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Earlier in the year, researchers from the University of Exeter’s Environmental & Sustainability Institute (ESI) conducted surveys and research on the Marsh Fritillary butterfly on the Lizard (see  http://www.the-lizard.org/index.php/article-archives/butterflies-moths/513-butterfly-surveys-in-march-your-help-pleas).
The larvae were found on 5 sites, but because this butterfly is so rare nationally, the Lizard populations are now very important at both the county and country level. However, they were not found on one small site which they were known to frequent until very recently.


A small cluster of larvae in early springA small cluster of larvae in early spring. ©Chloe Lumsden

Although the numbers of webs found were quite encouraging, butterfly populations can fluctuate dramatically between years. Weather is one of the most important factors, especially during the flight period when females rely on suitable weather to search for Devils-bit scabious plants on which to lay their eggs.
However, many species of butterfly are also parasitised, including the Marsh fritillary. The white cotton-bud like cocoons of a wasp parasitoid (of the genus Cotesia) was found across all 5 of the Marsh fritillary sites on the Lizard.
The wasp like parasitoid Cotesia on top of a cocoon adjacent to an infected Marsh fritillary larvae.
The wasp like parasitoid Cotesia on top of a cocoon adjacent to an infected Marsh fritillary larvae. ©Peter Eeles

A larval web around  Devils-bit scabious
A larval web around Devils-bit scabious ©Peter Eeles

While many people take an instant dislike to this species (it is obviously not as conspicuous or attractive as the butterfly!), it should also be remembered that it is considerably rarer than its butterfly host, and remarkably is often in turn parasitised by a wingless ant-like species (of the genus Gelis). Furthermore, there is no evidence to suggest that parasitoids are a serious factor in butterfly declines, especially compared to the threats posed by habitat destruction, fragmentation and climate change.
This autumn the University of Exeter is continuing to monitor populations of the Marsh fritillary on the Lizard, with the aim of advising on management across the 5 remaining sites. Throughout August and September, Marsh fritillary larvae form large, distinctive webs around Devils-bit scabious plants (below). If you see some larvae whilst out walking over the next month or so, please could you inform Robin Curtis at ESI (This email address is being protected from spambots. You need JavaScript enabled to view it.), providing a date, location and preferably a photo - all records will remain confidential.

Published: July 2015
Author: Robin Curtis (Researcher, Exeter University)