Rare moth on the move

Olive crescent caterpillar

The Olive Crescent has always been rare in Britain. It used to be known from a few sites in the Chilterns and from the RSPB’s Stour Woods reserve in north Essex but the Chilterns colonies died out, leaving just one colony in the country.

Butterfly Conservation and RSPB staff carried out research into the ecology of the moth at Stour Woods to ensure that the management there was suitable. Remarkably, the larvae of the moth feed on dead leaves – and not just recently dead leaves but ones so old that they crumble in your fingers when you try to unfurl them! We found that they had a distinct preference for leaves that were hanging under the canopy of the trees, rather than ones that were exposed to the sun.

Olive Crescent mothThe Olive Crescent is known to occasionally migrate from the continent and in 2003 it was discovered in the far east of East Sussex. Several colonies quickly established in this area and by 2010 it has spread as far west as Beachy Head. Last year a single adult was seen at the Sussex Wildlife Trust reserve at Eridge Rocks, just south of Tunbridge Wells so earlier this summer, with advice from BC, staff there and at the adjacent RSPB Broadwater Warren reserve hung up cut branches within the woodland in the hope that we could find larvae in the autumn.

Last week a team of staff and volunteers from all three organisations carried out a search of the dead leaves on the hanging branches and found at least 8 larvae at Broadwater Warren and 3 at Eridge Rocks, making this the most westerly known colony in England.

This is not the end of the story however. Earlier this summer, volunteer recorders caught several Olive Crescent in the east of Hampshire and western West Sussex. Almost all of the captures were made in suitable breeding habitat, rather than along the coast so they suggested that the moth might be breeding in the area.

So this week, between the torrential downpours, BC staff have looked for larvae in woods near Petersfield in Hampshire and Graffham in West Sussex and have been successful at both sites. It seems likely that the moth is now resident in large beech and oak woods from the Kent borders right across to east Hampshire and perhaps the title of this blog should be ‘Formerly rare moth on the move’.  

Tony Davis
Moth Conservation Officer