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The Moss Carder Bee (Bombus muscorum)

Tom Gittings

Ecological Consultant
The Moss Carder or Large Carder Bee (Bombus muscorum) is a distinctive bumblebee that can be easily identified in the field (in Ireland) by its orange thorax and ginger abdomen without any black hairs. The more frequently encountered Common Carder Bee (Bombus pascuorum) is similar in general appearance but has variable amounts of black hairs on the upper abdominal segments. Unlike other familiar bumblebees, which nest underground, carder bees nest above ground, covering their nests with moss and dry grass. The name carder refers to their habit of combing material together (carding) to create this covering. The Moss Carder Bee is classified as near-threatened in the Regional Red List of Irish Bees and is a Priority Species in Northern Ireland. It requires flower-rich habitats and it is largely absent from lowland agricultural landscapes. This is reflected in its Irish distribution, which is concentrated around the coastline with inland records mainly from areas with extensive semi-natural habitats such as the Burren and the midland bogs. In East Cork, it occurs extensively along the coastline from Roches Point to Youghal, where coastal grasslands and heathlands, sand dunes, eroding sedimentary cliffs (soft cliffs) and strandline vegetation provide suitable flower-rich habitats. The map shows the distribution of recent (post-2005) 1 km square records in East Cork. The concentration of records between Roches Point and Ballyrobin reflects my survey effort and, based on the distribution of suitable habitat, it is likely that this bee has an almost continuous distribution along the coastline between Roches Point and Youghal. However, there may be some gaps in this distribution: for example, along the Ballycotton Cliff Walk the uncultivated coastal fringe is mainly overgrown with bramble, bracken and gorse. In a survey of the cliff walk, I only recorded this bee in a section that had been recently burned, providing suitable flower-rich habitat before the regenerating vegetation became scrubbed over. It is rarely found away from the coast in East Cork: my inland records come from two limestone quarries in the vicinity of Cork Harbour, Mitchell’s Wood (near Castlemartyr) and two upland areas with patches of Molinia meadow and heath habitat. Bumblebees are known to be able to travel several kilometres from their nest whilst foraging. However, the Moss Carder Bee appears to be less mobile compared to other species: a German study found that 65% of observations of marked bees of this species were within 100 m of their nest, with the maximum distance recorded being only 125 m, while 45% and 87% of the observations of the other two bee species studied (Bombus lapidarius and Bombus terrestris) were over 500 m from their nests. Genetic studies indicate that the Moss Carder Bee has low dispersal ability and reduced genetic diversity due to inbreeding with inbreeding causing high levels of sterile triploid bees. It is suggested that populations require at least 15 km2 of suitable habitat to avoid inbreeding problems. This has implications for the inland populations in East Cork, which are unlikely to have anywhere near that level of suitable habitat available. The low mobility of this bee is illustrated at Roches Point where it shows strong fidelity to its favoured habitats: it occurs along the seaward shoreline west of the lighthouse  where flower-rich vegetation has developed on the eroding cliffs, but rarely visits the west-facing beach north of the lighthouse or the gardens of the Coastguard Cottages. The Moss Carder Bee is described as favouring Fabacae (vetches and clovers), Scrophulariacae (figworts), Lamiaceae (mints and deadnetttles) and red-flowered Asteraceae (daisies, etc.) flowers. In East Cork coastal cliff and grassland habitats, Kidney Vetch (Anthyllis vulneraria) is the predominant flower visited in spring and early summer. However, this may simply reflect the fact that it is the most abundant flower in the habitats favoured by the bee at this time. Other flowers commonly visited in East Cork include Bell Heather (Erica cinerea), Sheepsbit (Jasione montana) and Sea Mayweed (Tripleurospermum maritimum). The Moss Carder Bee is a distinctive species that can be identified in the field. There are guides to the identification  of Irish bumblebees available at the NBDC website as well as an Android app. Please submit any records to the  National Biodiversity Data Centre, via the online submission form or the Android app. 
Bombus muscorum habitat at Roches Point