Gardens aflutter with Small Tortoiseshells

No.:  2013-31
September 2013

The long spell of hot, dry weather seems to have reversed the damage done by last year’s wet summer, and our butterflies are making the most of it. As the British Trust for Ornithology’s (BTO) Garden BirdWatch data show, none has responded more dramatically than the Small Tortoiseshell.

Small Tortoiseshell by Dawn Balmer/BTO

The Small Tortoiseshell is one of the most
widespread butterflies in the UK

It was touch and go for our butterflies, after last year’s wet summer and this year’s cold spring. However, the hot, dry weather at the beginning of July was a turning point for many species, including the Small Tortoiseshell. Although their numbers normally increase at the end of the summer, with new butterflies emerging from the second brood, the BTO’s Garden BirdWatch reporting rate has exceeded expectations for this time of year, and is double that seen this time last year.

A familiar butterfly to many of us, the Small Tortoiseshell is one of the most widespread butterflies in the UK, ranging from the lowlands of England to the Scottish islands and highlands. Despite having suffered a slight decline in abundance since the 1970s, Small Tortoiseshells are still a common sight, and their numbers seem to have stabilised in recent years.

This year’s boost for Small Tortoiseshells is probably due to three reasons. Firstly, the long period of dry, hot weather has been good for both butterflies and the flowering plants they feed on. Secondly, there may have been an influx of immigrant Small Tortoiseshells from continental Europe, making the most of the warm weather and boosting our UK population. Finally, it is possible that the parasitic fly Sturmia bella, which is thought to be a partial cause of the overall decline of Small Tortoiseshell, is currently at a low point in its population cycle.

Clare Simm, Garden BirdWatch Development Officer says: "At this time of year, Small Tortoiseshells are feeding up before going into hibernation during the colder months. They love nectar-rich flowers and, in gardens, can be found on plants such as Buddleia, Valerian, Hebe and Michaelmas daisies."

She added: "Once the weather starts to cool, Small Tortoiseshells will begin to look for somewhere warm to hibernate, which may include your house. If you find a Small Tortoiseshell, or any other butterfly species, in your house, don’t leave it there. Once the central heating turns on, it will wake up from hibernation and use up valuable food reserves. However you should also avoid putting it outside as the cold will kill it. The ideal thing to do is to ‘rescue’ it and place it in an unheated outbuilding or shed. The temperature will remain more stable there and the butterfly should successfully hibernate until the weather becomes warmer again."

Notes to Editors

  1. The BTO Garden BirdWatch is the only nationwide survey of garden birds to run weekly throughout the year, providing important information on how birds use gardens, and how this use changes over time. Currently, some 14,500 people take part in the project. The project is funded by participants’ contributions and is the largest year-round survey of garden birds in the world. For more information see www.bto.org/gbw.
  2. For more information on the Small Tortoiseshell butterfly, please look here and on the GBW Homepage here.
  3. The BTO is the UK's leading bird research charity. A growing membership and up to 60,000 volunteer birdwatchers contribute to the BTO's surveys, collecting information that underpins conservation action in the UK. The BTO maintains a staff of 100 at its offices in Thetford, Stirling, Bangor (Wales) and Bangor (Northern Ireland), who analyse and publicise the results of surveys and projects. The BTO's work is funded by BTO supporters, government, trusts, industry and conservation organisations. www.bto.org

Contact Details

Clare Simm
(GBW Development Officer)

Office: 01842 750050
(9am to 5.30pm)
Email: clare.simm [at] bto.org

Paul Stancliffe
(BTO Media Manager)

Office: 01842 750050
(9am to 5.30pm)
Mobile: 07585 440910 (anytime)
Email: press [at] bto.org

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