Alder leaf beetles

 Low Barns is Durham Wildlife Trust’s largest wetland reserve and the commonest trees there are alders, whose leaves are currently being consumed by a population explosion of these jewel-like, metallic-blue alder leaf beetles Agelastica alni.

Until quite recently, the alder leaf beetle was considered to be a rare species, in danger of extinction in Britain. Then, in 2004 it reappeared in north-west England and over the last twenty years it has become increasingly common in the north east. No one has really identified the reason for its success but it’s common in France, so perhaps it arrived with imported plants from continental Europe. The adult beetle and its larva partially defoliate alders but they recover every spring. The adult beetles fall with the alder foliage in autumn and survive winter in the leaf litter.