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narrower in hortorum). A good character for identification is that the males of ruderatus have a
reddish 'beard' in the mandibles, whereas Illis is black in hortorum.
This species may be under-recorded on account of its similarity to hortorum. However, it has
declined rapidly nationally, and has been recorded in Essex on exceedingly rare occasions since
1980. Whilst it is possible that populations of this species still survive in the county, the
evidence at the moment suggests it is either extinct or very close to it. A thorough survey of
suburban gardens could well provide valuable evidence on this.
Bombus humilis (Illiger) Plate 1
This species is very similar to Bombus pascuorum, its close relative. The females have yellowish
to ginger-brown ground colour, with a darker brown band on segment two of the abdomen. In
contrast to B. pascuorum there are no black hairs on segments one to five of the abdomen.
Careful examination with a lens of the front and sides of the abdomen is necesary to distinguish
this species from pale examples of pascuorum. Useful features for distinguishing this species
from Bombus muscorum include the presence of small numbers of black hairs, especially around
the wing-bases, on the thorax of humilis (no black hairs in muscorum), and the hairs at the side
of the third abdominal segment emerging from small pits in humilis, and from tiny 'bumps' in
muscorum. However, some Essex specimens of humilis have no discernable black hairs on the
thorax, the pits/bumps distinction requires a microscope, and is even then clearly observable
only in queens! For really definitive identification it is unfortunately necessary to dissect out
either sting-sheaths or male genitalia.
Queens are said to emerge from hibernation rather later than those of the commoner species, and
active workers can be seen correspondingly later in the season. Bombus humilis is included in
the U.K. Biodiversity Action Plan on account of its recent rapid decline in the U.K. In Essex it
appears to be confined to a scattering of sites along the Thames estuary. These include
remaining grazing marshes and sea-walls, disused quarries and other 'brown-field' sites,
roadside verges, country parks and so-called 'waste ground'. Although the species is common in
many of these habitats, the whole area is subject to intense 'development' pressures, which also
affect other rare and threatened Aculeates (see Peter Harvey 1997).
Bombus muscorum (Linnaeus)
As noted above, this species is very similar to both Bombus pascuorum and humilis. The lack of
black hairs on the thorax and on segments one to five of the abdomen are useful identifying
features. It also has a 'smart' cru-cut appearance owing to the evenness of the length of the hairs
on its body. In Essex it appears to be confined to the remaining grazing marshes and sea-walls
on the coast, in scattered populations from Foulness in the south to Dovercourt in the north.
However, these populations are very small, and some appear to have become extinct quite
recently, possibly due to sea-wall maintenance. Despite the similar habitats occupied by humilis
and muscorum, their Essex distributions seem to be entirely distinct. This species appears to be
one of the most threatened of the Essex species, and research for active conservation is urgently
required.
Bombus ruderarius (Muller)
This species was always somewhat local, but now seems to be in rapid decline nationally. The
females are similar in general appearance to those of Bombus lapidarius, being mainly black,
with a red 'tail'. This similarily may be responsible for some degree of under-recording of
ruderarius, but there is little doubt that it is much less common than lapidarius and the other
Essex Naturalist (New Series) 16 (1999)