I’ve always been bewildered by the number of different, yet very similar looking, bumblebees around my garden, writes Ann Chilcott, Scottish Expert Beemaster.

Their identification challenges me so I am investigating this species further in order to share some information with you over a series of articles. I will examine the life cycle, identification, pressures on species, and what we can do to improve and sustain bumblebee numbers in the UK.

Red-tailed Bumblebee (Bombus lapidarius) on Bramble.

Photo: Ann Chilcott

Confounding identification is the fact that there are around 250 species of bee in the UK including the honey bee, 24 species of bumblebees, and 225 species of solitary bees. If that’s not enough, some cuckoo bees masquerade as bumblebees killing their queens, usurping their nests and fooling their workers into raising cuckoo bee offspring as their own. Some hoverfly species impersonate wasps and honey bees so all is not always as it seems in the insect world.

Bumblebees are large fuzzy insects closely related to honey bees and they share the following scientific classifications: Class: insects; Order: hymenoptera (membrane- winged); Family: apidae. However, honey bees are in the Genus Apis whereas bumble bees are in the Genus Bombus. Using the Latinised scientific binomial classification system avoids further confusion given that one bumblebee, Bombus terrestris, is known by several common names around the country including Large Earth Humble-bee, Buff-tailed Humble-bee and Buff-tailed Bumblebee.

Bumblebees look like big friendly teddy bears with their round fluffy bodies covered in soft hairs called setae that pick-up pollen. However, most bumblebee species have pollen baskets on their legs. Cuckoo bumblebees are the exception because they steal the food of others and so don’t need shopping baskets.

You might almost imagine friendly bumblebees rolling over defencelessly on their backs like dogs wanting to be tickled. However, the brightly coloured body bands that help us identify bumblebees also act to scare off animals. This is known as aposematism and functions as a warning to predators, so a brightly coloured ball of bees might put off marauding predators such as birds. Female bumblebees have a painful sting which I know about because I once rescued one in a tissue. I didn’t have a glass tumbler to hand to place over it on the window and so wasn’t able to safely slide a sheet of paper between the tumbler and window thus keeping my distance from the stinging end. Ouch!

Common Carder bee nest, Bombus pascuorum.

Photo: Raymond Hutcheon

Bumblebee sub-species have varying lengths of tongues ranging from 7.1mm in B. pratorum to 13.5 mm in B. hortorum which means that they can access flowers with differing lengths of tubes leading to the nectaries. Some short-tongued bumblebees tear holes in the base of the flower to rob nectar and honey bees sometimes take advantage of this strategy to help themselves. Bell heather is a good example and I have found flowers on a stem with a hole in each bell which actually consists of 9 fused petals. Honey bees can access the nectar by probing inside the flower but they find it so much easier to steal instead.

The proboscis is hard, long, tapered and designed to fold away neatly and invisibly under the neck when not in use. When in use it forms a straw-like structure where fluid is lapped up and rises up the tube in a capillary-like action. Interestingly, honey bees have very similarly structured proboscises but just slightly shorter and their lengths range across the sub-species from 5.7-6.4mm in the British Black Bee (Apis mellifera mellifera) to 6.4- 6.8mm in the Carniolan Bee (Apis mellifera carnica).

Red-tailed bumblebee (Bombus lapidarius) nest - many have hatched. Photo: Tyrone Williams 

True bumblebees, also known as social insects, have pollen baskets (at least the two female castes do) which distinguishes them from kleptoparasitic cuckoo bumblebees who have none but mimic bumblebees in order to steal their nests and resources. Social insects have a dominant and reproductive female called the queen, and another female caste called the worker whose sole function is to forage and feed the colony. Social insects care for their offspring in colonies. Males are produced later in the season with mating and passing on their genes being their main functions. However, there is great competition and usually only 1 in 7 males actually mate with a queen. The queen usually mates with only one male unlike the honey bee queen that can have between 7-17 successful suitors.

When males emerge from their natal cells they spend only a few days in the nest where they do no work at all. They then go off and forage for themselves and can often be seen sheltering from rain under a flower head where they may also have sleep-overs when darkness falls. Unlike honey bee males, bumblebee males do not die during mating. They use a scented attractant pheromone to lure the female to a rock or piece of ground and mating may last from 10-80 minutes, usually taking place on or near floor level unlike airborne honey bee mating. After inserting sperm into the female genital opening the male will follow this with a sticky material that hardens to plug the opening preventing other males from mating for at least three days. This strategy ensures that his genes are passed on successfully.

Bumblebee life cycle from Xerces

The life cycle illustration above shows:

1. The queen bumblebee at the of summer finding an underground cavity where she will overwinter by herself, the males and female workers having all died off after fulfilling their roles during one short season.

2. The fertilised queen emerging during spring when her first responsibility is to replenish her own depleted body through adequate nutrition. Over winter hibernation she has lost most of her body fats and so soon as possible must collect pollen to restore protein levels needed for tissue growth, especially for her developing ovaries. Nectar collection ensures that she has enough energy and minerals to function efficiently. Bumblebee queens differ from honey bee queens in that the latter have no pollen baskets and don’t forage.

3. The queen finding a suitable nest and stocking the larder with honey pots. The spring nest site is pretty crucial and it must be well insulated and cosy. Old mouse nests are ideal homes and they can be above ground surface or below depending on the species of bee. Once satisfied with her new home the queen secretes wax from the wax glands on her underside and forms little honey pots which she will fill with nectar to sustain her as she lays eggs and incubates them, and perhaps during some harsh spring weather when confined indoors. She then collects pollen and forms a large lump not much bigger than her own body. On this bed she lays a few eggs which will hatch into larvae to become the first workers. To speed up the development process the queen lies over the pollen bed to incubate her brood. If heat is needed she isometrically contracts her flight muscles to generate more heat and every so often she leans over and sips from the honey pots gaining calories and energy to fuel this process. Like honey bee larvae, bumblebee larvae undergo a few moults then develop a silken cocoon and progress through a pupation period. When the first workers emerge from their cocoons it takes around 24 hours for their wings to harden and then they go straight on outdoors to foraging duties, unlike the honey bee that spends three weeks indoors on household duties before foraging.

4. The male emerging and mating as previously described which completes the life cycle at the end of summer as males, female workers and old queens die leaving only newly mated queens to begin hibernation and start the new cycle of bumblebee life.


This article was written exclusively for Smallholder magazine. For more expertise from Ann Chilcott, Scottish Expert Beemaster, subscribe to the monthly magazine by calling 01778 392011 or emailing subscriptions@warnersgroup.co.uk. It is also available from newsagents.