Oak processionary caterpillars: the risks and what to do

Keep your distance, including from an old, empty nest.

The answer in 2 lines. In England, the established concern is oak processionary moth, especially in parts of the south east. Its caterpillars and nests contain irritating hairs that can cause rashes, eye or throat irritation and breathing problems. Keep children and animals away and report suspected sightings through the official reporting service. Do not remove nests yourself. Pine processionary moth has no known established UK populations according to the official guidance checked for this guide; report suspicious findings rather than assuming an identification.

What to do first

Move away from suspected caterpillars, nests and the affected tree. Keep children away and dogs on a lead.
Observe from a distance. Note the location and take a photograph only if you can do so without approaching.
Report suspected oak processionary caterpillars or nests through TreeAlert: provide the location, describe what you saw and attach a safe photograph if available.
If the tree is yours, follow the official management guidance before arranging specialist treatment or removal.

Stop: danger

Severe allergic reaction: call 999 for sudden swelling of the mouth, tongue or throat, difficulty breathing, collapse or inability to wake someone. The NHS symptoms guide explains the emergency warning signs.
Eye symptoms or worsening illness: avoid rubbing your eyes and seek medical advice. Call 111 for urgent advice when it is not a life-threatening emergency, and explain the suspected exposure.
Affected pet: contact a vet urgently for mouth swelling, excessive drooling, breathing difficulty or distress after possible contact. Tell them you suspect oak processionary hairs; do not delay for a home remedy.

Recognise the signs without getting closer

Oak processionary caterpillars have dark heads, grey bodies and long white hairs. They commonly move nose-to-tail and live mainly on oak trees. Silken nests attach to trunks or branches and darken as they age.

Use the identification photographs in the Forestry Commission’s England guidance to compare a sighting from a safe position. Other caterpillars are often mistaken for this species: the Forest Research comparison page helps distinguish them. A line of caterpillars or a web alone does not confirm identification.

After hairs contact your skin

Follow the NHS instructions under ‘How to remove caterpillar hairs’: rinse with running water, allow the skin to air dry and use sticky tape to lift remaining hairs from skin. Remove jewellery in case of swelling, change clothing and wash affected clothes at a high temperature.

Do not scratch or rub the area. Ask a pharmacist about symptom relief and explain that caterpillar hairs are involved: the NHS advises against antihistamine cream after this exposure. Seek further advice if symptoms worsen or do not improve. Skin first-aid instructions should not be used inside the eyes or mouth.

What not to do

Picking up caterpillars, fallen nests or apparently abandoned nest material.
Cutting, burning, sweeping or pressure-washing a nest yourself.
Mowing or disturbing material beneath an affected tree before the risk has been assessed.
Allowing children to investigate a procession or pets to sniff and lick it.

Reporting, removal and who pays

For a public tree, tell the site manager as well as submitting the sighting. Include a clear location so they can identify the tree without asking you to approach it. A report does not itself confirm the species or guarantee immediate removal.

For your own tree, use the official England management guidance: open its management-zone information, locate your site and read the instructions for that area. Responsibilities and government support depend on the zone; do not assume either that treatment is free or that every owner must arrange the same action.

Removal is hazardous and should be assessed by a specialist experienced in this pest. Ask how people and animals will be kept away, how contaminated material will be handled and what follow-up is needed. Retain the report and any official notice.

What about pine processionary caterpillars?

The Forest Research pine processionary page states that no established UK populations are known. It explains the signs and gives reporting contacts under ‘Report a sighting’. If you suspect this species, use the England contact there and supply the location and safe photographs. Do not move the caterpillars, nest or affected plant to obtain an identification.

Good to know

The Forestry Commission identifies May to July as the greatest-risk period, but hairs in old nests can remain hazardous at other times.
Hairs can be carried by wind. Lack of direct contact does not rule out exposure.
The Forest Research health manual explains animal exposure; use its prevention advice to plan access around affected trees.
This guide covers England. For Wales, Scotland or Northern Ireland, follow the national links in the official management guidance.

Illustrative example: a dog walker in Surrey notices a silken patch on an oak trunk. She keeps her dog away, records the tree’s location and submits a distant photograph through the reporting service. She tells the park manager and chooses another route while the sighting is assessed.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 6 November 2026, for England. Confidence: high for health precautions, reporting and the distinction between oak and pine processionary moth; medium for identification without expert assessment and for treatment funding, which depends on location and official instructions. The England management guidance was updated in 2026.