Marsh Frits – larvae web count at Rhos Cefn Bryn!

Rhos Cefn Bryn comprises of 2 fields near Llannon. On initial inspection they don’t look particularly interesting. However this site is home to 2 important Carmarthenshire species: Dormouse and Marsh Fritillary. Both species have conflicting habitat requirements, so our main job is in keeping an equilibrium so both species needs are satisfied. But at this time of year, the most important part is surveying for larval webs! And this year, our hard work seems to have paid off..

The site comprises of marshy grassland habitat surrounded by mature hedgerows, and is a good example of what this area of Carmarthenshire would have looked like before agriculture became mechanised.

Monitoring for Marsh Fritillaries takes place early September when the caterpillars are most visibly living in colonies within webs. Numbers can fluctuate widely and indeed last year we only found 1 web. This year, after a fallow year, we counted 47 webs.

Marsh frits anecdotally have been seen to increase on the odd year when no grazing occurs, this is something we have incorporated at Rhos Cefn Bryn, and every 4th year is a fallow year. 47 webs is the highest number observed since 1996!

It is always tricky to know exactly what went right this year for this species, but good weather during the main flight period in June and a relax on the grazing does seem to have helped.

We’ve also had some good results for dormouse monitoring within the hedgerows surrounding the fields. With the help of a local ecologist we are trailing a new survey technique, dormouse tracking tunnels. This method involves looking at footprints.

Out of the 25 tunnels set up, we discovered dormouse footprints on 11 within 2 weeks of being set up. This level of activity helps us understand the size of population and its distribution across the site.

-- Stephanie Coates, Wildlife Trust Officer, Brecknock

Marsh Fritillary by Mike Clark
Dormouse footprints by Stephanie Coates