A Small Tortoiseshell at Arnside Knot, Cumbria. © 2017 - 2020 Steven Cheshire.
The Small Tortoiseshell is one of our most common and easily recognised butterflies. It is fast flying in bright sunshine but can be easily approached when feeding. It hibernates during the winter and is usually one of the first butterflies to be seen on the first sunny days of spring.
Recent years have seen a rapid decline in the population of the Small Tortoiseshell butterfly across Warwickshire and the whole of the UK. One of the reasons for this decline is due to the expanding range of a tachinid parasitic fly Sturmia bella which was first recorded in Britain in 1999. The fly lays its eggs on the surface of Common Nettle leaves. These are ingested by the young caterpillars of the Small Tortoiseshell. The Sturmia bella larvae develop within the caterpillar and emerge just after the caterpillar pupates, killing the pupae in the process. This has had a devastating impact upon a once common species. However, habitat loss and pesticide use has almost certainly contributed significantly to its decline over the last 20 years.
Other nettle feeding species of the Nymphalidae family (Peacock, Comma and Red Admiral) also ingest the eggs of the Sturmia bella fly but these species appear not to be affected to the same extent as the Small Tortoiseshell.
The Small Tortoiseshell can be found in a range of habitats from urban gardens to agricultural land. It is most numerous where abundant nectar sources are available and Common Nettle the larval food plant can be found in sunny locations.
The larvae of the Small Tortoiseshell feed on Common Nettle (Urtica dioica). Males are usually seen defending patches of Common Nettle from intruders while waiting for a female to pass by with which to mate. Females are also easily observed laying eggs on the underside of a fresh nettle leaf.
Allowing a patch of Common Nettle to grow in your garden in a sunny location is a quick and easy way to encourage this species to breed. Planting nectar sources such as Buddleia and Iceplant will attract the adult butterflies, especially during the summer months.
The Small Tortoiseshell can be found throughout Warwickshire. It is a widespread species and can be numerous at times where suitable habitat allows.