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 the county 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-plant 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.
This year however, there has been a veritable ‘tidal wave’ of Sussex Emeralds, with around 20 individuals trapped behind the temporary Visitor Centre between 7th and 21st of July and with a maximum of eight on the 11th. It seems highly likely that the species is breeding at Rye Harbour this year, though we will only know for certain if we find larvae on the reserve. While larvae are present in late summer they are very small and difficult to find (very few of these late summer larvae have ever been found in the UK), so it will have to wait until May 2020 when they will have grown to more ‘findable’ proportions. Probably the best place to look for it will be on the damaged shingle habitats inside the rabbit-fenced exclosures at the western side of Flat Beach. For many years this area was a ‘sea’ of non-native Red Valerian, but a program of removal followed by spreading of Wild Carrot seeds has now made it suitable as Sussex Emerald breeding habitat, so fingers crossed!