Brown Argus
This Brown Argus (Aricia agestis) is interesting because it was at an altitude of more than 1000 feet asl in the Pennines near to where I live. This butterfly used to be restricted to warm, south-facing chalk downland sites in the south where its caterpillars fed on Rock-rose. There were also a few scattered additional sites, mainly on coastal dunes but also in the Brecks where the larval foodplants were Dove's-foot Cranesbill or Common Storksbill. But in the 1990s the butterfly began to spread, utilising these other two plants. This was thought to be due to a combination of setaside (the policy of leaving some arable land fallow) plus a warming climate, as the caterpillars need warmth to develop. I searched the area thoroughly where the butterflies were and there was no Rock-rose, Storksbill nor Dove's-foot Cranesbill. But there was another Cranesbill growing abundantly; Cut-leaved Cranesbill (Geranium dissectum) which must have been the larval foodplant. This was only the second time I have seen Brown Argus locally, the other was in 2019, but that was a mere 260 feet asl, not even close to the 1089 of this colony.
One final thing, some might look at the tiny amount of white by the discal forewing spot and say this is Northern Brown Argus (A. artaxerxes salmacis), but they are invariably single-brooded and do not emerge until mid June at the earliest. Brown Argus usually has two broods, one emerging in May, the other in July. Here's the salmacis form of Northern Brown Argus showing some forewing white for comparison (taken 23 June 2018): www.flickr.com/photos/timmelling/43229942011/in/photolist
Brown Argus
This Brown Argus (Aricia agestis) is interesting because it was at an altitude of more than 1000 feet asl in the Pennines near to where I live. This butterfly used to be restricted to warm, south-facing chalk downland sites in the south where its caterpillars fed on Rock-rose. There were also a few scattered additional sites, mainly on coastal dunes but also in the Brecks where the larval foodplants were Dove's-foot Cranesbill or Common Storksbill. But in the 1990s the butterfly began to spread, utilising these other two plants. This was thought to be due to a combination of setaside (the policy of leaving some arable land fallow) plus a warming climate, as the caterpillars need warmth to develop. I searched the area thoroughly where the butterflies were and there was no Rock-rose, Storksbill nor Dove's-foot Cranesbill. But there was another Cranesbill growing abundantly; Cut-leaved Cranesbill (Geranium dissectum) which must have been the larval foodplant. This was only the second time I have seen Brown Argus locally, the other was in 2019, but that was a mere 260 feet asl, not even close to the 1089 of this colony.
One final thing, some might look at the tiny amount of white by the discal forewing spot and say this is Northern Brown Argus (A. artaxerxes salmacis), but they are invariably single-brooded and do not emerge until mid June at the earliest. Brown Argus usually has two broods, one emerging in May, the other in July. Here's the salmacis form of Northern Brown Argus showing some forewing white for comparison (taken 23 June 2018): www.flickr.com/photos/timmelling/43229942011/in/photolist