Oak Processionary Caterpillars and Dogs
The hairs from oak processionary moth caterpillars and their nests can cause serious irritation in people and animals.
What is the oak processionary moth?
The oak processionary moth is a pest whose caterpillars feed primarily on oak trees. The caterpillars are named after their habit of moving together in nose-to-tail processions.
They have dark heads and greyish bodies covered with long white hairs. Their silken nests are normally found on the trunks or branches of oak trees. Fresh nests may appear white but become brown and discoloured with age.
Why are they dangerous?
From their third growth stage onwards, the caterpillars develop thousands of tiny, barbed hairs containing an irritating substance called thaumetopoein.
Contact with the hairs can cause itching, skin rashes, eye and throat irritation and, occasionally, breathing difficulties. Rarely, a more serious allergic reaction may occur.
The hairs can be present on the caterpillars, in their nests and on nearby bark or grass. They may also be carried through the air by the wind. The greatest risk is normally between May and July, but old nests can remain hazardous throughout the year.
Risk to dogs and other animals
Dogs may sniff, lick or pick up a caterpillar or nest. They can also collect the hairs on their paws or coat and then transfer them to their mouth while licking themselves.
Possible signs following exposure include:
- Sudden swelling of the face, lips or tongue
- Redness, irritation or blistering inside the mouth
- Drooling or repeated swallowing
- Pawing at the mouth or face
- Vomiting or retching
- Swollen or irritated eyes
- Skin irritation or intense itching
- Difficulty breathing
- Weakness or collapse
What should you do?
- Move your dog away from the area immediately.
- Do not touch the caterpillar, nest or contaminated area.
- Prevent your dog from licking its paws or coat.
- Telephone your vet and explain that exposure to oak processionary caterpillar hairs is suspected.
- Follow your vet’s instructions and take the dog for treatment promptly if advised.
- Do not give medication unless instructed by a veterinary surgeon.
How to protect your dog
- Keep dogs on a lead near oak trees in affected areas.
- Do not allow dogs to sniff or investigate caterpillars or nests.
- Avoid spending time beneath or downwind of infested trees, particularly on windy days.
- Keep dogs away from fallen nests and contaminated grass.
- Never attempt to remove or destroy a nest yourself.
An owner’s experience
An owner described how two of her dogs became seriously ill during a weekend away. One dog developed swollen eyes, ears and face, lumps over the body and difficulty breathing. The second dog became extremely hot, weak and collapsed, with swollen feet and breathing difficulties.
Both dogs were taken immediately to a 24-hour veterinary practice, where they received emergency treatment, intravenous fluids and close monitoring.
Friends searching the area found a caterpillar close to the dogs’ beds. After speaking to an animal poison information service, the vet considered that contact with caterpillar hairs could explain the dogs’ symptoms. It was possible that the dogs had picked up or mouthed the caterpillar.
Both dogs remained at the veterinary practice overnight and were well enough to return home the following day. Their rapid recovery demonstrates how important it is to obtain immediate veterinary attention when a severe reaction is suspected.
Reporting a sighting
Suspected sightings of oak processionary moth caterpillars or nests can be reported through the Forestry Research TreeAlert service. If the tree is on council property, you can also notify the relevant local authority.
Do not approach the nest to obtain a closer photograph and do not attempt to remove it yourself. Specialist pest-control operators should carry out any necessary removal.
Sources and further information
This page provides general information only and is not a substitute for examination, diagnosis or treatment by a qualified veterinary surgeon.