Silver-studded Blue

Plebejus argus (ple-BEE-uss AR-guss)

Silver-studded Blue male - Iping Common, Sussex 28-June-2013
Photo © Neil Hulme

26 - 32mm

Checklist Number

Family:LycaenidaeLeach, 1815
Subfamily:PolyommatinaeSwainson, 1827
Tribe:PolyommatiniSwainson, 1827
Genus:PlebejusKluk, 1780
Species:argus(Linnaeus, 1758)
Subspecies:argus (Linnaeus, 1758)
 cretaceus Tutt, 1909
 masseyi Tutt, 1909
 caernensis Thompson, [1937]

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The Silver-studded Blue gets its name from the light blue reflective scales found on the underside of most adults and which are quite visible when light reflects off them. As with many other species of blue, the males are blue while the female is a less-conspicuous brown. However, this butterfly is highly variable in appearance and, as stated in Dennis (1977), variation extends to "differences in the male upperside coloration, the width of the marginal border (wide in the New Forest, narrow in Devonshire) and the underside grey coloration (dull grey in the New Forest, silvery grey in east Suffolk); in the female to the development of the blue coloration and the orange lunules on the upperside, and on the underside to the coloration, the width and prominence of the medial white band".

Both Worms (1949) and Thomas (1999) provide an analysis of many populations found in the British Isles, all of which are considered to belong to the nominate subspecies by default, despite apparent differences in appearance. This includes populations found on mossland at Llyn Hafod-y-llyn in north Wales, on limestone at Portland Bill in Dorset, at Holy Island off Anglesey, at Prees Heath in Shropshire, and on the sand dunes of south-west England.

This delightful butterfly is found in close-knit colonies, with individuals rarely flying any distance. Most colonies contain less than a thousand adults. However, a few colonies are huge, with the number of adults measured in tens of thousands, providing an amazing spectacle. Most colonies of this species are found in southern England, although there are several other notable colonies in the east of England and Wales. With the exception of a single site at Prees Heath in Shropshire, this butterfly is absent from central and northern England, Scotland, Ireland and the Isle of Man.

Plebejus argus ssp. argus

This species was first defined in Linnaeus (1758) as shown here (type locality: Europe, Africa).

The British population is now represented by the nominate subspecies, with the exception of the population found on the Great Orme and nearby areas in north Wales, where it is replaced by the subspecies caernensis. Former populations of subspecies masseyi and cretaceus are now extinct.

Silver-studded Blue (male), Stedham Common (12 June 2012)

Photo © Mark Colvin

Silver-studded-Blue- 5D33389 Prees Heath July 2013

Male Underside
Photo © IainLeach

Silver-studded Blue female - Iping Common, Sussex 28-June-2013

Photo © Neil Hulme

Silver-studded-Blue- 5D31614

Female Underside
Photo © IainLeach

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Plebejus argus ssp. cretaceusHistoric Specimens

This subspecies was first defined in Tutt (1909a) as shown here (type locality: Dover, Kent, England).

This reference merely names the subspecies, but defers the description to Tutt (1909b), which itself refers back to Tutt (1909a) and also mentions Barrett (1893), Jones (1905a) and Jones (1905b). This subspecies is extinct and was formerly found on chalk downland in Kent, Surrey, Hampshire and Dorset. It differs from the subspecies argus as follows:

  • 1. It is slightly larger in size, on average.
  • 2. The male upperside is of a brighter blue.
  • 3. The male upperside has narrower dark borders.
  • 4. The male upperside hindwing has distinct marginal spots, rather than a dark band.

The colony found in the quarries of Portland Bill exhibits characteristics that are similar to this subspecies.

Plebejus argus ssp. cretaceus (Tutt, 1909)

var. cretaceus, Tutt, "Ent. Rec.," xxi., pp.58-59 (1909) [Tutt (1909a)]. Aegon, Barr., "Lep. Br. Isl.," pl.xi., fig.1 (1893) [Barrett (1893)]. Hypochiona, Jones, "Ent. Mo. Mag.," xli., p.254 (1905) [Jones (1905a)]; "Proc. Ent. Soc. Lond.," p.xlvi (1905) [Jones (1905b)].

♂. Bright blue, dark margin of forewings narrow or absent (sometimes quite pallid), discoidal lunules obsolete, on hindwings; interneural marginal spots replace usual band; underside bluish-grey, spots clearly defined.

♀. Dark fuscous, often tinged with blue, orange marginal lunules on hindwings poorly developed, on forewings usually obsolete; underside pale brownish, with well-defined spots, and whitish submarginal border.

This is the form that we noted (British Butterflies, p.183) [Tutt (1896a)] as "occurring near Dover and in other chalky districts, the ground colour of the males much paler in tint that those from the heathy localities, and the dark margin practically obsolete." It is the common form found on the open downs of southern England, and has a wide distribution on the Continent. It is most closely allied to aegiades, Gerh. (anteà p.192), but has well-developed metallic kernels on the underside of the hindwing, and is also very similar in its general characters to the specimens of var. orientalis in the British Museum coll. (anteà pp. 192-193).

ssp. cretaceus - Male Upperside [Richard Lewington]

Photo © Richard Lewington

ssp. cretaceus - Male Underside [Richard Lewington]

Male Underside
Photo © Richard Lewington


Female Underside

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Plebejus argus ssp. masseyiHistoric Specimens

This subspecies was first defined in Tutt (1909a) as shown here (type locality: Witherslack Mosses, Westmorland, England).

In the original definition of masseyi, the authors refer to Massey (1895), saying "The third form above [ssp. masseyi], the moorland form, was largely on our authority referred (Ent. Rec., vii., p.128) to the var. corsica, Bellier. This conclusion was based on a male and female received from Mr. W.E. Nicholson from Lewes, as var. corsica, the two forms agreeing fairly well on the upperside, especially in the female, but it is, we have since discovered, on the underside that Bellier de la Chavignerie found the chief character of the Corsican form, and, in this, our "moorland" form disagrees entirely. This form, like our "down" form, therefore, appears to required a distinctive cognomen, and we shall deal with it in our revision of the species as var. masseyi, as we are indebted entirely to Mr. Massey for our examples of the species, from which our studies have been made, and we owe him some apologies for misleading him, in our ignorance, into applying the name corsica, to our insect, on the first introduction of the race to the notice of British lepidopterists".

The corresponding description of masseyi, given below, is found in Tutt (1909b) and also refers to Massey (1895), Murray (1897) and Tutt (1909a). This subspecies was formerly found on the mosses of Westmorland and Lancashire, but has been extinct since approximately 1942. It differs from the subspecies argus as follows:

  • 1. The male upperside is often of a brighter blue.
  • 2. The male upperside has a reduced dark border, revealing dark nervures on the outside of the forewings, and a row of black spots on the hindwings.
  • 3. The male underside is paler, with reduced orange markings at the margins.
  • 4. The female upperside, which characterises this subspecies, has a blue flush that extends over most of the hindwings and the base of the forewings, leaving a broad brown outer margin.

The colony at Prees Heath exhibits some characteristics of this subspecies. Another site, at Hafod Garregog National Nature Reserve in north Wales, represents the last mossland site for Silver-studded Blue, and also resembles this subspecies to a degree, with some females exhibiting an amount of blue scaling.

Plebejus argus ssp. masseyi (Tutt, 1909)

var. masseyi, Tutt, "Ent. Rec.," xxi., p.58 (1909) [Tutt (1909a)]. Corsica, Massey, "Ent. Rec.," vii., pp. 127 et seq. (1895) [Massey (1895)]; Murray, "Ent. Rec.," ix., p.294 (1897) [Murray (1897)].

♂s varying in colour from those having a distinct argus (aegon) tint (with just a trace of red in it), to the blue which characterises argyrognomon. The dark marginal border is narrow, and, in some specimens, restricted to a fine line, with dark nervures showing on the outside of the wing. The hindwings in all the specimens present a more or less complete row of marginal black dots, separated by the fine black nervures, and, in some specimens, edged externally with paler - one specimen shows a pale coloration along the costa, and at the upper part of the outer margin of the hindwing. The undersides of the forewings of the ♂s may be described as pale grey with blue bases, with but little orange on the marginal border, and with slight variation in the size of the spots forming the transverse angulated row crossing the forewings. The hindwings are characterised by a white band between the marginal row of orange spots and the transverse row of black spots, the latter of which in the antepenultimate spot shows some tendency to vary, in some specimens being much higher than, in others more in a line with, the remainder.

The upperside of the ♀s is most remarkable, the forewings being blue at the base, the colour extending to the centre of the wing, and reappearing again as a transverse shade reaching from the costa to the inner margin, leaving the broad brown outer marginal band, which is so characteristic of the ♂ P. argus (aegon). Faint traces of orange spots are sometimes present in this outer marginal band. The hindwings are shaded entirely with blue, which is of two tints, as in the ♂s, the more purple argus (aegon) tint and the bluer argyrognomon tint, the latter very bright and characteristic; a series of marginal spots is present in all the specimens, but the quantity of orange present is distinctly limited. The undersides of the ♀s are characterised by the distinct white band which traverses all the wings between the orange marginal band and the transverse row of black spots, and also by the strong development of the silver studs in the orange bands. There is also some variation in the transverse band of spots on the hindwings, the antepenultimate spot being well raised out of the level of the others (an argus character) in some specimens, whilst it is almost in a line with the other spots (an argyrognamon character) in other specimens. In colour the undersides are pale grey with a brownish tinge, but with scarcely a trace of greenish-blue at the base (completely absent in some).

ssp. masseyi - Male Upperside [Richard Lewington]

Photo © Richard Lewington

Male Underside

ssp. masseyi - Female Upperside [Richard Lewington]

Photo © Richard Lewington

Female Underside

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Plebejus argus ssp. caernensis

This subspecies was first defined in Thompson (1937) (type locality: Great Ormes Head, North Wales).

This subspecies was formerly restricted to the Great Ormes Head in Caernarvonshire, North Wales. However, in 1942, 90 adults were introduced to the Dulas Valley, some 13km to the east, and the colony has gradually spread along the valley at a rate of 1km per decade, colonising 15 new sites. It is estimated that the total population now numbers 100,000. This subspecies differs from the subspecies argus as follows:

  • 1. It is smaller in size.
  • 2. The male upperside has narrower, sometimes absent, dark borders.
  • 3. The male underside is paler.
  • 4. The female upperside has a blue flush that extends over most of the hindwings and base of the forewings.

Plebejus argus ssp. caernensis (Thompson, 1937)

Male. Very much smaller than type argus, those in my series varying between 16 mm and 22 mm when fully expanded. In colour they are much paler than the type, approaching the shade of argiolus; the black border is greatly reduced, and in some specimens almost absent.

The underside varies from chinese white to a beautiful steely grey, but all the markings are smaller than usual and the lunules dull and inconspicuous.

Female. Smaller than the male, varying from 15 mm to 20 mm. The majority are very strongly suffused with purple blue, and the upperside variation is so great that I must divide them into four sections. I allot a varietal name to each.

var. splendida. Specimens entirely suffused with blue, the brown scaling being obliterated.

var. pseudomasseyi. Specimens suffused with blue on all parts except a circular patch on the discal area of the forewings. (Almost the same as Tutt's description of var. masseyi).

var. semisuffusa. The blue suffusion confined, or almost so, to the hindwings.

var. pulchrina. Forewings without blue markings but the hindwings brilliantly rayed with bright blue.

In each of the above varieties the blue suffusion may be any shade from a deep violet-purple to a brilliant greenish-blue, almost the tint of bellargus. On the upperside of the female the orange lunules are usually almost inconspicuous, and often entirely absent.

Caernensis occurs at a considerable elevation on limestone cliffs near the sea; and feeds, so far as I have been able to ascertain, exclusively on Rock Rose (Helianthemum). The time of its appearance is much earlier than type argus, at any rate in Wales, often emerging as early as the second week of June. This form never flies with the type, but is confined to totally different surroundings and conditions. There are many localities for type argus in the district, but all these are situate on sandy heaths and low lying waste lands; whenever a colony is found on the cliffs it is composed entirely of caernensis.

Silver-studded Blue - imago - Great Orme, North Wales - 25-Jun-13-37

Photo © Pete Eeles

Silver-studded Blue - imago - Great Orme, North Wales - 25-Jun-13-01

Male Underside
Photo © Pete Eeles

Silver-studded Blue - imago - Great Orme, North Wales - 25-Jun-13-27

Photo © Pete Eeles

Silver-studded Blue - imago - Great Orme, North Wales - 25-Jun-13-35

Female Underside
Photo © Pete Eeles

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Conservation Status

Although long-term declines in distribution seem to have stabilised, there are no signs that this decline is reversing. This species has suffered from increasingly-fragmented habitat as heathland is lost to development and agriculture. This species rarely flies any distance, often moving less than 20 metres in its life, making it difficult for this species to colonise new sites that may be close by. This species is therefore a priority species for conservation efforts.

UK BAP StatusDistribution Trend (%)Population Trend (%)
Priority Species
Click here to access the Biodiversity Action Plan (BAP) for this species.

The table above shows the distribution and population trends of species regularly found in the British Isles. The distribution trend represents a comparison between data for the periods 1995-1999 and 2005-2009. The information provided is taken from the Butterfly Conservation report The State of the UK's Butterflies 2011. The UK BAP status is taken from the UK Biodiversity Action Plan (UK BAP) (2007 review).


This species is typically found on heathland that has not become too overgrown. It is also found on both limestone and chalk grassland and was formerly found in upland mosses. This species is a warmth-loving butterfly and, as such, is often found in sheltered areas, or those that are south-facing.



Click here to see the distribution of this species or here to see the distribution of this species together with specific site information overlaid.

Life Cycle

In many colonies, especially those in the east of England and north Wales, adults start to emerge in the middle of June. Other colonies emerge later, with adults flying throughout July and, in some cases, into August. There is one brood each year.

Plebejus argus ssp. argus

Plebejus argus ssp. caernensis

The chart(s) above have been correlated with the phenology plot below, taken from the UK Butterfly Monitoring Scheme. The blue line gives average counts over the full data set from 1976 to date, and the red line gives the average for the last year.


As for the larva and pupa, newly-emerged adults are also often attended by ants which offer them some protection from predators. Unlike many other species, this blue will fly in overcast weather, so long as the temperature is sufficiently high. The adults roost communally and this can provide a wonderful sight first thing in the morning, as the adults open their wings to catch the heat from the sun's rays. Males can be observed flying low over vegetation, searching out females, which are mated very soon after emergence. Neither sex spends much time visiting flowers to nectar but, when they do, Bell Heather is a favourite nectar source.

Adults feed primarily on Heather (Calluna vulgaris / Erica spp.).

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The egg is laid singly either on the foodplant, or on surrounding vegetation or debris. Eggs are often laid close to the ground, where it is believed the higher temperature favours development. This species overwinters in this stage, the larva being fully-developed inside the egg.

Silver-Studded Blue - ovum - Unknown location - May-05 (2) [Reg Fry]

Photo © Reg Fry

Silver-Studded Blue - ovum - Thatcham - 17-Mar-07 (1009) [REARED]

Photo © Pete Eeles

Silver-Studded Blue - ovum - Unknown location - May-05 [Reg Fry]

Photo © Reg Fry

Silver studded Blue, freshly laid ovum, Bramshott Common, 24/06/2015

Photo © Pauline

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The newly-emerged larva feeds on the tenderest parts of the foodplant, including young shoots, buds and flowers. The larva is often found in the presence of ants, especially the black ant Lasius niger, which are believed to offer the larva some form of protection against parasites and other predators. Ants are attracted from secretions exuded from a Newcomer's gland at the tail end of the larva. There are 3 moults in total.

The primary larval foodplants are Bell Heather (Erica cinerea), Bird's-foot Trefoil (Lotus corniculatus), Common Rock-rose (Helianthemum nummularium), Cross-leaved Heath (Erica tetralix), Gorse (Ulex europeaus), Heather (Calluna vulgaris / Erica spp.) and Horseshoe Vetch (Hippocrepis comosa).

Silver-studded Blue - larva (4th instar) - Thatcham - 20-Apr-14 [REARED]

Photo © Pete Eeles

Silver-studded Blue - larva (4th instar) - Thatcham - 04-May-14 [REARED]-2

Photo © Pete Eeles

Silver-studded Blue - larva (3rd instar) - Thatcham - 13-Apr-14 [REARED]

Photo © Pete Eeles

Silver-studded Blue - larva (3rd instar) - Thatcham - 31-Mar-14 [Reared]-3

Photo © Pete Eeles

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Pupation takes place in a silk-lined chamber just below ground, often in an ants' nest. As for the larva, the pupa is often attended by ants, and it has been known for ants to form nests around the pupation site. This stage lasts between 2 and 3 weeks.

Silver-studded Blue - pupa - Thatcham - 23-May-14 [REARED]

Photo © Pete Eeles

Silver-Studded Blue - pupa - Unknown location - May-05 [Reg Fry]

Photo © Reg Fry

Silver-studded Blue - pupa - Thatcham - 25-May-14 [REARED]-2

Photo © Pete Eeles

Silver-studded Blue - pupa - Thatcham - 08-May-14 [REARED]-4

Photo © Pete Eeles

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Description to be completed.

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Similar Species

Common Blue

Description to be completed.


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The following links provide additional information on this butterfly.


The species description provided here references the following publications:

Barrett (1893) Barrett, C.G. (1893) The Lepidoptera of the British Islands (Vol.1 Rhopalocera).
Dennis (1977) Dennis, R.L.H. (1977) The British Butterflies - Their Origin and Establishment.
Jones (1905a) Jones, A.H. (1905) Lycaena Argus, Kirby, var. Hypochiona, Ramb., on the North Downs. Entomologist's Monthly Magazine.
Jones (1905b) Jones, A.H. (1905) The Proceedings of the Entomological Society of London.
Kluk (1780) Kluk, K. (1780) Zwierzat domowych i dzikich osobliwie kraiowych historyi naturalney poczatki i gospodarstwo.
Leach (1815) Leach (1815) In Brewster: The Edinburgh Encyclopaedia.
Linnaeus (1758) Linnaeus, C. (1758) Systema Naturae. Edition 10.
Massey (1895) Massey, H. (1895) Lycaena aegon var. corsica on the Westmoreland Mosses. Entomologist's Record and Journal of Variation.
Murray (1897) Murray, H. (1897) Plebeius aegon var. corsica in Westmoreland. Entomologist's Record and Journal of Variation.
Swainson (1827) Swainson, W. (1827) A Sketch of the Natural Affinities of the Lepidoptera Diurna of Latreille. The Philosophical magazine : or Annals of chemistry, mathematics, astronomy, natural history and general science.
Thomas (1999) Thomas, C., Glen, S.W.T., Lewis, O.T., Hill, J.K. and Blakeley, D.S. (1999) Population differentiation and conservation of endemic races: the butterfly, Plebejus argus. Animal Conservation.
Thompson (1937) Thompson, J. Anthony (1937) A new subspecies of Plebejus argus (L.). Privately published.
Tutt (1896a) Tutt, J.W. (1896) British Butterflies: Being a Popular Handbook for Young Students and Collectors.
Tutt (1909a) Tutt, J.W. (1909) Plebeius argus var. cretaceus, n. var. P.argus var. masseyi, n. var., P.argus var. corsica, Bell, and Plebeius argyrognomon var. corsica, n. var.. Entomologist's Record and Journal of Variation.
Tutt (1909b) Tutt, J.W. (1909) A Natural History of the British Lepidoptera v10 (British Butterflies v3).
Worms (1949) de Worms, C.G.M. (1949) An Account of some of the British Forms of Plebeius argus, Linn.. The Raven Entomological and Natural History Society.