Principle species colonised.

The most critical clue is the host. OPM lives and feeds almost exclusively on oak trees. If you see caterpillars or nests on other tree species (like blackthorn, hawthorn, or fruit trees), they are likely a different, often harmless, species like the Lackey or Ermine moth.

Identification.

April through July is when caterpillars are most active. They travel in lengthy, nose-to-tail lines, as their name implies (processions). These frequently take the appearance of an arrowhead and might be single-file or many caterpillars wide.

They are coloured with a dark head and a grey body. Older larvae have whiter stripes on either side of a noticeable dark stripe in the centre. They have long, white hair all over them.

Type of symptoms.

The plaques are typically found on bark fissures, but they can also be found on walls, fences, or any other rough, protected surface in urban settings.

The threat to host.

OPM caterpillars consume the leaves of certain oak tree species, OPM is considered a tree pest. Whole oak trees can be stripped naked by large populations, making them more susceptible to diseases, pests, and other pressures like drought.

Impact / Effect / Significance

The species gets part of its scientific name from the microscopic hairs that older caterpillars produce that carry an unpleasant protein called thaumetopoein. Both humans and animals who come into contact with the hairs may get sore throats, breathing problems, eye irritations, and itchy skin rashes like the one shown above. May and June are the months with the biggest danger of being exposed to these hairs.

When the caterpillars feel frightened or disturbed, they may shed their hair. The caterpillars’ nests may tumble to the ground after the hairs are carried there by the wind. They can adhere to clothing, trunks, branches, grass, and tools like ropes used by forestry and ground care personnel as well as tree surgeons.