The Sussex Emerald (Thalera fimbrialis) moth is a very rare beast in the UK, with breeding traditionally restricted to the disturbed shingle habitats at Dungeness in Kent (though it has colonised two other sites further east in Kent in recent years). Adults are active between July and early August and the eggs are laid (and the larvae usually feed) on Wild Carrot, though both Common Ragwort and Hoary Ragwort (and more rarely Yarrow and Gorse) are utilised as a secondary food-plants in the UK. As its name suggests, this species was first found in the UK in Sussex and there were several records around the Beachy Head / Eastbourne area prior to the 1950s. Since then it has occurred only as an occasional immigrant and at Rye Harbour previous to 2019 there had only been two records, with singles on two dates in July 2010.
Initially, management to encourage this species at Rye Harbour began with the removal of large swathes of Red Valerian which had come to dominate, followed by the by collection and spreading the seeds of Wild Carrot at various points around the reserve, but particularly within the fenced rabbit exclosures on the Beach Reserve, the habitat most similar to that found at its traditional breeding sites in Kent.
Sean Clancy and Rebecca Levey, with Discovery Centre in background
This effort appears to have paid off and from 2019 adult moths became relatively abundant in the moth trap, with a total of 22 trapped in 2019 and 15 in 2020 and there was a strong suspicion that this species was breeding at Rye Harbour. A search for larvae in May 2020 was unsuccessful, but a return visit by moth expert Sean Clancy and Rebecca Levey of ‘Kent’s Magnificent Moths’ (https://butterfly-conservation.org/our-work/conservation-projects/england/kents-magnificent-moths) on 10th June found two well-grown larvae on Wild Carrot in the grassy area just to the west of the temporary visitor centre, the first ever found in Sussex. At last, the Sussex Emerald really does live up to its name!
The first Sussex Emerald Larva ever found in Sussex