Small Tortoiseshell

Aglais urticae — the small tortoiseshell — is one of the most familiar European garden butterflies and a flagship species of British and European butterfly identity. The species is widespread across Europe, North Africa, and into central and eastern Asia. Adults reach 4-5 cm wingspan with bright orange-and-black upperside wings carrying a distinctive row of blue spots along the wing margins. Underside is dark mottled brown — perfect dead-leaf camouflage when wings are folded at rest. The species overwinters as adults in cool dark sheltered places (garden sheds, attics, hollow trees, rock crevices) and is one of the very first butterflies to fly each spring across Europe — often the year's first butterfly seen in February-March warm spells. Caterpillars are bright black with yellow side stripes and feed gregariously on stinging nettle (Urtica dioica), forming dramatic communal silken nests on host plants in summer. The species was historically the most-encountered garden butterfly across most of Europe, but UK populations have declined dramatically since the 2000s — by approximately 80% across many southern English counties (Butterfly Conservation UK). The cause of decline is poorly understood and a subject of active research; one leading hypothesis is the increased prevalence of the parasitoid tachinid fly Sturmia bella, which spread northward into Britain since the 1990s and parasitizes small tortoiseshell caterpillars at high rates.