Bexley flight of the (Tree) Bumblebee sets Beekeepers’ phones buzzing

David Rea, Chairman, Sidcup Beekeepers.

The second half of May 2014 has seen a spectacular explosion of activity by the Tree Bumblebee (Bombus hypnorum) in southern England. This strikingly pretty bee is common in Europe but is a new arrival in the UK, having been first identified on the South Coast in 2001. It is now north of Hadrian’s Wall and into the Welsh borders, so it’s colonising Britain quicker than the Romans did.

The very mild (albeit wet) winter of 2013 / 14 followed by a fabulous spring seems to have suited many insects, but the Tree Bumble may be setting records.

Since arriving it has found the English love of bird boxes most helpful, as they provide an ideal size and location for the bee’s nest, but this year’s population explosion – at least in the South London / North Kent area – has exploited the many holes, cracks and split tiles in house roofs.

Various members of the Sidcup Beekeepers club are listed on the web and with local councils, offering voluntary help with bee related problems, particularly with Honeybee swarms, so we are well used to calls from alarmed or nervous residents, perhaps 4 or 5 a day in the ‘season’. But the torrent that started on 15 May with a dozen calls has been awesome. On Sunday 18 May I got 48 calls – all but 2 were Tree Bumbles – and my colleagues were similarly besieged; the following week was relentless, and only now at the end of the month has the flow eased back to several a day.

How do we know the Tree Bumble is the ‘culprit’ when there are 25 different bumblebees in the UK? Well, the location – relatively high up – is one pointer, because many bumbles nest underground or low down in rockery walls, under patio decking etc often using mouse tunnels. But most easily diagnostic, and the cause of so much alarm this year, is that when the nest is fully developed many local male Tree Bumbles gather outside the entrance, circling and zooming past the hole, desperate to be the first to catch the next emerging virgin queen. This mating behaviour is unique to the Tree Bumble, and whilst it helps us with identification, it is highly visible to the householder (and neighbours) below – and disconcerting when immediately outside a bedroom window or a front door porch. Quite understandably, most members of the public presume the event is a swarm, and that something dramatic is underway. The real swarm of Honeybees on the John Lewis window in London that featured on TV during our bumble crisis only added to the panic – suddenly every second caller knew for certain that was just about to happen to them.

Luckily the general plight of bees is now well known to the public, and most are keen to avoid harming them. When told that the Tree Bumble nest causes no damage to the house and leaves no messy residue when the bees depart (about 2 months from start to finish) nearly all are relaxed enough to wait for the end. The Tree Bumble is an excellent pollinator, working much longer hours and in worse weather than the Honeybee, so the benefit for suburban gardens is significant.

Whether this tolerance will hold up if the Tree Bumble population grows enough to take over a large share of garden bird boxes is another matter altogether; blue tits, robins and sparrows may be a lot nearer to English hearts than a ‘French’ bumblebee.

For identification tips and details of a Tree Bumblebee mapping project see here:

http://www.bwars.com/index.php?q=content/bombus-hypnorum-mapping-project 

A video clip of swarming Tree Bumblebees can be seen here:

www.youtube.com/watch?v=aW2XfrKuIVk

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