In mid to late summer, the bumblebee colony reaches peak strength and may contain up to about 100 adult bees. At that time, if the colony is strong enough, the queen will lay some eggs that have not been fertilised. The larvae from these eggs will become male bumblebees. Some of the larvae from fertilised eggs will be given extra food and this enables the resulting adult bees to be queens with functioning ovaries. Mating takes place in late summer, so the overwintered young queens are ready to start reproducing in the following spring. In late summer, the old queen, the workers and the males die, while the young queens burrow into the soil where they overwinter. Common carder bumblebee nests are usually the last to die out, with workers still active in October.
Cuckoo bumblebees do not produce a worker caste
. All of their eggs will develop as larvae that become young queens or males. They do not need worker bumblebees of their own as they exploit those of the host bumblebee species to provide food for the larvae.
In recent years, some queens of some bumblebees, particularly the Buff-tailed bumblebee, have not remained dormant over the winter. They have emerged in winter and have established nests to the extent that some worker bumblebees can be seen collecting nectar and pollen from winter-flowering garden plants, such as Clematis cirrhosa
species. It is doubtful if these winter colonies can survive long enough to rear queens and males. The appearance of winter bumblebee colonies in Britain may be an indication of milder winters resulting from climate change.
Role of bumblebees in gardens
Bumblebees are useful pollinating insects. Although often less numerous than honeybees, bumblebees are more tolerant of cold wet conditions and will visit flowers when honeybees stay in their hives. Colonies of the Buff-tailed bumblebee can be purchased and are used by commercial growers to pollinate glasshouse crops, such as tomatoes and peppers.
Bumblebee tongues are formed from the labium
, supported by the maxillae, and vary in length. Some species are adapted with long tongues to take nectar from deep flowers such as lavender. the Garden bumblebee Bombus hortorum
's tongue is twice as long
as that of Bombus terrestris.
Bumblebee species with short tongues sometimes cheat in order to get at nectar that cannot be reached from the front of the flower. They bite a hole in the base of the flower, which gives them access to the nectar without coming into contact with the pollen-bearing anthers, thus reducing the chances of pollination occurring. Holes made in the base of flowers are often seen on runner bean, broad bean and aquilegia.
Bumblebee nest boxes can be bought from garden centres but they have a notoriously poor success rate in attracting a queen bumblebee in the spring. Queens seem to prefer to find their own, more natural, nest sites. Worker bumblebees can sting but they are generally not aggressive and rarely use their stings unless they are handled clumsily or their nest is under attack. Tree bumblebees are more likely to chase people and sometimes sting them. This is mainly a problem where they are nesting in a bird box which has been placed where people will walk close by.
Other sources of information
Website of the Bumblebee Conservation Trust
Website of the Bees, Wasps and Ants Recording Society
Images and information by Steve Falk
Benton, T. (2006) Bumblebees. Collins New Naturalist series no. 98. Harper Collins
Edwards, M. & Jenner, J. (2009) Field Guide to the Bumblebees of Great Britain and Ireland. Ocelli Ltd
Goulson, D. (2010) Bumblebees, Behaviour, Ecology and Conservation. Oxford University Press
Kirk, W. D. J. & Howes, F. N. (2012) Plants for Bees. International Bee Research Association
Prys-Jones, P. E. & Corbet, S. A (2011) Naturalists' Handbooks 6 Bumblebees. Pelagic Publishing