9 for 90: White-tailed Bumblebee

by Nick Acheson
Each of our Norfolk Wildlife Trust 9 for 90 species represents a Norfolk landscape in which we work. Most represent semi-wild landscapes, where natural forces and human management have conspired to give home to a particular flora and fauna. Most of the 9 for 90 are therefore rare specialities: cranes in the wild marshes of the Upper Thurne, early purple orchids in the understorey of North Norfolk’s ancient woods, water voles in the restored wetlands of the Wissey. But for many of us, those who don’t stalk rare species, such precious creatures might just as well be unicorns. One 9 for 90 species, however, is everyday, known by everyone, found everywhere. Representing garden wildlife and urban wildlife that is accessible to everyone, it is the white-tailed bumblebee.

Drop whatever you are doing and focus for a moment on bumblebees; for the lives of bumblebees are astonishing

Bumblebees are all around us; yet most of us know little about their lives. Drop whatever you are doing and focus for a moment on bumblebees; for the lives of bumblebees are astonishing. Though exceptions are possible (UK bumblebee biology seems to be changing in response to generally milder winters) only young queen bumblebees overwinter. Unlike honeybees, bumblebee colonies, and their founder queens with them, die in autumn. The round, fat bumblebees you see emerging in late winter are young queens and they are – quite literally – fat, as their food source through the winter has been fat which they laid down while feeding late last summer.

The job of an emerging queen in early spring is to found a colony. She has no need of a mate as she mated last autumn and has stored the now-dead male’s sperm all winter. Her nest site will depend on her species. Of our six common bumblebee species, three – white-tailed, buff-tailed and red-tailed – favour small underground cavities such as mouse burrows, while the other three – early (or meadow), garden and common carder – prefer the base of a thick tussock of grass.

Once she has found the right site, the queen will spring-clean it, then form a pollen cup. She makes this from wax which she exudes from between the segments of her abdomen and shapes with her mouthparts and forelegs. She fills the cup with pollen gathered from early spring flowers, which she has carried to the nest in her corbicula or pollen baskets on the outer face of her hind tibia. On the pollen mass she lays her first half-dozen eggs. It is still early spring, so to help her eggs to develop she incubates them, sitting over them just like a chicken.

A few days later her first grubs hatch and begin to feed on the pollen she has amassed. They are females, destined to be workers (all of which are female), and they will help raise successive broods. Slowly in this way the colony grows. Later in the summer the queen produces male offspring by not releasing sperm (still from last year’s mating) when she lays her eggs. Unfertilised eggs necessarily hatch as males. Though the mechanism is still poorly understood, the queen’s dominant behaviour and her pheromones are thought to prevent the reproductive development of her daughters, the colony’s workers. As the colony ages and grows, however, the queen’s grip loosens and her daughters begin to lay their own eggs (which she will eat if she finds them). These, being unfertilised, will become males.

Photo by Melissa Minter

How queens regulate the production of new queens is still less understood. Come late summer, however, new queens emerge. To entice them to mate, young males fly in circuits, often many males of various species on the same circuit, leaving scent markers on vegetation as they go. Females find the right scent markers both because each species’ pheromones are distinct and because each species of male flies at a different height from the ground. The scent markers stop females of the right species in their tracks and they are mated by a passing male.

Once a young queen has been chemically lured into mating she leaves her natal nest. Now she must feed for the rest of summer and autumn, to fatten up for her hibernation. She must also find a hibernation site, a hole in a bank, usually north-facing to avoid being woken too early by the first sunshine of the following year.

The six common bumblebees listed above were indeed Norfolk’s six common bumblebees until very recently. This is normally the point in the story where you’re told that tragically one of them has become perilously rare as a result of human carelessness. But no! Although several Norfolk bumblebees have indeed become very rare over the past century, we have, quite remarkably, gained a new bumblebee in the last few years and in no time it has become extremely common. Enter the tree bumblebee, known to aficionados as Bombus hypnorum. First recorded in the UK in 2001, by 2008 the tree bumblebee had reached Norfolk and within a couple of years it was widespread. Today it is possibly the most noticed bumblebee in Norfolk as, thanks to its liking for tree holes, in urban settings it commonly takes up home in garden birdboxes or under the eaves of houses.

As if all that weren’t gripping enough, there is another plot twist, worthy of Rob and Helen in the Archers or of the darkest Jacobean drama. Mated female cuckoo bees, of which there are several species in Norfolk, emerge from hibernation much later than queens of other bumblebees. After all, why waste energy making a nest and raising worker females when you can co-opt the nests and workers of another species? The clue is in the name: female cuckoo bees enter the nest of a host and recycle the wax and pollen to make a basket in which to lay their own eggs (each cuckoo species specialising in the nest of a specific bumblebee). These are then raised, just as a cuckoo is raised by a meadow pipit or a reed warbler, by the workers of the host nest. One species, the vestal cuckoo bee which parasitises the nests of buff-tailed bumblebees, is commonly seen in summer in Norfolk, in diverse habitats including suburban gardens.

Yes, all this drama is happening wherever you see bumblebees. By the river the brambles in delicate pink flower hum with bumblebees. The blazing municipal bedding plants outside the library and on the roundabouts are visited by bumblebees too. Some of these bees are the workers described above, raising their sisters, laying surreptitious eggs out of the way of their mothers; others are young males, planting pheromone trails for unmated young queens; still others are those very young queens, following the pheromones, feeding to survive the winter and found next year’s colonies.

There are rare species of bumblebee of course, many of which have declined dramatically in recent decades as our management of the landscape has become ever more ruthless, more chemical, more mechanical. Yet the virtue of the everyday white-tailed bumblebee, the jolly species every child would illustrate if given a crayon, is that it is commonplace. It is not the musk carder bee of wild dunes on the coast, nor the heath bumblebee which loves the heathers of our Ice Age moraines. It is the happy bumblebee of the urban garden, the buzzing background to summer days outdoors across the county.

Photo by Tom Marshall

Therein lies its importance. Bumblebees are the people’s wildlife. It has never been more important for people to experience bumblebees, and the host of other species which live beside us in our towns, cities and gardens. On the one hand, evidence is mounting that humans are happiest, healthiest and most productive when they have access to green space and green time. This makes intuitive sense: we are a natural species too, and until very recently our society depended on an intimate relationship with nature for food, shelter and survival. Now science is demonstrating that this intuition is correct.

Daily contact with nature, with bumblebees, with woodlice, with gulls pattering on a football pitch, with ivy-leaved trefoil tumbling from a wall, is also essential because nature, more than ever before, needs us. Nature reserves across the county, across the country, which shelter rare species — the crane, the early purple orchid, the water vole — depend on support from us all. The Living Landscapes Norfolk Wildlife Trust is striving to foster depend on everyone’s support too. To remind us daily of these rare species and habitats which must at all costs be protected, we need widespread, commonplace wildlife in our lives. We need the cheery white-tailed bumblebee of our gardens, parks and riverbanks: as fine a symbol as any for our everyday, urban, accessible wildlife and the link it offers to the wonderful wildness of Norfolk.