Our Honeybee Swarm Collection Coordinator provides this update to his advice first published last year about dealing with the newly arrived Tree Bumblebee that has a particular preference for nesting in bird boxes and can be very aggressive if disturbed or provoked ….

Bird boxes and the tree bumblebee (bombus hypnorum)

Both the above are now widespread in the UK. The problem is that the latter regards the former as its favourite nest site, and will aggressively defend its nest. Bird boxes are now very popular, and frequently given as Christmas presents. They are often fixed to houses, fences, or garden sheds, in order to attract garden birds.

For many years we have received calls about bumblebees nesting in bird boxes. However, we now have a dramatic increase of this new – to the UK – form of bumblebee, the tree bumblebee (bombus hypnorum), which particularly loves to nest in bird boxes.

For recognition purposes this bee can be distinguished from other bumblebees by its tricolour banding, with: (1) tawny red or ginger head and thorax; (2) charcoal grey or black abdomen; and (3) white tail. Photo (left) by Jeremy Early is of a male feeding on cotoneaster in his Reigate garden, from his book “My Side of the Fence”.

The spread of this species has been staggering, and with a huge human impact, since these bees favour domestic buildings and structures, requiring only a small cavity as nest space – with bird boxes as their preferred choice. The trouble arises because unlike other forms of bumblebee (which are generally docile), the tree bumblebee is easily provoked, and can often be aggressive, buzzing and even stinging people who stray close to any nest near a pathway, e.g., by a door, porch, fence, or garden shed. The risk of conflict with humans in this situation is greater if the box is fixed below head height, and, worse still, liable to vibration, which the bees hate (e.g., on a wooden garden shed, which rattles whenever the door is opened or closed).

The result often is a distress call to a beekeeper about a “swarm” of bees. But, unlike the honey bee, the tree bumblebee, as all other non-honeybee forms of bee, does not swarm, cannot be hived and in any case has only short-lived, annual nests; typically from April to June when their nests are most active.

The speed of the spread of this species across England and Wales – probably soon to reach Scotland – is remarkable. Yet this bee was only first recorded in the UK in Wiltshire as recently as 2001, having arrived probably from the continent. In Surrey it was first photographed at Egham in 2004, and later in Reigate by Jeremy Early as illustrated in David Baldock’s “Bees of Surrey”, published in 2008, when it was still described as a “rarity” in the County. However, by 2011, as Clive Hill noted in an article in the British Beekeepers Association (BBKA) newsletter – BBKA News (No. 189); the species had already become familiar to many beekeepers in England and Wales, as the cause of phone calls about “bee swarms” in bird boxes.

This is borne out by Reigate Beekeeper’s swarm statistics for our own catchment area (most of South-East Surrey) fom 2007, with no recorded cases in my swarm records from then until 2011, when I first recorded three cases. In 2012 this total shot up dramatically to 22. The next year, 2013, the total grew to 25, with four bird box removals, including two from school premises. Last year, 2014, the total exploded to a record 95 calls, with a huge surge in May – when some of our swarm collectors received 10 or more calls a day about this species, and local pest controllers even more.

Moving a Bird Box full of Bees

Investigating  incidents of bees in bird boxes takes time – and diverts us from our intended task of dealing with honey bee swarms. Moreover, moving these boxes when full of bees, as I can confirm, is not straightforward. The move has to be done at night, after the bees have stopped flying and are back in the nest. This means working in the dark, because this species will fly until then, later than honeybees. Then you have to wear protective bee gear in order to avoid being stung, working with a red light from a cycle rear lamp, because otherwise the bees will come out immediately if you shine a normal torch on the box. Before detaching the box from its fixing, you must first stop up the entrance, and then tape up all gaps and cracks – all of which may not be easy if the box is rotten or in poor condition. And then you will have to detach the box, which again may not be easy if it is nailed or screwed in. Finally, you will have to relocate the box to a chosen site, fixing it to a firm surface which is not liable to vibrate. If you are moving the box nearby (i.e., less than a mile away), you should delay removing the entrance bung for a few hours the next day to help the bees realise that they have been moved and need to re-orientate. All very laborious….

However, as already noted, time taken in dealing with these bees only diverts us from our main aim of catching honey bee swarms. Moreover, as volunteers and hobby honey beekeepers, we cannot be held responsible for this or other (i.e., non honey) forms of bee. Above all, we are not insured under our BBKA insurance scheme to deal with tree bumblebees, since this cover only extends to acts undertaken by us as part of our normal (honey) beekeeping activities.

For all these reasons, while trying our best in answering phone calls to help identify this species, and advise about their habits and lifestyle, we cannot become involved in their collection or removal. This accords with BBKA advice on its website, which states:

“Please do not call our beekeepers about bumblebees. They are unable to help you with these and will not collect/remove them. For advice on moving bumblebee nests please go to the Bumblebee Conservation Trust  website where you will find a great deal of information.”

Meanwhile, some  hopefully timely advice to follow.

As a rule tree bumblebee nests become active in April, and can remain so for about two or three months, or even through to autumn, if the Queen rears a second colony. So now – winter or early spring – while the boxes are empty is a good time to take precautions, to reduce the risk of these bees setting up home there later in the year and creating  a nuisance – and trouble for the swarm team!

What practical steps can be taken to achieve this?

• First, ensure the box is clean inside. In the case of an existing box, first take it down and open it up, to clear it of any debris from previous nesting material, and then thoroughly clean it. This will help attract birds to nest.
• Secondly, before (re)siting it, ensure that the box is well positioned for birds – see www.rspb.org.uk/advice/helpingbirds/nestboxes/smallbirds/siting.aspx.
• Thirdly (most important) avoid placing the box either (1) near a footpath or passage way; or (2) at or below head height; or (3) on a surface or structure liable to vibrate.

By following this advice now, you should reduce the risk of a tree bumblebee invasion of your bird box later in the year. Moreover, even if they do nest there then, you will have reduced the risk of their becoming a nuisance to yourself or your family, visitors, or neighbours.

In this way you can have the benefit of their pollination, and the pleasure of watching them, without the risk of you or others then being molested or stung by them – or having to call out a swarm collector!

Richard Woodhouse 9th February 2015