The ‘Tree Bumblebee’

The ‘Tree Bumblebee’ (Bombus hypnorum) is a recent arrival in the UK, but has become a familiar guest to those with domestic and commercial premises in England and Wales, and to the nation’s beekeepers. This recent arrival is held with great affection by many in the UK and was first detected here in Wiltshire in 2001. The natural distribution of the species covers Mainland Europe through Asia and up to the Arctic Circle. The Tree Bee has spread rapidly in the UK and by 2013 it had reached southern Scotland. The rapidity of the species’ propagation and spread across the UK is explicable by its tendency to build nests in bird boxes. Bird boxes are very popular in the UK of course.

Common bumblebees in the UK are identifiable by the colour patterns on the banding of their fur. Bombus hypornum’s banding is rightly considered to be unique when we take into account the species as a whole. The thorax is tawny/ reddish brown, the abdomen is black and it has a white tail. There is little difference in the colouring between Queens, workers and male drones. Drones appear heavier, or chunkier – around double the size of a honey bee. New or fresh drones are distinguishable by a patch of facial fur, which eventually wears off. The size of Queens varies significantly with an ambit of variation similar to that of the Whitetailed bumblebee (Bombus lucorum). The workers are quite small in size. In terms of colouring the thorax is the biggest variable – dark Tree Bees are commonly identified, but they are always handsomely adorned with a white tail. Often the fur is very worn on the central part of the thorax giving an impression of a tendency towards baldness, which can amplify the effect of appearing dark in colour.

A common cause of concern for those with domestic or commercial premises relates to the fact that the Tree Bee frequently establishes nests in bird boxes or within certain parts of buildings. It often appears to be the case that the bees display a high level of nest flight activity owing the surveillance of the nest by the drones. Another cause of concern is the tendency of the Tree Bee to react rapidly with defensive behaviour when a nest experiences vibration. A further common cause of concern to people is the sound of bee activity heard through ceilings and walls. People tend to experience an amplified level of concern because the preferred nesting sites – bird boxes – tend to be near domestic premises: they become more obvious to us. HOWEVER, by the time the location of a nest has become obvious to us, because of nest surveillance by drones and general activity, it is at the point in its life when the activity is soon to decline naturally. This will be towards the end of July, that is, for Spring-formed colonies. In most cases, therefore, there really is very little cause for concern.

An area in which further study is required is the ‘chattering’ sound made by colonies, usually in loft space above upstairs rooms. This noise seems to occur during hours that are somewhat anti-social or humans. We are still learning about how to deal with this issue. An interesting observation about the species identifies a higher rate of reports relating to Tree Bee problems in the UK when compared with those on mainland Europe and Asia. It is believed that this difference results from the fact that the UK has such a large number of bird boxes when compared with Europe and Asia.

The Tree Bee is one of the first bumblebee species to be seen in the spring. Within an entirely natural context it is a woodland edge species. Owing to human dominated ecology it is frequently involved with synthetic man-made structures. As with all bumblebees (of which there are 24 species in the UK) the queens begin the life cycle by executing nest searching flights. For the Tree Bee this takes place in March and April. The nests are usually associated, unusually for bumblebees in general, with vertical surfaces – fences, house walls, bird boxes etc. We are most likely to observe the species from March until July (although occasionally later)

It is a highly active species and an excellent pollinator. All bees are friends to humanity of course – it was estimated by Albert Einstein that if the world bee population were to become extinct, so would the human population only four years later. The varroa mite, problems with pesticides and climate change has resulted in a global decline in the bee population. At Pestcotek we would encourage you to encourage them! If you have located a nest, please bear in mind that it will soon decline and that they will not return to a dead nest the following year.