Hertfordshire & Middlesex Branch

Target Species ~ Green Hairstreak (Callophrys rubi)

Green Hairstreak Callophrys rubi © photo: Trevor Chapman

Status

The Green Hairstreak is identified in the Thames Regional Action Plan as having Low Priority status There is no Species Action Plan available at present. Although identified as "Low Priority" the Green Hairstreak has been identified as a species whose status in Hertfordshire is uncertain and the species has shown significant recent declines. It is absent from Middlesex.

Behaviour and Identification

The Green Hairstreak, like most of its family, is a small butterfly whose adults fly once during the year and it is normally confined to small colonies. It is therefore a rather elusive species, often said to be difficult to see, but by hairstreak standards is quite distinctive when seen if only because it flies at a low level. The characteristic green-and-chocolate brown flickering flight is unmistakable. As it always perches with the wings closed, the green underside of the wings are visible and distinctive being of a shade of pale, slightly bluish green not often found in nature and certainly in no other British butterfly.

Individuals are usually seen in one of two possible modes. The first sightings of the season are of displaying males high in the bushes. Later sightings are usually the females flying low in search of egg laying sites usually on Rockrose but also, it has been seen to lay on Dogwood, Buckthorn, Bird's-foot trefoil, Bramble and even Cross Leaved Heath. There may be other foodplants.

Dogwood in autumn cornus sanguinea © photo: Malcolm Storey BioImages - Virtual Field-Guide (UK)	Common Bird's-foot Trefoil lotus corniculatus © photo: Malcolm Storey BioImages - Virtual Field-Guide (UK)	Rock Rose helianthemum nummularium © photo: Nigel Agar

Flight Period and Life History

The caterpillars are green and inconspicuous. It is the only British hairstreak that over-winters as a pupa. Pupation seems to be dependent on ants. The pupae, which can emit a distinct squeak, have been found in ants’ nests. The first sign of the adults in late April or early May, are of displaying males, possibly accompanied by females, high in hedges or on individual bushes, perched on leaves and periodically flying up to engage in aerial dogfights with rivals. Later, the females fly low over the low herbage and chalk grassland turf in search of an egg laying site. The flight period is normally from April to June peaking in mid May. It is therefore the earliest of the British hairstreaks and the discovery of a colony can be the first butterfly treat of the year. There is the possibility that there might be a 2nd brood in July or August as fresh individuals seen flying very late have been reported from Dorset. (Reference: British Wildlife 14/1 October 2002 page 56)

Habitats

The habitat must therefore contain both grassland and scrub. A restricting factor may be the existence of short well-cropped turf with well-established ant hills. Long unkempt grass can be unsuitable for ants and this breaks a chain in the habitat requirements for the hairstreaks. The catholic choice of food plant means that the Green Hairstreak can form colonies in a variety of habitats although in Hertfordshire, at present most known colonies are on the high chalk of the Chiltern ridge. One accidental result of this preference is that many Hertfordshire colonies straddle the borders with either Bedfordshire or Buckinghamshire which has the effect of distorting the records.

Hexton Chalk Pit © photo: Nigel Agar

Green Hairsteaks form small and discrete colonies which are sometimes scattered over a fairly wide area of a suitable habitat. They can almost certainly move through unsuitable habitat to establish new colonies. On the Telegraph/Pegsdon Hills for example a colony faithful to the lynchet area on Noon Hill failed to appear one year but a colony appeared on the other side of the Pegsdon Barns valley above a disused chalk pit. Both are on the Bedfordshire side. Sometimes the butterflies appear in the gullies on the top of Telegraph Hill and in the scrubby area known as Hoo Bit (in which case they count as Hertfordshire insects!) These locations are scattered on either side of the Beds/Herts border which can make the county records quite variable. A local extinction anywhere should not be assumed without an extensive search of nearby locations.

Pegsdon Hills © photo: Nigel Agar

Distribution in Hertfordshire and Middlesex

At present, active known colonies along the Chiltern tops are the Wood Lane area near Pirton, the Pegsdon/Telegraph Hills, occasionally at Hexton Chalk Pits, the Barton Hills, Sharpenhoe Clappers, possibly the Sundon Downs then, to the west of the Luton-Dunstable conurbation, are sites along the Whipsnade escarpment, at Ivinghoe Beacon/Ashridge, Aldbury Nowers and finally Tring Park.

Off the Chilterns, there was a colony on the verge of the A41 near Hemel Hempstead but there have been no recent sightings nor at Blackmore End, near Kimpton or Crouch End between Langley and Codicote. The known sites actually within Hertfordshire are strictly therefore the Wood Lane area near Pirton, Telegraph Hill, Hexton Chalk Pits, Tring Park and Aldbury Nowers.

Hexton © photo: Nigel Agar

Table 1: Sites where Green Hairstreak have been found since 2007

Site	Tetrad Reference
Aldbury Nowers	SP9413/SP9513
Tring Park	SP930105
Hexton Chalk Pit	TL1029
Telegraph Hill	TL1128
Wood Lane/Pirton area	TL1431

Table 2: Sites where Green Hairstreak have been found just outside Hertfordshire

Site	Tetrad Reference	County
Pegsdon Hills area	TL1229	Bedfordshire
Sharpenhoe Clappers	TL064296	Bedfordshire
Whipsnade	SP999185	Bedfordshire
Barton Hills	TL095295	Bedfordshire
Ivinghoe Beacon	SP961163	Buckinghamshire
College Lake (Tring)	SP933140	Buckinghamshire
Pitstone Hill (next to Aldbury Nowers)	SP950143	Buckinghamshire

Historic distribution

Table 3: Sites where Green Hairstreak were found 1907 - 1995 (data held by North Herts District Council Museums)

Site	Tetrad Ref.	Last seen	Site	Tetrad Ref.	Last seen
Aldbury Nowers	SP91L	Still present	Datchworth	TL21U	1971
Hudnall Common*	TL01B	1936	Bramfield Wood/Forest	TL21Y
Bricket Wood	TL10F	1907	Knebworth Woods	TL22G	1922
Symondshyde	TL11V	1951	Graveley	TL22I	1948
Wheathampstead	TL11W	1986	Little Woods	TL22X	1941
Lamer Park	TL11Y	1979	Weston Hills	TL23L	1979
Ravensburgh Castle	TL02Z	1985	Weston	TL23Q	1986
Noon Hill	TL12E	Present	Cuffley Station	TL30A	1972
Telegraph Hill	TL12J	Still present	Fanshaws	TL30J	1955
Deacon Hill	TL12J	Still present	Danemead	TL30N	1977
Hexton Chalk Pits	TL13A	Still present	Bayfordbury	TL31A	1970 & 1974
Pirton	TL13F	Still present	Brights Hill	TL32B	1986
Tingley Wood	TL13F	N/A	St. Johns Wood	TL32C	1945
Wood Lane area, Pirton	TL13F	Still present	Green Tye	TL41P	1976
Dell, Cuffley*	TL20F	1965	Stocking Plantation	TL42K	1942
Essendon	TL20T	1938	Long Meadow	TL42Q	1942
Lemsford Springs	TL21G	1979	Whippendell Woods	TQ09T	1979
Digswell	TL21H	1961	Oxhey Woods	TQ19B	1907
Mardley Heath	TL21N	1986

Distribution Map of Green Hairstreak in Hertfordshire and Middlesex

Click on map for details

SYMBOL	DATE	REFERENCE SOURCE
	2002-2004	Indicates records sent to Nigel Agar and/or reported to the HMBC Branch Website for the year 2002-2004
O	1995-2001	Indicates records taken from the Herts & Middx Butterfly Report for 1999 - John B. Murray & Rob Souter and Herts & Middx Butterfly Report for 2001 - John B. Murray & Andrew Wood
O	1970-1987	Indicates records taken from Butterflies of Hertfordshire - Brian Sawford 1987
O	1980-1986	Indicates records taken from Butterflies of the London Area - Colin Plant 1987
O	prior to 1970	Indicates records taken from Butterflies of Hertfordshire - Brian Sawford 1987