Oak Processionary Moth Nest Or Rash

What's happening?

GOV.UK says oak processionary moth caterpillars infest oak trees, eat the leaves and weaken the tree, and that the nests and caterpillars are a hazard to human and animal health. The caterpillars have black heads and grey bodies covered in long white hairs, and when they reach 1cm long they develop irritating hairs. Nests are usually found in early summer in the trunks and branches of oak trees, are typically dome or teardrop-shaped, white when fresh and soon discoloured and brown. You are unlikely to find them on other trees, fences or walls. The RHS says the caterpillars move in nose-to-tail processions and should not be handled or approached. GOV.UK says the greatest risk is between May and July, but old nests leave residual hairs.

What usually causes it?

• Caterpillars on an oak tree, usually in a procession up the trunk or on the branches
• A white or brown dome or teardrop-shaped silk nest on an oak trunk or branch
• Irritating hairs blown by the wind from infested trees nearby
• Residual hairs from old nests, which GOV.UK says can pose a risk at any time of year
• A harmless caterpillar mistaken for the pest, which GOV.UK says is often reported

Is it dangerous?

Medium. GOV.UK says the hairs can cause itchy rashes, eye and throat irritations and occasionally breathing difficulties in people and animals, and that you can become sensitised by repeated exposure. It says not to touch or get close to caterpillars or nests. If you or someone in your care has a serious allergic reaction, get medical help. For less severe reactions a pharmacist can advise on relief from skin or eye irritations.

Can I fix it myself?

Do not touch, remove or try to dispose of caterpillars or nests: GOV.UK says removal is hazardous and recommends a professional, and you can find an OPM management professional through the Arboricultural Association. Keep children and pets away. Check the GOV.UK guide to species commonly confused with oak processionary moth before reporting. Report a nest or caterpillars through TreeAlert, as GOV.UK says, with what its OPM resource hub asks you to include.

When should you call a tree surgeon?

Call a professional OPM management contractor for removal, through the Arboricultural Association's list. If you own or manage the oak, report it through TreeAlert first, because GOV.UK says you must report it immediately, and says a Statutory Plant Health Notice may be issued asking you to take action.

What will the tree surgeon actually do?

• Identify the caterpillars or nests and distinguish them from harmless species
• Remove nests and caterpillars safely with the right protective equipment
• Report the findings through TreeAlert where required
• Advise on residual hairs and on keeping people and animals away
• Carry out any action required by a Statutory Plant Health Notice

Questions people ask

Sources & References

1. GOV.UK: managing oak processionary moth in England
2. RHS: oak processionary moth, safety and control