A species of gall forming wasp, new to the UK, has been found in a few private gardens in the southeast of England and the same species, or similar closely related species, has been found at a plant nursery in Yorkshire. The identity of the organism has not been confirmed but it is very similar to Ophelimus maskelli an Australian species and pest of Eucalyptus that has established in Israel and in southern EU Member States, e.g. France, Greece, Italy and Spain. Very high densities of galls can occur on young leaves. Severe damage can result and mature trees can loose almost all leaves. Ophelimus maskelli is most likely to establish more widely in southern Europe where Eucalyptus hosts occur widely as forestry and amenity trees. Damage is to be expected. The climate of the UK is probably less suitable and it is likely that populations in the UK will be smaller, hence less damaging. No chemical control measures are described in the literature. A hymenopteran parasitoid biological control agent has shown some success at controlling this pest in Israel.