Every week since April we have been recording butterflies at Embsay reservoir as part of the UKBMS (UK Butterfly Monitoring Scheme).  

The survey starts with week 1 on the 1^st of April and will finish with week 27 at the end of September. While the survey is of adult butterflies, this week we were also pleased to see lots of small tortoiseshell and red admiral, along with a few peacock, caterpillars (see butterfly counts and photos).

These were all along the side of the causeway between the South side of the reservoir and the steep bank towards the water treatment plant.

All of the caterpillars (larvae) we saw recently were feeding on the nettles growing along the side of the track. Nettles are their only food plant, so none of these beautiful butterflies can survive without them. It was for this reason that we were dismayed in late June when all of the vegetation along the track was strimmed.

As shown in the photographs, the peacock and small tortoiseshell larvae are found in colonies. In contrast, red admiral caterpillars occur singularly and make a cocoon by rolling up a nettle leaf, presumably to protect them from predators. Both peacock and small tortoiseshell survive the winter as adults so the larvae must pupate and undergo metamorphosis before the weather turns too cold. Red admiral migrate South to the continent to overwinter, so they too must reach adulthood to survive winter.  With the subsequent crop of new nettles now growing along the causeway, and along with them caterpillars, we are hopeful that some of this new generation will survive to adulthood and appear again next year.

If you have any questions or comments about this article, please contact Ian at devilsbit18@gmail.com.  Thanks to everyone who has helped with the transect this year. Photographs by Barbara Blomfield.

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