Hertfordshire & Middlesex Branch
Saving butterflies, moths and our environment
Common at chalk sites
Distribution and Status
The Chalkhill Blue frequents chalk grasslands as the name suggests in north and west Hertfordshire. By the 1980s the only known significant colony was at Therfield Heath but even there it was just surviving. However, with conservation efforts involving selective grazing at suitable sites across Hertfordshire, the butterfly has recovered well with the best colonies at Therfield Heath and Hexton Chalk Pit but it can also be found at Telegraph Hill, Aldbury Nowers, Clothall Common near Baldock and Wilbury Hill near Letchworth. The high abundance in 2013 meant some dispersal took place among male specimens where they were discovered miles away from the chalk
Habitat Requirements
Chalk grasslands especially on south-facing slopes
Larval Foodplants
Horseshoe Vetch Hippocrepis comosa
Adult Food Sources
Wild Marjoram Origanum vulgare, Field Scabious Knautia arvensis, Common Knapweed Centaura nigra. Dung
Behaviour/Observation notes
It is a conspicuous butterfly with its milky-blue appearance. During spells of sunshine it flies rapidly just above the ground in between basking and feeding. In dull weather or during early morning or evening it will often bask or roost on tall vegetation affording good photographic opportunities
Life History
The Chalkhill Blue produces one generation a year with adults starting to emerge in July and peaking around the end of the month into the first week of August. Eggs are laid singly on Horsehoe Vetch H. comosa stems or surrounding vegetation. Eggs hatch in spring in the following year. Secretions from the larvae attract the attention of ants which provide some protection from predators. It is thought that pupae are often buried by the ants in the earth
Further information
Photo gallery
Branch Annual Report (2023)
UK distribution map
Full list of larval hostplants (Lycaenidae)
Stevenage butterflies - additional notes
Account for 2022