Living here in Dorset it easy to forget that the Adonis blue is one of Britain's rarest butterflies as there are times in summer on some chalk downs where the most common blue butterfly you will see is the Adonis; there are certainly three reasons why this is so. Firstly, the Adonis blue is primarily a European species and we are right at the northern edge of this butterfly's range and it would struggle to survive any further north. Next, Dorset has a substantial amount of the specific chalk downland habitat it requires to survive and lastly considerable conservation effort goes in to managing the ideal habitat requirements they need of short, grazed, flower rich turf with lots of horseshoe vetch.
The Adonis blue has two broods each year. The first emerges in mid May and flies until the end of June and then the second brood emerges in early August and flies until the end of September. There are sixty two reports of Adonis in the Nature of Dorset database for 2017 and 2018 and they show the first Adonis as being seen in week 17 in late April which is somewhat earlier than the textbooks indicate so one wonders if there is a case of mistaken identity. There are, however, very few blue species likely to be seen so early and so the report is probably correct. Reports continue until week 23 in late June and then, true to form, there is a gap until week 29 at the beginning of August. From week 29 there are then reports nearly every week until week 32 in mid October; somewhat later then might be expected. The peak of sightings are undoubtedly in August in weeks 33,34 and 35.
There are reports from 29 sites with most locations along the Purbeck coast reporting good numbers of them. They also occur along the Purbeck ridge between Lulworth and Swanage and on Portland in Tout Quarry. From Portland they can be found at various locations north eastwards along the chalk ridge to the Wiltshire border near Cashmoor. Looking at the distribution map you can clearly see which parts of Dorset are chalk or limestone!