Why is the Small Tortoiseshell Declining?

Photo (c) Jim Asher

Many people have noticed dramatically reduced numbers of small tortoiseshell butterflies (Aglais urticae) in the UK over the last few years. Butterfly Conservation has become concerned that a newly-colonised parasitoid fly, Sturmia bella, may be causing widespread mortality to small tortoiseshell caterpillars in southern Britain, providing a possible explanation for the butterfly's decline.  To investigate the effects of Sturmia bella,  We are hoping to collect data from as many localities as possible across the UK, and we are linking information on the frequency of parasitism from Sturmia bella and other parasitoids to information from the UK Butterfly Monitoring Scheme on trends in butterfly population sizes. This work is being carried out in collaboration with Butterfly Conservation.

New!  Click here to read our 5-page report on the results so far, thanks to the efforts of our 2008 volunteers.

New!  Click here to watch a  7-minute BBC 'Inside Out' Film on the Small Tortoiseshell research, featuring Martin Warren and Owen Lewis

New!  Click here to read an Oxford University 'Science Blog' on our research.

You may also be interested in newspaper articles in the Independent (29 March 2008) and in the Guardian (27 April 2009)  highlighting the decline of the Small Tortoiseshell butterfly.

Summary of results so Far

A fuller summary of the results is available here.

How to join in

We are asking volunteers to collect batches of wild larvae of Small Tortoiseshell and Peacock butterflies this summer, and to rear them to determine how many die from parasitism. Emerging butterflies can be released into the wild, and any emerging parasitoid pupae or adults should be sent to us for identification. Please follow the links below for further information on taking part (Word documents):

Protocol for volunteers with full details on the study

Recording sheets

Habitat codes

Please Click Here if you are sampling in Lancashire or Cumbria

 

These documents are also available in pdf format:

 

Protocol for volunteers with full details on the study

Recording sheets

Habitat codes

Please Click Here if you are sampling in Lancashire or Cumbria

 

For further information, please contact Owen Lewis and Sofia Gripenberg