Flea beetles are small, dark beetles that jump like fleas when disturbed. Adults chew numerous small, round holes into leaves (most damaging to young plants), and larvae feed on plant roots. Spray plants with garlic spray.

Alder leaf beetle is an 7-8 mm long dark metallic blue beetle that feeds on alder and is occasionally found on other deciduous trees such as beech, hazel and hornbeam. It overwinters as adults which emerge in the spring, sometimes in large numbers.

The black caterpillar like larvae produced also feed on the leaves of alder and other trees and reach 11 mm in length. Larvae can be found on the leaves from May to July .Pesticides are likely to be more effective against larvae than adults.