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  • Writer's pictureAlistair

How many ecologists does it take to find one pesky little (Marsh Fritillary) caterpillar?

I was delighted to host a team from Radnorshire Wildlife Trust ( today. They have recently acquired Pentwyn, a farm on their patch with a plan to make it a beacon for nature recovery in Radnorshire, which is really exciting. They were keen to see what we’d been up to at Cefn Garthenor and it was a great opportunity for me to get a load of knowledgeable people on site. Rob Parry (INCC and Robert Jones (my farming neighbour) were both on site, which is a good job as they have both contributed hugely to what is being achieved and, unlike me, actually know what they are talking about.

Walking our visitors around was a great reminder of how lucky we are with the sheer diversity of habitat here. Marshy grassland, wet woodland, broadleaf woodland, bits of wet heath and more, including the inevitable so-called improved grassland. They were able to see the work we have started to shift the improved grassland fields towards being wildflower meadows, the ponds and scrapes we’ve created and the work that the Galloway cattle have done to open up the opportunities for greater diversity.

However, after lunch the fun was over and it was time to put our visitors to work. Rob was keen to find out if our Devil’s Bit Scabious had attracted any Marsh Fritillary butterflies. At this time of year that would mean caterpillars munching away. So, we put the RWT team to search the marshy grassland. No one believes me when I say “don’t bring walking boots, bring wellies … no matter how many dry weeks we’ve had”. However, they were a hardy bunch, got stuck in and pretty soon were over their boots in boggy heath.

(L to R, getting stuck in, field vole food pile, water vole latrine)

In the first area, part of our SSSI area below the bridleway, we found the wrong type of caterpillar with a collection of rather beautiful Scarlet Tigers. We also found signs of both Field Voles (with little, messy, food piles in the soft rush) and also Water Voles (latrines on their pathways).

(L to R: wood anemones, lousewort and marsh marigolds)

Undeterred, we moved to the north of Cefn Garthenor, still in the SSSI, and finally, after checking out the Marsh Marigolds, Wood Anemones and Lousewart found the proverbial needle in the haystack in the form of a little Marsh Fritillary caterpillar sunbathing near some Devil’s Bit Scabious.

(L to R: flamboyant but common scarlet tiger caterpillar, the elusive marsh fritillary caterpillar)

Rob was very, very happy! The Marsh Frit is threatened not only in the UK but across Europe, and Rob’s charity, INCC, have been working hard to conserve them (Saving the Marsh Fritillary in South Wales – Initiative for Nature Conservation Cymru).

A potential problem going forward is that, if successful in our area, the Marsh Fritillary caterpillars could eat all the Devil’s Bit Scabious, its source of food, and eventually wipe itself out. Fortunately (and I use that word somewhat hesitantly) there is a parasitoid wasp (even rarer than the butterfly) which, if present, keeps a cap on numbers through its habit of injecting eggs into the caterpillars. The caterpillars live on, as kind of zombies, but never mature into butterflies, so saving the Devil’s Bit Scabious for future generations (from those that avoid zombification). Nice.

Job done, we released the Radnorshire Wildlife Trust team back to their native Llandrindod Wells.


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