UK public issued 'do not touch' warning over toxic insect that emerges in summer

Oak processionary moth caterpillars are usually found in clusters and move in nose-to-tail processions
-Credit: (Image: Forestry Commission)

A health warning has been issued to the UK public over an invasive insect that "should not be touched under any circumstances" due to its toxic nature.

Oak processionary moth caterpillars are named as such because they nest almost exclusively on oak trees, and can typically be seen crawling around branches in a cluster or procession. The hairs on these caterpillars, which are also found in their white silken webbing and nests, contain a toxic substance that can cause itchy rashes, eye and throat irritation, and sometimes breathing difficulties in both humans and pets.

With the greatest risk period for the species being from June to August, the Forestry Commission has urged the public to report any sightings of oak processionary moth caterpillars, as in addition to posing a health risk to people they can cause significant damage to oak trees. The caterpillars feed on the tree's leaves as they migrate which harms their growth and weakens the tree, leaving it vulnerable to other stresses such as drought and disease, the experts explained

The caterpillars are native to southern Europe, but have now become established in parts of England after having been accidentally transported over to UK shores in trees for planting. The insect was first identified in London in 2006, and has since spread to surrounding counties in the South East despite ongoing efforts to eradicate it.

Although oak processionary moth caterpillars have so far not been detected further north than Milton Keynes, they are becoming more common as rising temperatures help them to spread to new areas, so it's worth being aware of their appearance regardless of where you live in the UK. However, the public are urged never to try and dispose of the nests, found in the trunk or branches of oak trees, themselves, and to instead report any sightings "immediately" via the TreeAlert website.

Andrew Hoppit, oak processionary moth project manager, said: "It is important those living and working in areas affected by oak processionary moth remain vigilant about the health risks they pose, when enjoying outdoor spaces, as we are entering the greatest risk period."

Professor Nicola Spence, UK chief plant health officer, added: "Oak trees are an iconic and much-loved part of our British landscape. By reporting any sightings of the oak processionary moth to the Forestry Commission, we can all minimise the pest's spread as well as reduce their impact on tree health."

Here's a list of criteria from the Forestry Commission on how to identify an oak processionary moth caterpillar:

  • They live almost exclusively in oak trees, which are identifiable by their distinctive leaves

  • They move in nose-to-tail processions, in oak trees or on the ground, hence their name

  • They often cluster together

  • They build white, silken webbing trails and nests - usually dome or teardrop-shaped - on oak trunks and branches (not among the leaves)

  • They are found predominantly in the south of England - you can see a distribution map of confirmed sightings here.