In 2009, Natural History Museum, London, lepidopterist David
Lees joined a project to study horse chestnut leaf miner moths
(Cameraria ohridella), which are currently infesting trees
across much of Europe, defacing their leaves with distinctive
brown scars. Researchers first discovered the insects in 1984
infesting trees in Macedonia, but they weren’t sure where the
insects had come from or what might be done to stop them.
Entomologists started tracking the leaf miner’s spread in 1989,
when the moths suddenly began racing across Europe at the
breakneck speed of 60 kilometers per year, finally turning up in
Britain in 2002. “Now it’s everywhere,” Lees says. The insect’s
host, the horse chestnut tree, is prized by landscapers for its
beauty and in the Balkans its fruits were traditionally fed to
horses to treat cough. And its nuts, called conkers, are game
pieces in the annual World Conker Championships held every
autumn in Northamptonshire, England. Players swing a nut
attached to a string at an opponent’s con