Chalk Hill Blue

Polyommatus coridon (po-lee-oh-MAY-tuss KO-ri-don)

Chalk Hill Blue male - Springhead, Sussex 15-July-2014
Photo © Neil Hulme
 

Wingspan
33 - 40mm

Checklist Number
61.020

Family:LycaenidaeLeach, 1815
Subfamily:PolyommatinaeSwainson, 1827
Tribe:PolyommatiniSwainson, 1827
Genus:PolyommatusLatreille, 1804
Subgenus:LysandraHemming, 1933
Species:coridon(Poda, 1761)

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Introduction

As its name suggests, the Chalk Hill Blue is found on chalk downland, although limestone downland is also used. The adult butterfly is most-often seen in bright sunshine, where the ground may appear to shimmer with the activity of hundreds, if not thousands, of males searching for a mate just a few inches above the ground. The distribution of this species follows the distribution of Horseshoe Vetch which, in turn, follows the distribution of chalk and limestone grassland. This species is therefore restricted to England, south east of a line running from West Gloucestershire in the west and Cambridgeshire in the east. This species is absent from most of central England, northern England, Scotland, Wales, Ireland, the Isle of Man and the Channel Islands.

Polyommatus coridon

This species was first defined in Poda (1761) as shown here (type locality: Graz, Austria).

Male Chalkhill Blue, Oxenbourne Down, 20 July 2012

Male
Photo © Pauline

Chalkhill Blue - Hatch Hill - Somerset - 31/07/14

Male Underside
Photo © William

Chalkhill Blue (female), Springhead Hill (20 July 2012)

Female
Photo © Mark Colvin

Chalkhill Blue, female, Stockbridge Down, 06/08/2013

Female Underside
Photo © Pauline

Photo Album ...


Conservation Status

Weather patterns over the last decade or so have not been kind to the Chalkhill Blue and, even though the population trend is one of increase, there is a worrying decline in distribution. This is therefore a butterfly of conservation concern.

UK BAP StatusDistribution Trend (%)Population Trend (%)
Species of Conservation Concern
Stable-1
Decrease-26

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).

Habitat

This species lives in discrete colonies where its foodplant, Horseshoe Vetch, is found in abundance. It is also a warmth-loving butterfly, and is typically found on sheltered, south-facing hillsides.

Distribution

 

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

There is one brood each year with the adults emerging in mid-July in typical years, a peak being reached at the end of July and early August.

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.

Imago

The sexes are strongly dimorphic; the males being a pale sky blue, and the females being a chocolate brown. The adults use a variety of nectar sources, and the males will also visit, often in some numbers, moist earth or animal droppings to gather salts and minerals.

At good sites, this species can be found roosting communally on grass stems at the lower slopes of a hillside, occasionally with several individuals on the same stem. This is a highly-variable butterfly and many named aberrations of this species exist.

Adults feed primarily on Bird's-foot Trefoil (Lotus corniculatus), Carline Thistle (Carlina vulgaris), Field Scabious (Knautia arvensis), Selfheal (Prunella vulgaris), Thistles (Cirsium spp. and Carduus spp.) and Thyme (Thymus polytrichus).

Polyommatus coridon

Chalkhill Blue - imago - Stockbridge Down - 19-Jul-07 (1095)

Photo © Pete Eeles
19-Jul-2007

Chalkhill Blue - imago - Stockbridge Down - 22-Jul-11 (2)

Photo © Pete Eeles

Chalkhill Blue - imago - Stockbridge Down - 24-Jul-14

Photo © Pete Eeles
24-Jul-2014

Chalkhill Blue Pair - Colley Hill, Reigate, Surrey 9-Aug-11

Photo © Vince Massimo
09-Aug-2011

Chalkhill Blue - imago - Stockbridge Down - 12-Jul-09 (6)

Photo © Pete Eeles
12-Jul-2009

Chalkhill Blue - imago - Stockbridge Down - 20-Jul-10 (1)-2

Photo © Pete Eeles
20-Jul-2010

Chalkhill Blue - imago - Stockbridge Down - 12-Jul-09 (3)

Photo © Pete Eeles
12-Jul-2009

Chalkhill Blue - Stockbridge Down - 11 Aug 2010 (1)

Photo © Clive
11-Aug-2010

Chalkhill-Blues, Draycott 27.08.2015

Photo © Chris Gladman

Chalkhill Blue - imago - Stockbridge Down - 06-Aug-09 (3)

Photo © Pete Eeles
06-Aug-2009

Chalkhill Blue - imago - Stockbridge Down - 20-Jul-10 (3)

Photo © Pete Eeles
20-Jul-2010

Chalkhill Blue (female), Springhead Hill (20 July 2012)

Photo © Mark Colvin
20-Jul-2012

Chalkhill-Blue-Newmarket 24 July 2011 03C1356

Photo © IainLeach

Chalk Hill Blue male - Springhead, Sussex 15-July-2014

Photo © Neil Hulme
15-Jul-2014

Chalk-Hill-Blue- 5D32600. Surrey, July 2015.

Photo © IainLeach

Male Chalkhill Blue, Oxenbourne Down, 20 July 2012

Photo © Pauline

Chalkhill-Blue-Newmarket 24 July 2011 03C1330

Photo © IainLeach

Chalkhill Blue male - Aston Rowant July 21st 2012.

Photo © Nigel Kiteley
21-Jul-2012

Chalkhill Blue, Oxenbourne Down, 6/08/2012

Photo © Pauline
06-Aug-2012

Chalkhill-Blue- 5D30309 Newmarket Aug 2013

Photo © IainLeach

Photo Album ...


Ovum

Eggs are laid singly either directly on a stem of the foodplant or in nearby vegetation. Like many other Lycaenids, the female butterfly will often crawl among the vegetation, searching for suitable egg-laying sites, before finally laying a single egg. This species hibernates as a fully-formed larva within the egg, the egg stage lasting up to 8 months.

Chalkhill Blue - ovum - Stockbridge Down - 14-Aug-88 [Tim Norriss]

Photo © Tim Norriss

Chalkhill Blue - ovum - Thatcham - 26-Mar-11 (1) {REARED}

Photo © Pete Eeles

Chalkhill Blue - ovum - Thatcham - 26-Mar-11 (2) {REARED}

Photo © Pete Eeles

Chalkhill Blue ovum

Photo © Tony Moore
08-Sep-2013

Chalkhill Blue Ovum - Hatch Hill - 31/07/13

Photo © William
31-Jul-2014

Photo Album ...


Larva

On emerging from the egg, the nocturnal larva initially feeds by grazing the surface of the leaf, often from the underside, but leaves the epidermis of the opposite side of the leaf intact. During the day the larva is concealed at the base of the foodplant. Like many other Lycaenid larvae, the Chalk Hill Blue has a Newcomer's gland on the 7th segment, the secretions from which are highly attractive to ants which then afford the larva some protection against predators. The larval stage lasts between 9 and 10 weeks.

The primary larval foodplant is Horseshoe Vetch (Hippocrepis comosa).

Chalkhill Blue - larva - Stockbridge Down - 12-Jun-04 (2)

Photo © Pete Eeles
12-Jun-2005

Chalkhill Blue - larva - Stockbridge Down - 12-Jun-04 (3)

Photo © Pete Eeles
12-Jun-2005

Chalkhill Blue - larva - Stockbridge Down - 12-Jun-04 (4)

Photo © Pete Eeles
12-Jun-2005

Chalkhill Blue - larva - Stockbridge Down - Jun-88 (2) [Tim Norriss]

Photo © Tim Norriss

Chalkhill Blue - larva - Stockbridge Down - Jun-88 (3) [Tim Norriss]

Photo © Tim Norriss

Chalkhill Blue - larva - Stockbridge Down - Jun-88 [Tim Norriss]

Photo © Tim Norriss

Chalkhill Blue - larva - Unknown location - Unknown date [Brian Clegg]

Photo © Brian Clegg

Chalkhill Blue - larva - Thatcham - 18-Jun-13 (1) [REARED]

Photo © Pete Eeles
18-Jun-2013

Chalkhill Blue - larva - Thatcham - 18-Jun-13 (2) [REARED]

Photo © Pete Eeles
18-Jun-2013

Chalkhill Blue - larva - Thatcham - 18-Jun-13 (3) [REARED]

Photo © Pete Eeles
18-Jun-2013

Chalkhill Blue - larva - Thatcham - 18-Jun-13 (4) [REARED]

Photo © Pete Eeles
18-Jun-2013

Chalkhill Blue - larva - Thatcham - 30-Jun-13 (1) [REARED]

Photo © Pete Eeles
30-Jun-2013

Chalkhill Blue - larva - Thatcham - 30-Jun-13 (2) [REARED]

Photo © Pete Eeles
30-Jun-2013

Chalkhill Blue - larva - Thatcham - 30-Jun-13 (3) [REARED]

Photo © Pete Eeles
30-Jun-2013

Chalkhill Blue - larva (1st instar) - Thatcham - 20-Mar-14 [Reared]

Photo © Pete Eeles
20-Mar-2014

Chalkhill Blue - larva (1st instar) - Thatcham - 22-Mar-14 [Reared]-5

Photo © Pete Eeles
22-Mar-2014

Chalkhill Blue - larva (1st instar) - Thatcham - 22-Mar-14 [Reared]-8

Photo © Pete Eeles
22-Mar-2014

Photo Album ...


Pupa

The pupa is formed on the ground below the foodplant. Like the larva, the pupa produces secretions that ants find attractive. It is believed that ants will carry pupae away and bury them in the earth. This stage lasts approximately 4 weeks.

Chalkhill Blue - pupa - Thatcham - 04-Aug-13 (1) [REARED]

Photo © Pete Eeles
04-Aug-2013

Chalkhill Blue - pupa - Thatcham - 04-Aug-13 (2) [REARED]

Photo © Pete Eeles
04-Aug-2013

Chalkhill Blue - pupa - Thatcham - 13-Jul-13 (1) [REARED]

Photo © Pete Eeles
13-Jul-2013

Chalkhill Blue - pupa - Thatcham - 13-Jul-13 (2) [REARED]

Photo © Pete Eeles
13-Jul-2013

Photo Album ...


Aberrations

Description to be completed.

Click here to see the aberration descriptions and images for this species.

Similar Species

Adonis Blue

The female Adonis Blue is easily mistaken for a female Chalk Hill Blue and the two species occasionally fly together toward the second half of August on some sites. Distinguishing the two is not at all easy. One guideline is that the pale scales on the hindwings, between the red dots and the white fringe, are blue in a female Adonis Blue, and white in a female Chalk Hill Blue.


Adonis Blue female (left) and Chalk Hill Blue female (right)

Brown Argus

Description to be completed.

Common Blue

Description to be completed.

Northern Brown Argus

Description to be completed.

Videos


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The following links provide additional information on this butterfly.

References

The species description provided here references the following publications:

ReferenceDetails
Hemming (1933) Hemming, F. (1933) Holarctic Butterflies: Miscellaneous Notes on Nomenclature. The Entomologist.
Latreille (1804) Latreille, P.A. (1804) Nouveau Dictionnaire d'Histoire Naturelle.
Leach (1815) Leach (1815) In Brewster: The Edinburgh Encyclopaedia.
Poda (1761) Poda von Neuhaus, N. (1761) Insecta musei Graecensis.
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.