Old records of butterfly sightings revealed the possibility of a previously unknown butterfly species living in the barren moorlands of the upper Ystwyth valley. Unlike the Arran Brown, another species that defies satisfactory explanation, there are no examples to be found in the cabinets housing Victorian butterfly collections. It was said to closely resemble the Apollo butterfly, familiar to those who are familiar with Alpine species. It differs in two respects. The hind wings have a greenish sheen caused by the mottling of that colour on the underside, while more remarkably, the red spot on those wings has been said to resemble a Welsh dragon shape. In this respect the Welsh Apollo mimics the Welsh flag. Coincidence?
Now a conservation group, Parnassius yswythii - Diogelu Rhywogaeth Ucheldir (PYDRU), Parnassius yswythii - Protect Highland Species claim to know of a small colony of the butterfly. These stamps form part of an awareness campaign to help preserve and enlarge this colony. They hope to be able eventually have a specimen available for scientific study and have Parnassius yswythii identified as a species in its own right, and add it to the British list.