Glow-worms Lampyris noctiluca L. (Coleoptera: Lampyridae) in Essex
occurred in very low abundance. Individuals were observed in greater abundance at sites where
rabbit grazing was evident, particularly on the heathy grassland of Little Baddow Heath (part of the
Danbury Ridge transect).
Discussion
The widespread but localised distribution of L. noctiluca in Essex (Fig. 2) is similar to the national
distribution of this species. In Essex, it would appear that L. noctiluca only occurs where there are
suitable habitats such as unimproved meadow or ancient woodland, which are rare habitats in the
county (Corke 1984). The dearth of favourable areas in Essex explains the localised distribution of
this species. Habitats such as improved pasture may be unfavourable because of low snail
populations, which arc the food source of L. noctiluca larvae. In areas where there arc extensive
patches of suitable habitat such as the large ancient woodlands and meadows of Danbury Ridge,
there are many colonies evident in close proximity.
The fragmentation of suitable habitats and thus isolation of colonies is compounded by the sedentary
nature of this species. The adult females cannot fly to disperse and colonise new areas, whilst the
larvae are not thought to move far in search of food (Tyler 2002). The larvae are reported to move
approximately five metres an hour, but they may find roads or arabic fields a significant barrier to
dispersal. Isolated colonies such as the one in the grounds of Saffron Walden's hospital may
therefore lose genetic diversity and ultimately sustain insufficient individuals to remain viable.
Corke (1984) states that L. noctiluca appears to be rare in Essex, which was seemingly confirmed
by the county recorder having records of only 13 sites. However, with the 2001 survey collating
records from 43 sites since 1992, L. noctiluca is evidently not as rare as was first thought. In
comparison with other counties, Essex has a relatively high number of I. noctiluca colonics. For
example, 58 colonies were recorded in a ten year survey of Gloucestershire from 1980 to 1990,
which is believed to be one of the most favourable counties for this species in Britain due to the
presence of extensive tracts of unimproved limestone grasslands (Alexander 1992).
Despite the relatively high number of Essex colonies, 37% of all of the glowing females which
were observed in the transect survey were recorded within one site (One Tree Hill). Counts were
generally low outside of this site (Fig. 3), so caution must be exercised in declaring L. noctiluca as
'safe1 in a county context. The important colony at One Tree Hill is afforded some protection
because the area is within a Country Park and is therefore regularly monitored. The main threat to
this colony is probably through loss of suitable habitat due to scrub encroachment.
Statistical evidence of declines in L. noctiluca abundance is scarce, but many naturalists believe
that there has been a steady decline in the British population since the 1950s (Tyler 1994).
Throughout the UK, this species has disappeared from many of the sites at which it was once
common and this is reflected in the information collected during this study. Cole (1899) states that
there were many colonies in Epping Forest in the late 1800s and even in the early 1900s, L. noctiluca
was noted as having a patchy distribution within this area (Leutscher 1974). However, there has
only been one observation of L. noctiluca in Epping Forest since 1992 despite extensive searches
within this area during the 2001 survey, therefore leading the authors to believe that L. noctiluca is
currently rare within the forest.
The decline in L. noctiluca abundance within Epping Forest may be attributed both to the reversion
of many of the favourable open grassy areas to woodland and to the close proximity of the forest to
London. Succession has occurred because grazing and traditional woodland management practices
Essex Naturalist (New Series) 19 (2002)
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