This week I saw my first bumblebee of the year. Gorgeously big and black, with honey-coloured stripes, she was a buff-tailed bumblebee (Bombus terrestris), one of the most common here. All the large bumblebees which appear in early Spring are queens. Hatched last summer, they have spent the winter in hibernation. Even the slightest warmth in the sun summons them forth to fly and feed. Pussy willow, primroses, crocus and the tiny bellflowers of heather are all vital sources of nectar, and the bumblebees’ size and furry coat mean they can exploit these early flowers when the weather is still too cool for other insects to be on the wing.
As the queen fattens, her eggs begin to develop. She seeks out a nest-site – often an abandoned mouse hole or rabbit stop – and it is this which leads to the bumblebees’ characteristic Spring behaviour, when they can be seen flying low and slowly over the ground or climbing ponderously through the plants on a lane-side bank. Many bumblebees are ground-nesting, although some species nest in trees and others will find a way into a roof space or wall cavity and build a nest there. The nest is begun with a ball of moss, grass, feathers or hair (often material left behind by the hole’s original occupant). At the heart of this balled material, the queen constructs a cup of wax, which she fills with nectar-honey, and a wax-coated ball of pollen into which she lays her eggs. These eggs are fertilised as they are laid, with sperm implanted within her by a single male the previous summer. The queen incubates the eggs, shivering her body to keep their temperature constant. She feeds on the nearby pot of honey for the energy to do this, only leaving the nest to gather more nectar when she absolutely must.
When the larvae hatch they feed on the pollen which surrounds them and grow rapidly. To turn from grubs to bees they must pupate in cocoons of silk. As soon as that stage is reached, the queen – who has been adding more pollen all the while – lays her next clutch of eggs, and these will be hatched by the time the first adult bees emerge from their cocoons. These daughters (they are all female) take on the feeding of the second batch of grubs and, with her daughters fully-developed and able to forage for pollen and nectar, the queen now remains in the nest all the time, laying more eggs and relying on her workers for food. A bumblebee nest does not have a honeycomb, being simply a collection of wax honey pots, but quickly becomes larger, so long as food is plentiful, and may contain several hundred females by July.
With the nest at capacity, the development of new larvae alters. Some continue to grow as females, becoming larger future queens, while others develop as males for the first time. Many of the large numbers of bumblebees seen on late summer flowers, such as the blue globe thistle Echinops, may be males, but no matter how much they feed they will not be able to hibernate over winter. Their only purpose was to mate with next year’s queens.
It is unusual to see any queen bumblebees at this time – mated almost as soon as they leave the nest, the new queens will already have gone into hibernation, choosing to dig into loose soil or friable compost heaps, just a little way below the surface. The old queen and her sterile workers have fulfilled their purpose and do not survive into Autumn.
Bumblebees are reluctant to sting – although they can without dying (unlike honeybees) they will do so only if provoked. Unfortunately, one of their best-known predators, the badger, is impervious to this defence. Badgers will even dig out wasps’ nests, so a bumblebee nest in a grassy bank presents no challenge. It is sometimes possible to come upon the dug-out nest the next day, and see straggler workers crawling confusedly upon the rubble of their home. Great tits are known to predate bumblebees, too, picking them from the blossom of flowering trees, such as the tall limes, in large numbers.
But by far the biggest threat to bumblebees is loss of habitat and food sources. For many bumblebees, particularly the rarer, long-tongued species, food means clover and other legumes – the vetches and bird’s-foot-trefoil we call ‘eggs and bacon’ – which once grew so profusely in the flower-rich meadows destroyed by agriculture since the Second World War. That is why it is so vital to fill our gardens with nectar-rich flowers, to welcome the spread of clover in our lawns, and to leave patches or margins of flowering clover and other wildflowers when we mow our lawns or strim our banks. Many summer bedding plants are useless to all bees, with impenetrable double forms and sterile F1 hybrids devoid of pollen. All too often, ‘Best Kept’ and ‘Blooming’ village competitions are the exact opposite of what bumblebees need. Old-fashioned cottage garden plants – the kinds our forefathers grew – are much better. Thyme, lavender and rosemary bushes will often be (almost literally) swarming with hungry workers, and the flower-spikes of Stachys byzantina or Lamb’s Ear, so often cut off in favour of the soft, grey leaves, are always crowded with bees. For more, visit the website of the Bumblebee Conservation Trust at http://bumblebeeconservation.org/get-involved/gardening-for-bees/.
A busy bumblebee passing diligently from flower to flower on a tall spike of foxglove or lupin is a sight we can all enjoy when summer comes round once more, and it was a joy to spot that first queen on the heather this week.
© New Moons For Old, 2015.
Picture credit: Buff-tailed bumblebee in a purple crocus, via Wellcome Collection
For additional information on the bumblebee life cycle, I am indebted to ‘A Sting in the Tale’ by Dave Coulson, founder of the Bumblebee Conservation Trust (published by Jonathan Cape, 2013).