Small Tortoiseshell (Aglais urticae)

The Small Tortoiseshell is one of our most-familiar butterflies, appearing in gardens throughout the British Isles. Unfortunately, this butterfly has suffered a worrying decline, especially in the south, over the last few years. This butterfly has always fluctuated in numbers, but the cause of a recent decline is not yet known, although various theories have been proposed. One is the increasing presence of a particular parasitic fly, Sturmia bella, due to global warming - this species being common on the continent. The fly lays its eggs on leaves of the foodplant, close to where larvae are feeding. The tiny eggs are then eaten whole by the larvae and the grubs that emerge feed on the insides of their host, avoiding the vital organs. A fly grub eventually kills its host and emerges from either the fully-grown larva or pupa before itself pupating. Although the fly attacks related species, such as the Peacock and Red Admiral, it is believed that the lifecycle of the Small Tortoiseshell is better-synchronised with that of the fly and it is therefore more prone to parasitism. This is one of our most widespread butterflies, occurring throughout the British Isles, including Orkney and Shetland.