The Common Carder Bumblebee, Bombus pascuorum, is the most frequently seen Bumblebee on the reserve at St Nicks, though the Tree Bumblebee, Bombus hypnorum, is rapidly catching it up. Tree Bumblebees first arrived in the south of England in 2001 from continental Europe, and have since spread northwards, reaching Yorkshire in 2010 and Scotland three years later. Happily, unlike some new insect arrivals the Tree Bumblebee is no threat to our native species. It makes its nest in tree cavities or holes in buildings and even bird boxes while most native bumblebees in Britain build their nests on or under the ground. Tree Bumblebees are not aggressive to other species, and are busy and very welcome pollinators.
Common Carder queens are among the first bumblebees to be seen in spring, emerging from hibernation in March and April. To begin with they need to gain strength by nectaring at early flowering plants such as the White Deadnettle. This grows in abundance at St Nicks and can be found in bloom even in winter. Then they get on with searching for a suitable nest site, often in leaf litter at or just below the ground, and start to build their nests.
The nectar and pollen the queen finds in her foraging flights are now brought back to the nest. The pollen is gathered into a lump on which she lays her first eggs and which provides sustenance for the emerging grubs (larvae). She also makes a wax pot in which to store nectar, to feed both herself and her larvae. Like birds, queen bumblebees incubate their eggs, providing well-regulated warmth from their own bodies.
After 4-6 days the eggs hatch, while the larval and pupal stages each last up to two weeks. The young bees which emerge from pupation from late April onwards are at first all females – the workers – which now help their queen to enlarge the nest, protect and feed her, and service the later growing young by bringing back nectar and pollen.
From May onwards a Common Carder bumblebee with full pollen sacs is almost always a female worker, because the queen now mostly stays in the nest and concentrates on laying more eggs and tending the new grubs. She and her workers protect the eggs and larvae by making covering mats of moss and grass with their legs. This activity is similar to carding wool, hence the family name to which the Common Carder belongs.
As the season progresses and the colony has grown to between 50 and 200 bees, provision for the future becames a priority. The queen starts to lay unfertilised eggs which will grow into drones (males) whose sole purpose is to mate with and fertilise late-emerging female bees, who if they survive the winter and predators will become next year’s queens.
With the onset of autumn the colony’s task is complete. The old queen dies, as do her workers and males, leaving the new young queens to visit late summer flowers and build up extra strength to enable them to live through the winter ahead. When ready they search for a protected place to hibernate (in insects hibernation is called diapause) and here they stay until the following spring when increasing day length and growing warmth provide the wake-up call to start new colonies.
Until the arrival of the Tree Bumblebee the Carder Bumblebees were the only British species to be recognised by the gingery fur-like coat on the thorax. The Tree Bumblebee also has a furry ginger thorax, but its abdomen is black apart from a thin white tail. The Common Carder’s abdomen has thin black-and-white bands (sometimes faint), but as the season progresses this and the ginger thorax frequently fade to a drab mottled pale colour. Their small size and nondescript appearance, unlike other bumblebee species, means they are still easily recognisable as Common Carders. The species is common and widespread in the British Isles, found from Land’s End to the Orkney Isles. These busy pollinators are an important and valuable part of the St Nicks ecosystem.