Pingos, fritillaries and cranberries

I thought it was just another boggy marsh but these were collapsed pingos. A couple of miles from the livestock market at Bryncir (Gwynedd), in open access land at Bwlch Derwin, the marsh is a series of circles. One time domes of ice formed in a period of permafrost and still growing in colder climes such as the Northwest Territories (Canada). There they have a Pingo National Landmark, home to a quarter of the world’s pingos. The largest is 49m tall and rising at the rate of 2cm a year.

Our melted domes are now a quivering bog of sphagnum and other plants. My mission was to find the autumn flowering Devil’s-bit Scabious, and fortunately most of them were at the edge and not the centre of the pingos. I looked for the blue pom-pom flowers, poking above the grass, and then scanned down to the base to see if there was a caterpillar web, a communal sun lounger for basking caterpillars of the Marsh Fritillary.

Life is precarious for this butterfly, declining and confined to just a few places, mainly in the north and west, its prospects for expanding are bleak. The caterpillars, extremely fussy eaters, will only dine on Devil’s-bit Scabious and, with changes in the way we farm, there are less sites these days. In continental Europe they eat honeysuckle but Welsh Marsh Fritillaries won’t touch the stuff, they’d rather starve to death.

This problem is compounded by the mother butterfly, carrying a heavy load of eggs, only able to fly a hundred metres – long haul migration is not an option. Some summers, when the weather is just right, she can have a second clutch and, with a strong tail wind, might manage a thousand metres. Apart from being fussy eaters and poor fliers they are the unique host to a particular type of parasitic wasp. The odds seem stacked against them.

We scoured several acres of the site and counted 11 webs, each with about 20 caterpillars. Some were resting, while others wriggled in the sun, maybe weaving more onto their web. All seems well in this colony, at least for the time being.

The marsh is home to bulbous spiders, big hairy caterpillars, bright stripey ones, crickets, voles galore and by extrapolation, to shrews. There were masses of cranberries, their name in Welsh ‘llyg aeron’, which translates to shrew berries. 

Beacons of red, resting on mounds of moss, with leaves like thyme, easy to see, easy to pick. I picked a pocketful, boiled with sugar and a bit of water and my sauce is in the freezer. As I eat my turkey on Christmas Day I’ll think back to the pingo and everything that grows there.

YouTube of the caterpillars and the cranberries