Cornwall, Pembrokeshire in Wales and Lennoxtown, north of Glasgow.
The tree bumblebee, as its name suggests, normally nests in holes in trees, but finds bird boxes the perfect habitat and has taken full advantage of the thousands of nesting opportunities provided by British bird lovers.
The bee has been widely welcomed in Britain because so many native bees, including honeybees, have been in decline and there are serious concerns about lack of bees to pollinate crops. The species seems to coexist with other bees and does not seem to compete with or damage them.
On the other hand tree bumblebees have caused some alarm to people because of the proximity of bird boxes to houses, and their use of roof spaces and even the vent pipes of tumble driers as suitable places to build a nest.
This bee is distinguished from other bumblebees because it always has a white tail, which is not seen in any British species. The bees vary in size depending on whether they are queens, drones or workers and there can be as many as 500 living in a blue tit box.
They are not normally aggressive but seem particularly averse to vibration so a nest box on a shed or anywhere near machinery can cause the bees to swarm and possibly attack the person who is perceived as the aggressor.
My neighbour had to make a run for it after knocking a nail into a wooden pergola a few feet from a blue tit box containing a bees’ nest. He avoided being stung and they soon calmed down.
This time of year the large nesting colonies of workers are already dying out having reared numerous new queens. These are currently foraging around flowerbeds and fattening themselves up before looking for a suitable hibernation site to spend the winter.
Next spring they will be among the first bumblebees to emerge and will be seen checking out the nearest nesting boxes. They prefer boxes with plenty of old bird nesting material in to give them a head start in creating their own colony. These queens are quite tough and have been known to evict blue tits from their newly built nests and take the site over.
Despite this rather unpleasant behaviour the new species’ assistance as a pollinator in early spring is particularly valuable in orchards, where shortage of bees can be a major concern.
The arrival of the tree bumblebee in Britain could have been an enterprising queen flying across the Channel, or a hibernating bee being imported in a plant container. Either way the UK has proved a perfect habitat for this species.
On the continent tree bumblebees rarely come to the notice of people. That is because other countries do not normally put up bird nest boxes close to their homes and tempt the newly emerging queens with suitable homes. Tree bumblebees therefore continue to live naturally on the edge of woods, normally quite a distance from human habitation.