The Essex Naturalist 113
B. (Megabombus) hortorum (L.)
Widespread and common with post-1980 records from 50 10km squares in the
county.
B. (Megabombus) ruderatus (Fabricius) - Notable B
A very local and declined species with most modern records confined to
southern England (Falk 1991). There are post-1980 records from only three
10km squares in the county.
B. (Thoracobombus) humilis Illiger
Always local and now much declined with post-1980 records from only three
10km squares in the Thames Estuary where it can still he locally common.
B. (Thoracobombus) muscorum (L.)
Scarce with post-1980 records for only eight 10km squares, mostly in the east of
the county.
B. (Thoracobombus) pascuorum (Scopoli)
A very widely distributed and common bumblebee with post-1980 records from
every 10km square in the county except TR09.
B. (Thoracobombus) ruderarius (Muller)
Appears to he local and much declined in the county with post-1980 records for
only sixteen 10km squares. It could he under-recorded, due to its similarity with
B. lapidarius.
B. (Thoracobombus) sylvarum (L.) - Notable B
A local and much declined species which used to he reasonably common in
southern England (Falk 1991). The Biodiversity Challenge Group has recently
included the bee in the top 100 priority list of species for target action plans in
Great Britain. The only post-1980 records in the county are from two localities
in the East Thames Corridor. These are Ferry Fields (Tilbury), a site threatened
by development and included in the Thurrock Draft Local Plan as Land for New
Development in Primary Areas and Wat Tyler Country Park at Pitsea. There is
an additional possible sighting from the nearby Fobbing Marshes.
Genus: Psithyrus cuckoo bumblebees. Five of the six British species are
recorded for the county and there are recent records for all of these.
Psithyrus barbutellus (Kirby)
A social parasite of Bombus hortorum. Widely distributed in the county with
post-1980 records from nineteen 10km squares.
P. campestris (Panzer)
A social parasite of Bombus pascuorum and possibly B. humilis. Apparently scarce
and local with post-1980 records from ten 10km squares.
P. rupestris (Fabricius) - Notable B
A social parasite of the common and widespread Red-tailed Bumblebee Bombus
lapidarius. The species used to be reasonably common in many parts of southern