England
The caterpillars were accidentally introduced to the UK in 2005, almost certainly as eggs on live oak plants imported from continental Europe. Later distribution of the pest probably arose from several similar introductions, in addition to spread from the original point of introduction.[1] By 2019 they had spread to all 33 London boroughs, and the Government had spent £37 million trying to control them.[7] The general public have been asked to look out for these caterpillars and to report them, rather than deal with them themselves. The London Boroughs of Brent, Ealing, Hounslow and Richmond upon Thames set up task forces to deal with outbreaks. Sightings of these caterpillars in other areas should be reported to the Forestry Commission,[8] whose research agency issued guidance on the way to contain outbreaks and deal with infestations, so as not to increase the risk to the public.[9]
On 31 March 2008 an emergency amendment added the moth to the list of pests in The Plant Health (Forestry) Order 2005, and has required all oak trees coming into the UK from the rest of Europe to have Plant Passports.[10]
In 2013 the Forestry Commission announced helicopters would be deployed to "blanket spray woodland" where the caterpillars posed a health threat.[3]
In April 2018 an outbreak of the caterpillars was reported across Greater London and surrounding areas.[11] In 2015 fifteen OPM nests were found in Hampstead Heath, Highgate Wood and Queen's Park; in 2018 over 2,000 were found at those sites

Belgium
The moth is reported as being fairly common in Belgium, notably in the Campine but also elsewhere, the population fluctuating from year to year.[12] In 2007 infestations in the province of Limburg were so acute that soldiers were deployed to burn them.