As the Adonis blue (Polyommatus bellargus) uses Horseshoe vetch (Hippocrepis comosa) as its larval food plant, it can only be found where that species of vetch grows, which in turn means the majority of this butterfly’s colonies are restricted to certain locations in southern England, specifically ‘in the core areas of chalk downland in Dorset, Wiltshire, Sussex and the Isle of Wight’, according to Life Cycles of British & Irish Butterflies. (Horseshoe vetch will feature in tomorrow’s blog post.)

The restriction imposed by its larval plant means I never see this butterfly in Wales, and so, last week, on the Isle of Portland, was only the fourth time I’d seen the stunning cobalt blue upper wings of the male Adonis blue.

And, as this was the very start of their 2026 season – there are two generations of adults each year, the first fly in May-June, the second in August-September – I only saw three individuals, all males. The females emerge a little later than the males, so, due to poor timing on my part, I’ve only once seen a female Adonis blue, back in August 2019, during a visit to the Malling Down Reserve in East Sussex. Though I already have another trip to Weymouth and Portland booked, that will be in July, so I will once again miss seeing any females. I intend trying to remedy that omission next year, as I would very much like to be present when more of these little stunners are in flight, both male and female.