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Stag
Beetle
Lucanus
cervus
.jpg)
(Photo:
Wildlife Trust)
1.
Introduction
1.1
Biology
Identification
At
an impressive and conspicuous five centimetres in length from tip
of mandible to tip of abdomen, male specimens of this dark brown
and black beetle have been recorded as the largest native terrestrial
beetle found in Great Britain. Physical size and the magnificently
antlered mandibles are therefore a good guide to the identification
of this species when specimens are of this gender, although the
female is only around three and a half centimetres in length with
much smaller mandibles.
The
size of both sexes varies considerably, such variety amongst other
wood-boring insects being normal due to differences in the nutritive
properties of the various trees upon which larvae feed (Imms, 1971).
Life-cycle
Adult
L. cervus may hibernate, as they have been discovered below ground
level during March, although several more months pass by before
beetles are generally observed on the surface. The mature stage
is mainly seen from mid May to early August, although they have
been observed foraging during every week from early May to early
October.
The
beetle feeds on fruit and tree exudates, and most often come to
notice during the day when wandering on the ground. It takes flight
at dusk, preferring warm and windless conditions in which to become
airborne, when males seek out females with which to mate. The resultant
eggs are laid in decaying wood.
Larvae
Requirements
Larvae
are gregarious and generally take around four years to fully develop.
A life-cycle of up to seven years has been mentioned by some but,
as with the size of the adult, the length of time spent at this
early stage of development is probably dictated by the differing
quality of the nutritive input. Grubs usually inhabit the decomposing
deep roots and stumps of a wide range of mature deciduous trees,
sometimes long-dead fallen timber or fence posts down to around
3" in diameter, and occasionally even large heaps of old sawdust.
It
has been traditionally thought that this species only lives in deciduous
timber (UK Biodiversity Group, c.1996) but there are records of
the species utilising the remains of evergreen trees. Larvae bore
fantastical architecture in chestnut fence-posts, and rotting elm,
oak, poplar, willow, birch, Monterey cypress, and holly, these being
the only trees known to have hosted the early stages of this beetle
in Sussex - although a number of other susceptible tree species
will have gone unlisted.
Habitat
Association
The
beetle shows little willful favour towards any particular type of
habitat in Sussex so long as rotting tree-stumps are present in
a comparatively dry and sheltered district, although dense dark
woodland may be avoided. There is no doubt that the insect is extremely
local in its numbered habits, larvae often being confined to one
particular tree-stump within a district. Beetles are therefore only
sporadic in appearance away from breeding sites. On the other hand,
a recent national survey of the species was a great success in Sussex,
as more than 500 individual records were collated during one year
of public observation from about 60 different 2 kilometre squares.
1.2
Current Status
·
Listed on Annex II of the EC Habitats Directive.
· Listed on Appendix III of Berne Convention
· Listed on Schedule 5, Section 9 of the Wildlife and Countryside
Act.
· UK Biodiversity Steering Group Priority Species.
· Nationally Scarce category B.
Europe
L.
cervus is widespread on the continent, and in most countries this
insect is protected by statute. However, the beetle is under no
immediate threat on the European mainland, although the stag beetle
has almost disappeared from a few northern states.
UK
Here
in Great Britain, as early as 1941 it was realised that this enigmatic
insect held a restricted and discontinuous range, and explanations
were being sought. Since that time it has been consistently been
listed as a national rarity, although its status as a rarity has
been questioned recently. The stag beetle's distribution in the
UK is concentrated in the south-east.
In
about 1960 an organised survey was undertaken, when many important
records were gathered and eventually published. Then, as a result
of the United Nations Conference on the Environment and Development
held in Rio de Janeiro in 1992, L. cervus was included on the UK
Biodiversity Steering Group's lists of threatened and declining
species, and was deemed a priority for action. Six years later another
national survey of L. cervus was performed, when the profile of
the insect was raised, many new facts learnt, and important leads
were uncovered in the hunt to unravel little-understood aspects
of its biology. This was an exceptionally well-supported survey
which proved that the species is currently densely distributed in
three main zones in this country - from southern Hampshire to mid
Sussex, in parts of Greater London, Surrey, and Berkshire, and in
Suffolk - and less so elsewhere in the south.
Sussex
The
complete history of the stag beetle in Sussex has been published
in detail, where all known sightings are represented and the most
important records are individually referenced (Pratt, 2000). In
summary of the first 100 years of local entomological recording,
up until the middle of the 20th century the beetle's range extended
as far east as Ringmer and Eastbourne. Only three colonies had ever
been detected in the north of the county, these being the most southerly
of the largest national area for L. cervus which encompassed Surrey
and London, and which were isolated from the main Sussex settlements.
It is also noteworthy that after 1905 no East Sussex records are
known to have been made for half a century. Still, encounters at
Knepp Castle and Battle in 1957 signaled that an unprecedented increase
in territory was under way - sourced from the main swathe of traditional
colonies situated in the south-west - towards the north and well
into the previously completely barren far east.
L.
cervus is under no significant new threat and is not endangered
in Sussex. In fact the species has been gradually extending its
empire here for at least half a century, its current range now far
exceeding that ever recorded within the last 150 years.
The
insect is currently well distributed in much of West Sussex and
around Ringmer, and less so elsewhere; its local range is discontinuous,
being distinctly and characteristically patchy throughout. The mid
20th century colonising push towards the north finally reached the
Surrey border near Haslemere by the late 1990's and is now poised
to reach Tunbridge Wells in Kent, although the early thrust towards
the far east of the county seems to have stalled at Battle. Starting
from an historical baseline of around 15%, the insect's range now
extends to more than three-quarters of the area of Sussex in widely
varying densities of distribution. Around one hundred of the county's
two-kilometre squares boast records of this species, some holding
multiple colonies - but the dichotomy in the general density of
distribution between west and east remains. Whether this expansion
is due to an increase in the recording of this species or a true
increase is as yet unknown.
Despite
the great change in distribution, there is no evidence that the
numerical strength of individual colonies has altered within entomologically
historical times - that is, during the past 150 years. Adults are
still generally casually encountered in singletons, either roaming
by day or more occasionally at night where tungsten light illuminates
domestic windows or in mercury vapour sourced moth-traps. But some
colonies situated in traditional geographical hot-spots, such as
near Shoreham and in Chichester, regularly produce much higher numbers
of beetles. Larvae are quite common in particular tree-stumps throughout
it's range, levels ranging from half a dozen to a dozen grubs per
tree-stump - although as many as 50 have been counted.
2. Current Factors Affecting the
Species[top]
2.1
Climate and Habitat Availability
The stag beetle has always held a patchy distribution and a restricted
range in Sussex. The fastidious insect's failure to colonise some
wind-blasted districts within its normal range, totaling up to 6%
of the vice-counties, is due to an insufficiency of its tree-associated
food - but it is climate that has overwhelmingly dictated this insect's
local distribution and territorial limits (Pratt, 2000). In East
and West Sussex the beetle is almost exclusively found in low-lying
areas where rainfall does not consistently exceed 900 millimetres
per annum, and where it prefers the quickest-draining of all soils.
A shortage of trees and the consistent presence of high rainfall
precisely account for the uncolonised patches within the species
overall range, this cumulatively amounting to perhaps 15% of the
county.
While
high rainfall and treeless downland explain the barren areas within
the beetle's local range, they do not explain just why the insect
increased its territory towards the Surrey and Kent borders during
the last half of the 20th century. But a comparison of the timing
of above average long-term annual temperatures and the pioneering
L. cervus records does show a good agreement - during advantageous
climatic sequences the insect proceeded to colonise northern areas
at a rate of around half a mile per annum.
2.2
Habitat Loss
A whole series of reasons have been proposed to explain this beetle's
patchy and restricted national distribution, and the perception
of fluctuating numbers and territorial decline. Almost all conservationists
believe that by far the main threat facing L. cervus is the removal
of fallen timber and the grubbing up of tree stumps, along with
general habitat loss. It is certainly true that a few Sussex colonies
are physically destroyed annually - but, however deplorable, the
losses are peripheral and are quickly replaced naturally.
It
has also been said that the results of Dutch elm disease and serious
storms have made a positive contribution to this insect's welfare,
but there is no evidence or likelihood that the range or numbers
of L. cervus had been previously restricted by a shortage of rotting
wood in any area away from the East Sussex downs.
2.3
Predation
Other listed threats are cats and pedestrians in towns, and birds,
foxes, frogs, squirrels, automobiles, open water, lawnmowers, and
collectors, elsewhere. However, few of these perceived endangerments
bear much scrutiny as reasons for a serious reduction in the potential
modern-day status of this beetle in Sussex, and all have been dismissed
as numerically irrelevant (Pratt, 2000).
However,
large-sized bats - probably the Noctule, Serotine, or Greater Horseshoe
(M. Love) - do significantly attenuate adult levels annually in
some colonies. For example, about two dozen dismembered bodies were
collected from a lawn at Lancing College during one morning in 1995,
and the beetle was culled nightly, every summer for a decade following
the mid 1970's, by bats at Lodge Hill, Coldwaltham, where up to
10 carapaces could be gathered each morning. During the same era,
similar records were made under lamp-posts at Midhurst.
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