Bombus pascuorum, the common carder bee.
Frank Vassen from Brussels, Belgium, CC BY 2.0, via Wikimedia Commons

Bombus pascuorum Scopoli, 1763, the common carder bee, is the ginger bumblebee in the garden from March to October: the one that is still foraging on the ivy and the knapweed long after most other species have finished for the year. It is Britain's only common and widespread all-brown bumblebee, with one of the longest flight seasons of any British bee, and the distinctive habit that gives it its name: gathering, or carding, moss and dry grass to thatch the surface of its above-ground nest. It is widespread across England, Wales, Scotland and Ireland, present in almost every habitat from inner-city gardens to upland grassland, and a key pollinator of long-tubed flowers that shorter-tongued bees cannot easily reach. See where it lives on the UK Native Bee Species Map, or explore its close relatives in the World Bee Atlas.

Taxonomy and Classification

The common carder bee was described by Giovanni Antonio Scopoli in 1763. It belongs to the family Apidae, tribe Bombini, and sits within the subgenus Thoracobombus, a grouping of predominantly brown or tawny bumblebees sometimes called the carder bees.^[1] There are four all-brown bumblebee species recorded in Britain: the common carder bee, the moss carder bee (Bombus muscorum), the brown-banded carder bee (Bombus humilis), and the shrill carder bee (Bombus sylvarum). The latter three are all scarce or declining; B. pascuorum is the only one that is common and widespread, and in parts of northern Britain it appears to be expanding into territory formerly held by B. muscorum.^[2]

Identification

The common carder bee is the only common, widespread all-brown bumblebee in Britain, making it relatively straightforward to place in the field, though pinning down individual specimens to species within the all-brown carder group can be difficult. The key identification feature that separates B. pascuorum from the rarer carder bees is the presence of at least some black hairs scattered among the ginger on the abdomen.^[3] The thorax is a warm ginger-orange in fresh spring bees and fades through the season to a pale buff or straw colour by late summer.

Queens are 16 to 18 mm, distinctly smaller than the queens of many other British bumblebees. Workers range from 10 to 15 mm and can be very small early in the season. Males are 13 to 14 mm with a longer face than other bumblebees, yellow facial hair and some black hairs.^[4] All castes share the all-brown body without the yellow bands seen in Bombus terrestris or the red tail of Bombus lapidarius. The face is distinctly longer than wide, a useful feature if examining a stationary bee closely. It is a long-tongued species, with a tongue that exceeds the sheath, allowing it to reach the nectar of deep tubular flowers that short-tongued bees must bypass.

What "Carder" Means: The Nest-Building Behaviour

The name carder comes from the textile trade. Carding is the process of combing raw fibres into alignment before spinning, and the common carder bee does something visually similar: females gather moss, dry grass and plant fibres, pulling and teasing them into a loose mat that forms the outer covering of the nest.^[1] The result is an above-ground nest tucked into a grass tussock, under a hedgerow or in a pile of plant litter, camouflaged and insulated by this hand-made thatch.

Nests are most often built at or just below ground level in long tussocky grassland, under hedges, or occasionally in nest boxes, wall cavities and old bird nests. A successful nest reaches its peak population of 60 to 150 workers in August, making it smaller than the colonies of Bombus terrestris or B. lapidarius. The average colony lifespan after founding is around 25 weeks, one of the longest of any British bumblebee, consistent with the species' exceptionally extended flight season.^[4]

The Longest Season: March to October

The common carder bee has an exceptionally long flight period, and is possibly bivoltine, producing two generations in a year in favourable conditions in southern Britain.^[3] Hibernating queens begin emerging as early as March, well before most other bumblebee species. Workers appear from April and continue foraging into October, sometimes November during mild autumns. New queens and males emerge from July onwards. In northern Scotland the whole season can be shifted by up to two months later than in the south.

This extended presence is ecologically valuable. The common carder bee bridges early spring and late autumn, providing pollination services in windows that many other species miss. In late summer and early autumn it is frequently the dominant bee on devil's-bit scabious, thistles, knapweeds, ivy, lavender and late-flowering garden plants, continuing to forage in weather and temperatures that would ground most other bees.

Foraging: The Long-Tongue Advantage

Bombus pascuorum is broadly polylectic, visiting a very wide range of flowering plants, but its long tongue gives it access to deep-corolla flowers that shorter-tongued bees cannot easily reach. It shows a preference for pollen from the legume family (Fabaceae), dead-nettles and related plants (Lamiaceae), foxgloves and their relatives (Scrophulariaceae), and red-flowered composites (Asteraceae).^[3]

Regularly visited species include red clover, white clover, bird's-foot trefoil, vetch, comfrey, lavender, bugle, rosemary, woundworts, foxglove, bramble, raspberry, knapweed, devil's-bit scabious, thistles, Himalayan balsam, and buddleia. In spring, queens feed on sallow, blackthorn, bluebell, dead-nettles and ground ivy. The long tongue means the common carder bee is one of the few species able to pollinate red clover effectively, a commercially important forage crop.^[1]

The Field Cuckoo Bee and Other Parasites

The main social parasite of the common carder bee is the field cuckoo bumblebee (Bombus campestris), a wasp-patterned bee that invades established carder bee colonies, kills or subdues the host queen, and uses the existing worker force to raise its own reproductive offspring.^[1] Females of B. campestris are commonly observed near carder bee nests in early summer.

Beyond the cuckoo bee, the common carder bee is also targeted by the conopid fly Sicus ferrugineus, which intercepts foraging workers in flight and lays an egg inside the bee's abdomen. The developing fly larva feeds on the bee's internal organs before emerging. The nematode Sphaerularia bombi parasitises hibernating queens, preventing them from nesting in spring.^[5] These parasites are a natural feature of the ecology, and their presence indicates a healthy population of host bees.

A Bee for Every Month, A Honey for Every Season

The common carder bee is in the garden from the first warm days of March to the last mild days of October. It makes no honey: like all bumblebees, the colony produces only enough nectar stores to last a few days, with nothing to harvest. What it produces instead is pollination, month after month, on the flowers that feed both wild plants and managed crops.

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