Species Action Plan
THE SILVER-STUDDED BLUE
Plebejus argus
JUNE 1996
Compiled by:
N.O.M.Ravenscroft and M.S.Warren
Butterfly Conservation
P.O.Box 444
Wareham
Dorset
BH20 5YA
Tel: 01929 400209
This species action plan is an unpublished working document produced by Butterfly
Conservation to focus and co-ordinate the conservation of the Silver-studded Blue in the UK
over the next five to ten years. It has been prepared under the Action for Butterflies project
which is funded by WWF-UK, English Nature, the Countryside Council for Wales and
Scottish Natural Heritage. The Action Plan was prepared in consultation with the following
organisations with the intention that they will participate in the actions outlined: English
Nature, Countryside Council for Wales, Ministry of Agriculture, Fisheries and Food, Welsh
Office Agriculture Department, Royal Society for the Protection of Birds, National Trust, the
Wildlife Trusts (Suffolk, Sussex, Hampshire, Dorset, Devon and Cornwall), the Forestry
Authority and the Forestry Commission (New Forest).
Outline Paper (first draft): ....................................................................................... January 1996
Pathfinder Meeting: ..................................................................................................March 1996
Second Draft: ............................................................................................................March 1996
Final Draft: ...................................................................................................................June 1996
Acknowledgements
We are grateful to the following for their comments at the Pathfinder meeting and / or on
subsequent drafts; Andrew Nicholson, Rees Cox, Stuart Graham, Richard Cottle, Neil Hill
(English Nature), Adrian Fowles (Countryside Council for Wales), Mike Clarke and Jon
Gulliver (Forestry Commission, New Forest), Peter Goatham and Brian Pickess (Royal
Society for the Protection of Birds), Nigel Bourn, Paul Kirkland and Peter Thornett (Butterfly
Conservation), Robin Crane (The Wildlife Trusts), Jenny Joy, Chris Thomas (University of
Leeds), Ken Wilmott, Simon Curson (Sussex Wildlife Trust), Clive Chatters (Hampshire
Wildlife Trust), Liesje Birchenough (Dorset Wildlife Trust), Nigel Webb (Institute of
Terrestrial Ecology), Ms A.E.Tarran (Ministry of Agriculture, Fisheries and Food) and Mr
M.D.Giles (Welsh Office Agriculture Department).
Butterfly Conservation Society (the British Butterfly Conservation Society) has an
overriding objective to ensure a future for butterflies, moths and their habitats. In order to
achieve this objective its aims are
 to raise public awareness of the plight of our butterflies and moths.
 to reduce the decline of commoner species and to increase the numbers of rarer species.
 to work with and advise other conservation groups, local bodies and agencies on techniques
of land management which favour butterflies and moths and related wildlife.
 to acquire and manage habitats for butterflies and moths.
 to encourage the research (both at amateur and professional levels) on butterflies and moths.
 support and encourage butterfly and moth conservation world-wide.
Registered Office of Butterfly Conservation: Shakespeare House, High Street, Dedham, Colchester, Essex, CO7 6DE.
Registered in England No. 2206468 Registered Charity No. 254937.
2
CONTENTS
Page
Summary
4
Part 1
1.1
1.2
1.3
1.4
Overview
Priority Statement
Broad Objectives
Legal Status
Status and Level of Biological Knowledge
Part 2
2.1
2.2
2.3
2.4
2.5
Biological Assessment
Introduction
Ecology
Distribution and Population
Limiting Factors
Resume of Conservation to Date
Part 3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
Actions and Work Programme
Policy and Legislative
Site Safeguard and Acquisition
Land Management
Species Protection and Licensing
Advisory
International
Future Research, Survey and Monitoring
Communications and Publicity
Review
Abbreviations
5
5
6
7
7
10
12
13
References
Appendix 1
Appendix 2
5
15
15
15
16
16
16
17
17
18
19
Distribution in the UK
Heathland management for the Silver-studded Blue
3
22
23
Summary

The Silver-studded Blue Plebejus argus is a nationally scarce species that is included in
the Guidelines for the Selection of Biological Sites of Special Scientific Interest (NCC
1989) and protected under Schedule 5 of the Wildlife and Countryside Act 1981 with
respect to trade. Although it has declined substantially through much of its range, it is
still locally abundant in heathlands in parts of southern England. A medium priority is
afforded to the conservation action in this plan to protect and increase the number of
Silver-studded Blue colonies in the UK.

The British population has four subspecies: P. a. argus is the lowland heathland form
found throughout its current range; P. a. caernensis occurs on calcicolous grassland in
North Wales; P. a. cretaceus is now confined to calcicolous grassland in Dorset; and P. a.
masseyi is a form found at a single moss site in Wales being extinct from Cumbria and
Scotland. The genetic distinctiveness of these races is currently under investigation.

The Silver-studded Blue has undergone a severe decline in range this century, estimated at
80%. It has become extinct in Scotland and northern England and throughout most of
central, eastern and south-eastern England. It remains widespread only on the heaths of
Dorset and Hampshire. It is regarded as an indicator of active lowland heathland
management.

The major threats to this species are heathland destruction, neglect or mis-management,
combined with the fragmentation of its habitat which increases local extinction and
prevents recolonisation. It requires foodplants growing alongside patches of open soil or
in short turf and strong populations of one of two species of ants with which it has a
relationship in its larval and pupal stages. These conditions are satisfied by habitats in
early successional stages or those maintained by grazing.

The major objectives of this plan are to ensure that existing populations are maintained
through appropriate habitat management and to encourage restoration of habitat
throughout its former range.

The objectives of this plan will be achieved by encouraging beneficial land management
on existing sites, especially those that occur on nature reserves; restoring and maintaining
a network of habitat between existing sites and within its former range; and conducting
strategic re-introductions. Further research and survey will be supported, particularly into
the status and ecology of the species in relatively little described parts of its range.

The Action Plan and the conservation of this butterfly will be publicised. Funds will be
sought to ensure that proposed actions are implemented.

The Action Plan covers the next ten years, will be monitored annually and reviewed in the
year 2000 or such earlier time as the situation demands.
4
Part 1
Overview
1.1 PRIORITY STATEMENT
The Silver-studded Blue is a nationally scarce species that is included in the Guidelines for
the Selection of Biological Sites of Special Scientific Interest (NCC 1989). It is a butterfly of
open ground supporting leguminous and ericaceous shrubs, and in Britain is primarily a
heathland species (although it inhabits calcicolous grassland in small parts of its range). It
has declined on heathland throughout Britain, becoming extinct in Scotland, absent in
northern, central and south-east England and severely reduced in abundance elsewhere. Its
main centres are the heaths of southern and south-west England, coastal Wales and parts of
East Anglia. Remaining heathlands are highly fragmented and often too small to support
colonies indefinitely as the species requires early successional, but transient habitats.
Although the species has declined substantially in the last fifty years, it is still locally
abundant in parts of its southern range. A medium priority should thus be afforded to
implementing this National Plan, but a high priority may be given in those regions which
have suffered a high rate of decline, or where it is reduced to a small number of populations.
1.2 BROAD OBJECTIVES
1. Maintain present range through suitable habitat management at a local and landscape
scale.
2. Encourage restoration of suitable habitats in present and former range, concentrating on
strategic sites and networks of habitats that will allow population spread and the maintenance
of metapopulations.
1.3 LEGAL STATUS
The Silver-studded Blue is listed on Schedule 5 of the 1981 Wildlife and Countryside Act for
sale only.
5
1.4 Status and Level of Biological Knowledge
Population
Knowledge of
-size
Confined to southern parts of
England, coastal Wales and parts of
East Anglia. Most remaining
colonies are small and isolated.
About 50 colonies in N. Wales, 31 in
Devon, 14 in Surrey, 10 in Suffolk
and one in Shropshire, although
most are small. Less detail for Dorset
and Hampshire where it is more
common, and Sussex, Norfolk and
Cornwall. Few extensive tracts of
habitat remain.
-trend, numbers
Recorded decline is severe, based on
knowledge of 10km squares.
Decline in numbers is continuing in
some areas. Smaller populations are
most vulnerable to extinction.
-trend, range
Severe contraction in range this
century (65%). Now extinct
throughout Scotland, northern
England and most of central, eastern
and south-eastern England.
-status
Good in most areas.
-trends
Good.
-conservation
requirements
Good. Responds well to correct
management.
6
Part 2 Biological Assessment
2.1 INTRODUCTION
The Silver-studded Blue Plebejus argus has undergone a severe contraction in range
throughout Britain and reductions in abundance in its remaining distribution (Heath et al
1984, Thomas 1993). It occurs in a variety of habitats: lowland acid heathland (dry and wet),
calcicolous grassland, sand dunes and lowland mosses (Emmet & Heath 1990). Heathland is
the most commonly used habitat in Britain and supports most of the population; colonies on
this habitat are the nominate subspecies P. argus argus. Populations on calcicolous
grasslands are now restricted to two locations: Great Orme's Head in North Wales (where P.
argus caernensis occurs) and the Isle of Portland in Dorset (P. argus cretaceus). Colonies on
the limestone of the Dulas valley in North Wales resulted from introductions made 50 years
ago (Marchant 1956). One mossland population remains (in North Wales) although the
species was once widespread in this habitat, especially in Cumbria (P. argus masseyi).
Extinct populations in Scotland are thought to have resembled P. a. masseyi (Thomson 1980).
The classification of these subspecies is based primarily on the size and colouration of adults
(Emmet & Heath 1990), but their status is uncertain (Dennis 1977, Thomas 1985a). The
genetics of isolated populations and subspecies are currently being studied.
2.2 ECOLOGY
The Silver-studded Blue occurs at high densities in closed colonies (Thomas 1985b,
Ravenscroft 1990a, Emmet & Heath 1990, Lewis et al. 1995). The butterfly is univoltine in
Britain, flying from July to August in most years, although in some years it may emerge in
mid-June (Heath, Pollard & Thomas 1984). Calcicolous populations usually emerge in June
in N. Wales (Thomas 1985a). In parts of central and southern Europe it is bivoltine,
emerging as early as May (Higgins & Riley 1970). The flight period lasts 4-5 weeks and
numbers reach pronounced peaks within 2-3 weeks of emergence at most sites studied. The
species exhibits protrandry, with males emerging before females.
Both sexes are highly sedentary and most individuals move less than 50m over their lifespan
(Thomas 1985b, Ravenscroft 1990a, Lewis et al. 1995). Adults take nectar from a variety of
plants depending on their availability (Bell Heather Erica cinerea, Cross-leaved Heath Erica
tetralix, Bramble Rubus fruticosus agg. and Bird's-foot Trefoil Lotus corniculatus) but are
limited to the flowers of heathers at most heathland sites (Ravenscroft 1990a, Joy 1992,
Wilmott 1994). Females feed more than males. Adults may congregate in conspicuous
roosts, often on heather bushes or grass tussocks, where they roost head downwards
overnight.
Females lay eggs singly close to the ground on a variety of plants, but usually on the woody
stems of heathers (Ling Calluna vulgaris, Bell Heather and Cross-leaved Heath) or Gorses
(Ulex spp.)on heathlands (Thomas 1985a, Ravenscroft 1990a, Joy 1992, Wilmott 1994) and,
especially in calcicolous habitats, on moss, lichens, twigs and leaf litter beneath prospective
foodplants (Thomas 1985a). The egg is the overwintering stage. They are usually laid
around the edges of short vegetation bordering patches of bare ground (Thomas 1985a). Eggs
are usually laid <7cm above the ground on heathlands in N. Wales (Thomas 1985a), <7cm
above the ground on heathland in Shropshire (Joy 1992), <10cm above the ground on
7
heathland in Suffolk (Ravenscroft 1986) and <3cm above the ground on calcicolous grassland
in N. Wales (Thomas 1985a). Exceptions have been noted at some sites, and females may
sometimes lay eggs high on grasses or in clusters under the fronds of sparse Bracken
Pteridium aquilinum at heights in excess of 30cm (Ravenscroft 1986, Mendel & Parsons
1987). No detailed work has been done in the Dorset and Hampshire strongholds but the egg
laying requirements are considered to be slightly less exacting in these southern locations.
Larvae hatch in Spring and are able to feed on a wide range of plants from three families (the
Leguminosae, Ericaceae and Cistaceae) (Thomas 1993). On heathland and moss sites the
important foodplants appear to be Bell Heather, Cross-leaved Heath, Gorse, Ling, and
probably Bird's-foot Trefoil where this occurs on grassy sites (heathland larvae prefer this last
plant in captivity, Thomas 1985a) (Thomas 1985a,b, Joy 1992, Wilmott 1994). On
calcicolous grassland, Bird's-foot Trefoil, Rock Rose (Helianthemum nummularium) and
Hoary Rock-rose (H. canum) are used in North Wales (and very rarely Thyme, Thymus
drucei) (Thomas 1985a) and Bird’s-foot Trefoil, Rock-rose and Horseshoe Vetch
(Hippocrepis comosa) in Dorset (Warren 1986, Wilmott 1994). On Continental Europe, a
wider range of plants may be used, including Bilberry (Vaccinium myrtillus), Broom (Cytisus
scoparius) (also used in the U.K., e.g. at Prees Heath, C.D. Thomas pers. comm.) and
Halimium halimifolium (Higgins & Riley 1970, Jordano et al 1992). In all parts of the range,
larvae feed primarily on the buds, flowers, growing tips or young leaves of plants. In the UK,
larvae are fully developed (about 13mm in length) by June.
Throughout development, the Silver-studded Blue has a highly developed relationship with
ants which is maintained by the production of sugar-rich liquid by the larvae and pupa.
Females respond to the presence of ants when selecting sites to lay eggs (Jordano et al 1992).
This may explain the tendency of females to lay on Bracken at some sites as this plant has
extra-floral nectaries attended by ants (Mendel & Parsons 1987). Larvae have a pair of
prominent reversible tentacular organs on the abdomen which attract and excite ants (perhaps
by emitting chemicals) and small glands (pore cupola organs) scattered over the body, some
of which may secrete sugar. They also have a nectary organ (Newcomer's organ) on the
abdomen which develops in the third instar and secretes sugar and amino acids (Malicky
1969, Fiedler 1989). Ants gather droplets secreted from the pre-cupola and Newcomer's
organs. Larvae are also covered with droplets when they hatch, pupae exude droplets and
adults emerge covered in droplets (Thomas 1985a, Ravenscroft 1990a, Jordano & Thomas
1992).
Ants tend larvae from hatching and through pupation. Full-grown larvae can be found in the
field resting on top of ant nests, in ant nests or under stones used by ants (Thomas 1985b,
Ravenscroft 1990a, Jordano et al 1992). On calcicolous sites in Dorset, larvae are thought to
spend most of their time in ant nests and emerge to feed by night (Wilmott 1994). The
ecology of the early instars is less clear. In captivity, ants are attracted to hatching larvae,
which may be carried off after emerging (Ravenscroft 1990a, Jordano & Thomas 1992) and
first and second instar have been found in ant chambers in the field (Wilmott 1994). It seems
likely that most larvae are taken into ant nests where they rest, emerging only to feed. Others
are tended where they occur on foodplants (Jordano et al 1992). Pupae are tended by ants
under stones, under mats of prostrate vegetation such as rabbit-cropped gorse, small holes in
the ground, in earthen cells constructed by ants or in ant nests (Thomas 1993, Jordano et al
1992, Emmet & Heath 1990). Although pre-pupal larvae are not thought to seek out ants
8
(Jordano et al 1992), a small nest may be established around the pupa (Emmet & Heath
1990). Adults emerge covered in ants which remain to gather droplets from their surfaces.
The benefit of this relationship to the Silver-studded Blue is probably protection from
parasites and predators, as has been demonstrated with closely related lycaenids (Pierce et al.
1987). Ants gain sugar and nutrition in return and there is evidence that ants which attend
such larvae have higher survival rates (Fiedler & Saam 1995).
The ants associated with the Silver-studded Blue are the common black ants Lasius niger and
L. alienus and the relationship appears to be Lasius-specific, although ants of other genera
will tend later instars in captivity (Jordano & Thomas 1992). In N. Wales, L. alienus is the
main ant on limestone and L. niger on heathlands (Thomas 1985a). On Suffolk heathlands,
the species used is site specific; L. niger is used at most sites but L. alienus takes over where
L. niger is absent on the driest heaths (Ravenscroft 1986). Lasius flavus (the Yellow Meadow
Ant) responds to larvae in captivity (Ravenscroft 1990a, Jordano & Thomas 1992) and is
abundant on some sites (Ravenscroft 1986), but has not been recorded with larvae in the field.
Habitat requirements
The Silver-studded Blue requires the presence of Lasius sp. ants, open ground for breeding
and either bare soil or short vegetation in all habitats in Britain. Choice of habitat varies from
region to region and this may reflect differences in ant densities. Colonies in southern
England may survive in places where heathers have become leggy, exposing bare ground
beneath (Thomas & Webb 1984). On heathlands and calcicolous grassland, adult densities
are correlated positively with a variety of indicators of the early stages of heathland and
negatively with vegetation height, although the overall relationship appears to be with ant
density (Jordano et al 1992, Thomas 1985b, Ravenscroft 1990a). The preferred conditions
produce warmer microclimates at ground level for larvae; a factor that is especially important
towards the north of the species' range (Thomas 1993). (At the southern limit in Spain taller
vegetation is preferred which reduces ground temperatures, Jordano et al 1992).
A warm microclimate is probably even more important to maintain the nest-building and
foraging activities of Lasius ants. Densities of adults are closely correlated with those of ant
nests (Ravenscroft 1990a) as is the distribution of eggs, larvae and pupae (Jordano et al
(1992). The highest densities of butterflies and ants in Suffolk occur where Bell Heather is
most abundant (6-30% ground cover) or where it replaces Ling altogether (Ravenscroft 1986).
Butterflies do not occur where ant nest density falls below 30 nests/ha and ants are largely
absent (<10 nests/ha) from dense or mature Ling dominated heathlands (>80% cover)
(Ravenscroft 1986, 1992a). In West Sussex, the butterfly occurs almost exclusively where
Bell Heather is abundant (Crane 1995). In Surrey, the butterfly is found in the presence of
Erica heather and 5-15% bare ground (Wilmott 1994). Bell heather therefore appears to
represent a good indicator of suitable conditions in many areas. In Dorset, however, the
Silver-studded Blue is most often associated with humid and wet heath where Cross-leaved
Heath is dominant and Bell Heather absent, but homogenous stands of Ling remain
unsuitable. On calcicolous grassland in N. Wales, the Silver-studded Blue is absent from sites
where ants are also largely absent (Jordano et al 1992).
Early successional stages, and those held in check by grazing (nowadays mainly by rabbits in
most areas, although the New Forest is pony/cattle grazed), are preferred in all habitats. On
9
heathland, there is a range of suitable conditions, from nutrient-deficient sandy soils to peaty
soils. Most heathland colonies exist on sites that have been either recently disturbed, such as
sand-pits, quarries and firebreaks, or burnt (Thomas 1985b, Ravenscroft 1990a, Wilmott
1994). Conditions usually become suitable after 2-5 years of re-growth. In the absence of
traditional management, such as cutting of heathers and invasive scrub, grazing of domestic
animals, or burning to encourage young growth for livestock, suitable conditions on
heathlands are short-lived, perhaps 5-10 years (Thomas 1985b). Exceptions occur where
heathland is grazed by rabbits, which maintain open, short vegetation; in wet hollows on
humid heaths where vegetation succession is slowed by the prevailing conditions; and also in
extreme southern counties like Dorset and Hampshire where slightly taller vegetation may be
tolerated. On calcicolous grassland, conditions persist for much longer, and on Great Orme's
Head continuous sheep and goat grazing may maintain suitable conditions indefinitely,
although the butterfly may be excluded from areas that are too heavily grazed (Thomas
1985b). Ideal conditions are found in 2-7cm tall vegetation and with some broken turf
(Thomas 1985b). The requirements and ecology of the butterfly in sand dune systems, which
are used in some parts of the range are less well-studied. Here, they occupy mobile or grazed
dunes and probably feed on Bird's-foot Trefoil, although the foodplant is not always clear (M.
Oates pers. comm.).
A summary of requirements is given in Appendix 2.
2.3 DISTRIBUTION AND POPULATION
Distribution
The Silver-studded Blue occurs across the temperate areas of Europe and Asia to Japan
(Higgins & Riley 1970). In continental Europe, it occurs in a wider range of situations than
in the British Isles, including alpine grassland, meadows, forest clearings and xerophytic
shrubland. It occurs in most parts of Europe except northern Scandinavia (Higgins & Riley
1970). In Britain it was widely distributed at the turn of the century but it has since
undergone a substantial decline and has become extinct except in southern and south-western
England, and small parts of East Anglia, coastal Wales and the West Midlands (Heath et al.
1984, see Appendix 1). It is now common only in Dorset and Hampshire. The butterfly also
occurs on the Scillies and Channel Islands. It used to occur in Scotland around the turn of the
century (Heath et al 1984), although there is doubt over some of the records (Thomson 1980)
(the only known specimen is from Loch Rannoch in 1936). It was once quite common in
Cumbria and Lancashire (Birkett 1957) before its extinction in about 1942 (Thomas 1985b).
Extinctions elsewhere in northern and central England and Wales occurred largely before
1940 (Thomas 1985b). 44% of pre-1940 10km squares were lost between 1945 and 1970 and
65% up to 1982 (Thomas 1985b, Warren et al. in prep).
Population size
The species tends to occur in high densities on small patches of suitable habitat. However,
colonies can be short-lived, becoming extinct rapidly if habitat deteriorates. A survey in
North Wales identified about 47 colonies, over 20% of which are large (>4000 adults at the
peak of the flight period) (Thomas 1985b). Ten of these are on Great Orme's Head where
10
some 250,000 adults occur at the peak of the flight period; these populations appearing stable
from 1983-1990 (Thomas 1993). Most patches occupied on limestone are between 0.1 and 8
ha and just one site is larger than 8 ha (Thomas 1985b). Heathland populations in North
Wales (20) are smaller; the largest is at South Stack, Anglesey (c. 40,000 adults at peak); but
most are 40-4000. 72% of heathland colonies occupy 0.1-1.45 ha and just one site is larger
than 8 ha (Thomas 1985b). These also appeared stable in the period 1983-1990 (Thomas
1993). Sixteen colonies which have resulted from an introduction to the limestone of the
Dulas valley are similar in size to the heathland population. The sole mossland colony has
remained at 5000 adults on 4 ha (Thomas 1985b, 1993).
In Suffolk, there are now just eleven colonies in three isolated regions. The species used to
be abundant here and on the Brecklands further west (Mendel & Piotrowski 1985). Only one
colony is substantial (c. 7000 adults at 1986 peak on 11 ha) and here numbers and the area
occupied continues to decline (2000 on 6 ha in 1994) (Ravenscroft 1990a,b, 1994). All other
colonies are small (<2000 adults on <2 ha) and less than 1% (19 ha) of available heathland
was occupied in 1986 (13.5 ha in 1994). One small colony was founded between 1985-1994
and one became extinct. Two other colonies were established by introductions in 1986
(Ravenscroft 1992a,b).
In Shropshire, one colony survives on 8 ha of Prees Heath (125 ha) (c 4000 adults at peak;
Joy 1992). In Dorset, it is abundant on heathland (Thomas & Webb 1984), the subspecies
cretaceus occupied 159 ha of limestone grassland in disused quarries on the Isle of Portland
in 1985 (Warren 1986). The status of this unique subspecies is cause for concern: recent
surveys suggest that many colonies are small and several have been lost in the last 15 years,
primarily through increased quarrying (P. Green, pers. comm., A. Nicholson pers. comm.). In
Devon, the butterfly occurs in 31 colonies on the East Devon Commons, but most colonies
appear small and the majority of heathland is unoccupied (Thornett 1995). West Surrey
supports 14 colonies of unknown size (Wilmott 1994). There is less detail available on the
status of the Silver-studded Blue elsewhere in its range, such as in the New Forest, Cornwall,
South Wales and Norfolk.
Population structure
The population structure of the Silver-studded Blue is one of the best studied of British
butterflies. The species exists in metapopulations* and their function has been well defined in
heathland populations in N. Wales (Thomas & Harrison 1992, Thomas 1996). Because
suitable conditions on heathland are short-lived, it cannot persist on heathland that is:
(1) not managed; or
(2) too small to provide a continuation of conditions through natural events; or
(3) too isolated to allow recolonisation should a population become extinct.
The persistence of the Silver-studded Blue therefore depends on suitable habitat being
continuously available within either relatively large areas of habitat or as a closely linked
network of smaller sites. Within heathland metapopulations, local extinctions are usually
*
a metapopulation is a collection of local populations, connected by occasional dispersal, in
which there are local extinctions and colonisations (Gilpin & Hanski 1991).
11
confined to small colonies of <0.9 ha (Thomas & Harrison 1992). On limestone habitats,
extinctions and recolonisations most often occur on smaller patches (<0.2 ha) because
conditions in these habitats usually persist for longer (Thomas & Harrison 1992).
The recorded mobility of the Silver-studded Blue is low. In N. Wales, 89% of movements by
adults within a day are <20 m, and none were recorded >50 m (Thomas 1985a). Isolated
individuals sometimes move up to 400 m from a colony, but migration over 1km is thought to
be very rare. Only about 1.4% of marked adults moved between habitat patches separated by
13-200 m in N. Wales (Lewis et al. 1995). No colonisation has been noted over 600 m in N.
Wales, although all suitable patches of habitat within 1km existing populations tend to be
occupied (Thomas & Harrison 1992). In Suffolk, 74% of adult movements were below 20 m,
7% >50 m and small pockets of adults occur within 500-600 m of colonies (Ravenscroft
1990a). However, larger scale movement does occasionally occur, an exchange of
individuals having been noted between two colonies separated by 1.5 km and a colony was
apparently founded over 3.5km in 1994 (Ravenscroft 1994).
2.4 LIMITING FACTORS
Historical
Habitat loss, through:
(1) Destruction, mainly by agriculture, forestry, industry (including mineral extraction) and
housing;
(2) Decline of traditional management (turf and scrub cutting, burning and domestic
grazing) leading to loss of early successional conditions and succession to scrub;
(3) Decline in rabbit populations owing to myxomatosis, although recent rabbit
recovery has reversed this in some areas.
Ensuing effects on colonisation potential:
(1) isolation of sites, preventing colonisation of suitable habitat;
(2) reduction in rate of habitat creation owing to decline in traditional management;
(3) reduction of site size, reducing likelihood of creation of suitable conditions
sites
through natural events in the absence of management.
Current and potential
Continuing destruction of heathland.
Absence of suitable management.
12
within
Inappropriate heathland management.
Any decrease in rabbit populations through disease causing a reduction in grazing pressure
(although many calcicolous grasslands are overgrazed).
Associated effects of site isolation and heathland fragmentation as described above.
Increased quarrying activities on the Isle of Portland.
2.5 RESUME OF CONSERVATION TO DATE
The Silver-studded Blue has been well studied in many parts of its range, especially where the
species is rare. It is regarded as a characteristic species of lowland heathland and an indicator
of active lowland heathland management. Studies have been performed in North Wales
(Thomas 1983, 1985a,b), East Anglia (Ravenscroft 1990a,b, 1994), Shropshire (Thomas
1985a,b, Joy 1992), Surrey (Wilmott 1994), Devon (Read 1985, Thornett 1995), Dorset
(Webb & Thomas 1994), Sussex (Crane 1995) and parts of Dorset (Warren 1986), although
not all of these describe status. There has been comparatively little study of status where the
species is more common on the heaths of southern England e.g. in Hampshire and Cornwall.
The Silver-studded Blue is well-represented on nature reserves, SSSIs and other protected
areas owing to the high degree of protection afforded to heathland. In N. Wales, 17 of 47
colonies are on nature reserves (mainly LNRs on Great Orme's Head which is a Country Park,
six on RSPB reserves, two on NNRs) and the remainder are privately owned (Thomas
1985b). In Suffolk, small populations occur on two NNRs, three on an RSPB reserve, one on
NT land and most of the remaining sites are on SSSIs and Council owned (Ravenscroft
1994). In Surrey, parts of three colonies occur on NT ground and two on reserves of the
Surrey Wildlife Trust. Only two sites are privately owned, the remainder are owned by
various local Government authorities (Wilmott 1994).
Elsewhere, large areas of heathland supporting the Silver-studded Blue are owned or
managed by conservation organisations (e.g. in Dorset there are six NNRs and three RSPB
reserves with the species and many smaller nature reserves of the Dorset Wildlife Trust and
Local Authorities, A. Nicholson pers. comm.). On the Isle of Portland most colonies of the
cretaceus race are within an SSSI and one colony occurs on a Butterfly Conservation reserve.
The butterfly occurs on at least two Sussex Wildlife Trust reserves. In Hampshire, the
Silver-studded Blue is ubiquitous in the New Forest, most of which is SSSI and managed by
the Forestry Commission. Elsewhere in the county, Hampshire Wildlife Trust have at least
three reserves supporting the butterfly. The RSPB manage Aylesbeare in Devon and Grange
Heaths in Dorset, and in Cornwall there are large areas of NT ground e.g. at Holywell Dunes
and on the Lizard, and at least two Cornwall Wildlife Trust Reserves with the species. In
South Wales, the Silver-studded Blue occurs on at least one area of NT land in
Pembrokeshire.
In some parts of the range of the Silver-studded Blue there are specific heathland projects.
These include:- the Heathlands Project Team of the RSPB in Dorset; English Nature's
Wildlife Enhancement Scheme also in Dorset as well as Hampshire; the Suffolk Coast and
13
Heaths Project (Suffolk County Council); The Sandlings Project (Suffolk Wildlife Trust); the
NE Hampshire Heathlands Project (mainly Local Authorities); the Surrey Heathland Project
(mainly Local Authorities); and in Sussex, the Heathlands Project of the South Downs
Conservation Board. Cornwall Wildlife Trust have a heathland conservation project in
conjunction with the RSPB (NB. this is not an exhaustive list).
The distribution and sizes of populations occurring in some parts of the range are well
monitored (North Wales; Thomas 1983, 1985a,b, 1993, Thomas & Harrison 1992: Suffolk;
Ravenscroft 1986, 1987, 1990b, 1994). Many other colonies are monitored by site managers,
especially on nature reserves. These include wardens of the RSPB at Minsmere (Suffolk),
Aylsebeare (Devon), Arne (Dorset) and South Stack (N.Wales) and English Nature at
Studland, Hartland Moor and Stoborough Heath (Dorset). Branches of Butterfly
Conservation (particularly Hampshire, Devon, Sussex, Surrey, Suffolk and Dorset) are active
in monitoring populations and managing further sites.
A full review of the status of the Silver-studded Blue on conservation sites (and their
management priorities) and monitoring activities throughout England and Wales is required.
Introductions
A number of introductions and re-introductions of the Silver-studded Blue have been
attempted by conservationists and justified because:
(1) its habitat is now so fragmented;
(2) the species has limited colonisation potential;
(3) many suitable, unoccupied patches of habitat exist;
(4) the suitability of these patches is relatively easy to assess.
Re-introductions represent an attempt to restore dispersal in modern fragmented landscapes
(Thomas 1993). Well-documented introductions of the Silver-studded Blue have been made
in N. Wales and Suffolk and demonstrate the potential with this species. In the former, 90
adults were released in 1942 in the Dulas valley, near Great Orme's Head (Marchant 1956).
There are now an estimated 16 colonies and 30,000 adults (at peak) spread along the
limestone valley (Thomas 1985b, 1993). Six other introductions were made elsewhere in N.
Wales 1978-1983: two are still extant (one heath, one calcicolous); two survived for 2-7 years
(both heathland); and two failed (one calcicolous, one heathland) (Thomas & Harrison 1992).
In Suffolk, introductions were made at two sites in 1986 using stock from a site due for
development (Ravenscroft 1987). Both were extant in 1994 and one has become the largest
colony in Suffolk and spread to nearby heathland (Ravenscroft 1992a,b, 1994). In 1994,
stock from Prees Heath in Shropshire were released on the Wirral where the species used to
occur (J. Joy pers. comm.).
Management
Management for the butterfly has been summarised recently by Joy (1995). Regional
accounts and specific recommendations can be found in Thomas (1983, 1985b), Read (1985),
14
Ravenscroft (1990a,b, 1994), Crane (1995), Joy (1992) and Wilmott (1994). A summary of
the main points is given in Appendix 2.
Part 3
Actions and Work Programme
This section has been divided into the standard headings Policy and Legislative; Site
Safeguard and Acquisition; Land Management; Species Protection and Licensing; Advisory;
International; Future Research and Monitoring; Communications and Publicity; Review.
Actions appear under one heading according to their major role and/or aim, and are given a
low, medium or high priority. The lead organisation(s) concerned for each action is/are
named.
Lead
organisations
concerned
3.1 POLICY AND LEGISLATIVE
Action 1
PRIORITY: HIGH
Include habitat requirements of the Silver-studded Blue where
appropriate in management prescriptions for ESAs, Countryside
Stewardship, Habitat Scheme and other schemes (Wildlife Enhancement
Scheme etc.)
MAFF,
WOAD, EN,
FA, CCW
3.2 SITE SAFEGUARD AND ACQUISITION
Action 2
PRIORITY: HIGH
Protect strategic metapopulations through management agreements
and/or reserve acquisition.
Action 3
PRIORITY: MEDIUM
Ensure development proposals do not adversely affect existing or
potential habitats.
3.3
ALL
LAND MANAGEMENT
15
ALL
Action 4
PRIORITY: VERY HIGH
Promote beneficial heathland management in areas where the Silverstudded Blue exists, and restore links between populations.
Action 5
PRIORITY: HIGH
Promote beneficial grassland management for the calcicolous populations
of Great Orme's Head and the Isle of Portland.
Action 6
BC, WTs,
FC(New
Forest), FE,
NT, EN,
CCW, RSPB,
LAs
BC, LAs, EN,
CCW.
PRIORITY: MEDIUM
Restore suitable habitats in former range, initially concentrating on areas
close to existing populations (south-east, south-west, eastern and midland
England, see Appendix 1).
ALL
3.4 SPECIES MANAGEMENT, PROTECTION AND LICENSING
Action 7
PRIORITY: LOW
Conduct strategic re-introductions to suitable networks of habitats within
former range using appropriate stock.
Action 8
BC, EN,
CCW, WTs,
NT, RSPB.
PRIORITY: HIGH
Prepare separate action plans for high priority regions (North Wales,
South Wales, Suffolk, Norfolk, Cornwall), following targets of UK
Biodiversity Action Plan (within three years).
BC, EN,
CCW
3.5 ADVISORY
Action 9
PRIORITY: HIGH
Advise conservation agencies, site owners/managers and project officers
of the relevant agri-environmental schemes and their role in promoting
suitable habitat management for the Silver-studded Blue.
3.6
INTERNATIONAL
No actions proposed
16
BC, EN,
CCW, MAFF,
WOAD
3.7
FUTURE, RESEARCH, SURVEY AND MONITORING
Action 10
PRIORITY: HIGH
Survey status of Silver-studded Blue in less well-documented parts of its
range (South Wales, Norfolk, Cornwall and parts of Hampshire).
Action 11
PRIORITY: HIGH
Review the status of the Silver-studded Blue throughout its range,
especially on sites of conservation activity and current or planned
management.
Action 12
BC, CCW,
EN
PRIORITY: HIGH
Investigate ant habitat preferences on heathland and those of the Silverstudded Blue on southern heathland and sand dunes and the implications
for habitat management.
3.8
EN, CCW,
BC
PRIORITY: MEDIUM
Collate transect and management data from all monitored sites (in
addition to BMS) annually and calculate annual index to compare trends
on individual sites. Review and extend work if necessary.
Action 14
BC, EN,
CCW
PRIORITY: MEDIUM
Survey suitability of potential networks of sites throughout former range
of the Silver-studded Blue and identify strategic sites for restoration
and/or introductions.
Action 13
BC, NT, WTs,
CCW, EN
BC, EN,
CCW, ITE,
Univs
COMMUNICATIONS AND PUBLICITY
Action 15
PRIORITY: HIGH
Publicise this Action Plan, the status of the Silver-studded Blue and the
measures being taken to conserve it.
17
BC, EN,
CCW
Action 16
PRIORITY: HIGH
Produce management guidelines for use by staff preparing management
plans for sites with colonies being entered into agri-environmental
schemes.
3.9
BC, EN,
CCW, MAFF,
WOAD
REVIEW
Action 17
PRIORITY: MEDIUM
Monitor this Action Plan annually and update every five years as
necessary.
BC, EN,
CCW
Key to abbreviations
BC
CCW
EN
ITE
FA
FC
FE
LAs
MAFF
NT
RSPB
Univs
WOAD
WTs
Butterfly Conservation
Countryside Council for Wales
English Nature
Institute of Terrestrial Ecology
Forestry Authority
Forestry Commission (New Forest)
Forest Enterprise
Local Authorities
Ministry of Agriculture, Fisheries and Food
National Trust
Royal Society for the Protection of Birds
Universities
Welsh Office Agriculture Department
The Wildlife Trusts
18
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19
Malicky, H. (1969). Verusch einer Analyse der ökologischen Beziehungen zwischen
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21
Appendix 1
Distribution of the Silver-studded Blue in the UK
(produced with kind permission of the Biological Records Centre).
22
Appendix 2
Heathland management for the Silver-studded Blue
Heathland management for the butterfly has been summarised recently by Joy (1995).
Regional accounts and specific recommendations can be found in Thomas (1983, 1985b),
Read (1985), Ravenscroft (1990a,b, 1994), Crane (1995), Joy (1992) and Wilmott (1994).
Grassland management for calcicolous populations is described in section 2.2 (see also
Thomas 1985b and Warren 1986).
Successful management aims to produce a mosaic of heathland of different stages and a
continual presence of early successional vegetation. This is less important on large expanses
of habitat where suitable conditions are likely to occur through random events such as
disturbance and burns, and, if resources are limiting, management should focus on small
heathland habitats, especially those linking larger populations. Suitable management
techniques will vary from region to region and should be determined locally in
association with management of the whole ecosystem. There are potential conflicts in
management priorities on heathlands; suitable conditions for some uncommon birds and
reptiles tend to be the later successional stages of heathland.
Burning/grazing
Periodic, patchy/small scale burning can be beneficial but needs to be considered carefully
because of the risks involved. Summer burning is illegal (although can occur with a special
MAFF/WOAD licence). However, accidental summer burns can be beneficial as they
remove more of the litter layer than winter burns and promote recolonisation of heathers of
open ground. All colonies in Suffolk show some evidence of previous burns and small
summer burns are readily colonised (Ravenscroft 1994). Some colonies in Surrey are on
accidental burns (Wilmott 1994). Large areas of sandy soils dominated by gorse would
become suitable if burned; even isolated cutting and burning in small piles would produce
patches of habitat. Conditions in most areas take 2-5 years to become suitable and remain
suitable for 10-15 years.
Moderate grazing by sheep and goats will maintain suitable conditions on calcicolous habitats
indefinitely (Thomas 1985b) and rabbit grazing and digging will prolong conditions on
heathland (Thomas 1985b, Ravenscroft 1990a, Joy 1995). The New Forest remains grazed.
The presence of large herbivores may also help maintain soil disturbance. Re-instating
grazing alone, however, is unlikely to be sufficient to restore conditions for the Silver-studded
Blue.
Soil disturbance and stripping
Disturbance of the ground, especially if the topsoil is removed, is the main progenitor of
suitable conditions in North Wales (Thomas 1985b). Most of the best sites here have had
their topsoil removed at some time. Elsewhere, colonies are found in abandoned quarries
(Dorset, calcicolous sites), old sandpits, disused sawmills (Suffolk), abandoned military
installations (Shropshire, Suffolk) and firebreaks across heaths (most areas). Rotavation of
sandy soils will re-create conditions, but may not suffice on more nutrient-rich soils (Thomas
1985b). Stripping topsoil may be a valuable tool in the restoration of former sites, after the
23
removal of any scrub and Bracken. Experimental strips removed on a colony being
overwhelmed by grasses in Suffolk in 1986 are now the main parts of the site occupied
(Ravenscroft 1994).
Cutting/mowing
Cutting and mowing can maintain areas for Silver-studded Blues in the absence of grazing, by
keeping vegetation short and exposing areas of open ground. Small numbers of the butterfly
frequent the edges of firebreaks on heathland that are regularly mown in many parts of the
range (Thomas 1985b, Ravenscroft 1990a, Joy 1995), but this is not thought to represent good
long-term management in Sussex (Crane 1995). However, in Dorset some large colonies
occur in and around regularly mown heathland. Forage harvesting of mature heather areas
can produce suitable habitat if debris is removed.
24