I’ve been away working for the past 2 weeks with very little time at home to check on what’s happening in the garden. When I got back late the other night I was informed that bees were swarming around a birdbox on the Rowan Tree that we share with the next door neighbor. In fact the tree and the birdbox are theirs, but I’m claiming this one for the garden. The next morning I took a little trip down to have a gander to check it out. There is certainly activity in the birdbox, but not honey bees but the Tree Bumblebee, Bombus hypnorum.
This calls for a small celebration I think. Unlike so many of our bees that have been in decline over the past years, B. hypnorum is expanding throughout the UK. It was first recorded in 2001 from a specimen found on the Hampshire/Wiltshire border. It seemed to stay in this general area for a while, but from 2007 there has been a rapid expansion throughout the England and Wales. Then in 2013 it was recorded in the Lowlands of Scotland, and in Antrim in 2014. B. hypnorum has a natural distribution in Mainland Europe, through Asia and up to the Arctic Circle.
One of the reasons for this rapid expansion could be it’s natural habitat of lowland woodland is pretty widespread, and with the expansion of urban woodland new territories are common. The bees are found in a variety of habitats, from woodlands, roadside verges and scrubby grasslands, to town parks, gardens and allotments. The bees are regularly found visiting flowers of fruit trees and fruit bearing plants such as bramble and raspberry, where they can be effective pollinators and improve crop yield.
B. hypnorum can be identified from the colour patterns (banding) on the thorax and abdomen. The thorax is tawny to reddish brown, the abdomen is black and tail is white. Queens, workers and males (drones) all have a similar colour pattern. Drones are chunky, about twice the size of a honey bee, have blunter ends to their abdomens and noticeably long, curved antennae. Newly hatched drones have a patch of yellowish facial hair, but this wears off with time. Queens vary signicantly in size. Workers are quite small.
This one of the first bumblebee species to be seen in the spring, and are seen from March through to July. In March and April the Queens do “nest searching flights”, looking for somewhere suitable to nest. Colonies are usually located well above ground level. Bird-boxes, containing old bird nests are commonly used. It has been recorded that queens have evicted Blue Tits from a nest box. Other locations they choose to nest are holes in trees and places high up in buildings, such as soffit boxes, under roof tiles and at house eaves. Nests have also been occasionally recorded in the vents from tumble driers, but are usually higher up than this.
Once the nest has been established it takes about six weeks before the workers start foraging. Smaller workers stay at home to tend the nest, and the larger workers undertake all the foraging for the colony. It can be four to five months for the colony to go full-cycle and die out. Colonies can build up to 300 – 400 bees, but most colonies are likely to be smaller. Drones leave the colony and never return, living a self-sufficient life for many weeks while foraging for themselves and looking for opportunities to mate. Colonies often die out early, due to attack by caterpillars of Aphomia sociella Wax Moth (more on this here).
In May, June and July clouds of bees appear to fly around the nest in an aerial dance called ‘nest surveillance’. This is caused by male drones patrolling and waiting for virgin queens to leave the nest so that they can mate. It is thought that drones patrol from nest to nest waiting to mate with the emerging queen. When a virgin queen appears, the drones attempt to mate with her in what looks like a fight. The pair fall to the ground where they can remain coupled for some time. Following mating the queens will forage to build up their body reserves before hibernating over winter to start the process again next year.
Bombus hypnorum. NBN Gateway. https://species.nbnatlas.org/species/NHMSYS0000875501 (accessed 2017.05.27)
Hill, C. (2015) Introducing the ‘Tree Bumblebee’ Bombus hypnorum. https://bumblebeeconservation.org/images/uploads/Tree_bee_article_2015.pdf