Winter active bumblebees
What is a winter-active bumblebee?
Since the 1990s, naturalists have noticed that, rather than hibernating, some bumblebees have been active all winter. Queens and workers have been seen foraging for pollen and nectar from a wide range of winter-flowering plants, and mating pairs have been recorded in February. These have almost all been identified as the Buff-tailed bumblebee (Bombus terrestris) and it is clear that a proportion of queens produced over the summer have begun to establish nests in the autumn instead of going into hibernation.
The Trust are working closely with the national recording body BWARS (Bees, Wasps and Ants Recording Society) to understand more about this behaviour – which species are involved, what’s driving the change, and how are they managing it?
To help, if you see a bumblebee between the 1 November – 1 March, please record it at iRecord. Include as much detail as possible – we’re particularly interested in answering these questions:
- Which species are involved? The Buff-tailed bumblebee is by far the most common, but there are winter records of several other species, though these may just be early-emerging queens.
- Which castes are involved? Queens, workers and males all tell us different things about the state of the colony they have come from
- Where in Britain are bumblebees becoming winter-active? How far north and is this just an urban phenomenon?
- Are the bees collecting pollen from the flowers or just feeding on nectar (or both)?
- Which species of flowers are being visited?
- What weather conditions are best for the bees?
If you do see any winter-active bumblebees it is particularly useful to have a series of repeated observations (e.g. weekly or fortnightly visits in suitable conditions, or a series of observations under varied conditions). This lets us better understand the dynamics of winter-active populations and which weather conditions they can best forage in.
What do we know so far?
Traditionally, hibernating queen bumblebees in the UK would emerge in the spring (roughly March-May depending on species and weather conditions), and establish a nest (in some cases with a partial second generation). As summer fades to autumn, the old queen and all of the workers and males would die off, the new queens would enter hibernation, and from October onwards our skies would be bare of bumblebees.
In recent decades however, this has not always been the case. From the 1990s onwards, bumblebees have been recorded actively flying and foraging through the November-February period. Several species have been reported, although most have been queens in February and are likely to represent queens emerging early from hibernation. For the Buff-tailed bumblebee, however, queens and workers have been seen actively foraging from October right through to March, collecting pollen as well as nectar, and males (and mating pairs) have been seen in early spring. Occasionally, the nests themselves have even been found.
These nests are able to survive on the increasing amount of forage resources available throughout the winter (both non-native plantings such as Mahonia and longer flowering seasons of native plants such as White Dead-nettle). Key flower species seem to be Mahonia (several species and hybrids), Winter-flowering Heather Erica carnea, Winter Honeysuckle Lonicera x purpusii, and Strawberry Tree Arbutus unedo, but foraging has been recorded from a wide range of plant species over the course of the winter. In at least some cases these nests are able to produce new reproductive individuals in spring, so the production of winter colonies is not a dead loss to the population, although it is unclear whether enough colonies survive that
Many of the sightings are in towns and cities. This may be because these tend to remain warmer than the surrounding countryside through the Urban Heat Island effect; alternatively there may be more winter flowers in towns than in the countryside (some non-native species such as Mahonia are common in amenity plantings and in gardens but scarce in wilder areas). It may just be that there are more people in towns so more eyes to spot bumblebees! There are some sightings in the wider countryside, especially along the coast in the south and south-west, but winter-active bumblebees have been recorded as far north as Edinburgh and Dundee.
Wherever you are there’s a chance of seeing a winter-active bumblebee – please do send in any sightings to iRecord.
A scientific article on winter activity and foraging rates of bumblebees was published in 2010 (Stelzer et al) and can be downloaded for free from the journal website. An update is in preparation.
Frequently asked winter bumblebee questions:
