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.