Hertfordshire & Middlesex Branch

Distribution and Status

After an absence of 60 years, the Adonis Blue has returned to Hertfordshire. It appeared to have been introduced on Therfield Heath for which the branch were not consulted, probably as pupae, in the summer of 2019 when several individuals were seen on the wing in August and September of that year. Numbers have steadily increased since then at the site but it remains to be seen if the butterfly is established here. It was also seen east of Clothall Common near the Baldock bypass in 2022. This species has never knowingly been reported in Middlesex.

Habitat Requirements

Chalk grasslands especially on closely grazed south-facing slopes with an abundance of Horseshoe Vetch Hippocrepis comosa

Larval Foodplants

Horseshoe Vetch Hippocrepis comosa, [White Clover Trifolium repens]

Adult Food Sources

Wild Marjoram Origanum vulgare, Horseshoe Vetch Hippocrepis comosa, Common Bird's-foot-trefoil Lotus corniculatus

Behaviour/Observation notes

It is a sun-loving butterfly and will fly only in sunshine when it will take nectar from Horseshoe Vetch Hippocrepis comosa in the spring but other flowers in the late summer. In early morning or evening it will often bask or roost on tall vegetation affording good photographic opportunities. Martin Johnson, a frequent visitor to the site, noted many aberrations or variations (5-10%) in 2020 whereas its close relative, the Chalkhill Blue, produced very few in spite of it being known for its many variations in the distant past

Life History

The Adonis Blue produces two generations a year with adults first emerging in May and June, and the second brood in August and September. The second brood is usually larger than the first although this is not currently the case at Therfield Heath. The eggs are laid singly on Horsehoe Vetch H. comosa leaves. Eggs hatch in 2-4 weeks with larvae from the summer brood hibernating in a silk pad on the leaf or low down on the stem. Secretions from the larvae attract the attention of ants which provide some protection from predators. Pupae can be found either on the ground covered in soil by ants or in ant nests themselves