Adonis Blue Butterfly
Fast Facts
Latin name: Polyommatus bellargus
Notable feature: Males are a vivid sky blue, while the females are chocolatey brown.
Conservation Status: Vulnerable
Where in the UK: Restricted to southern England but not found in the far south-west.
Adonis Blue Butterfly (Polyommatus bellargus) © Thomas Laroche, CC BY-ND 2.0
The Adonis Blue (Polyommatus bellargus) is a small butterfly, native to the UK. They get their name from the male’s striking blue colour, and while the females are a chocolatey brown colour, both sexes have a series of white lines that enter and cross the white fringes of the wings, which distinguishes them from other blue butterflies.
Over the spring and summer, the Adonis Blue has two broods: a spring generation peaking at the end of May/start of June, and a summer generation which tends to peak towards the end of August. The summer generation tends to be larger than the spring generation.
They are found on warm, short-grazed, south-facing slopes of chalk grassland, where their foodplant, Horseshoe Vetch grows.
- Wingspan: 3 to 4cm.
- Life span: Adults live between one and two weeks.
- Diet: The Adonis Blue caterpillars’ foodplant is Horseshoe Vetch (Hippocrepis comosa).
- Reproduction: The Adonis blue lays its egg on the underside of Horseshoe Vetch leaves, which the caterpillar will feed on once it hatches. The first-brood caterpillar pupates on the ground and emerges as an adult after about three weeks, while the second-brood overwinters as a caterpillar.
- When to see: There are two broods a year. Adults of the first brood can be seen from late April (spring weather dependent), while mid-May is more normal for a first sighting. The second brood is on the wing from around the end of July, and adults can be seen into September, sometimes even later.
- Population Trend: A mixed picture. In the latest GB Red List, this species is decreasing its range, but abundance on some sites can be very high, and it has recently re-expanded in some regions.
- Threats: A lack of management or under-management on sites is the biggest threat to this species. This may be through a lack of grazing to maintain the short warm sward the Adonis Blue requires, or the scrubbing up of chalk grassland, so the overall extent of the habitat is decreased.
- Interesting Fact: As with other blue butterflies, the Adonis Blue has a strong relationship with ants. The ants will ‘milk’ the honeydew that larvae exude and once the butterfly pupates, the ants will tend the chrysalis, burying it and protecting it from predators.
The Adonis Blue appears on the GB Red List (2022) as a ‘Vulnerable’ species. Protected under Schedule 5 of the 1981 Wildlife and Countryside Act.
In 2026, Buglife’s Chalk Lines project kicked off in the Surrey Hills National Landscape, aiming to restore and enhance chalk grassland for seven rare and threatened invertebrate species, including the Adonis Blue.
While Buglife continues to work to increase awareness of invertebrates and support nature’s recovery through our projects and campaigns, we need your help! You can support our work by joining the Buglife community. You can also join a recording scheme and log your finds – download the iRecord app and get recording!
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