Are There Any Dangerous Caterpillars In The UK?

The Government has issued a warning on oak processionary moth caterpillars “ahead of peak season”.

They have said it’s important for the public to “stay vigilant” as the “pest” begins to make its hairy way onto oak trees.

Not only can they harm the iconic trees, which The Tree Council has described as being “under threat” in the UK, but they can also cause irritation “and should not be touched under any circumstances”, the Government said.

They’re the caterpillar, or the younger stage, of the oak processionary moth.

The Forestry Commission’s Oak Processionary Moth Programme Manager, Dr Edward Straw, said we might see more of these than usual as “The warm weather in spring has led to oak processionary moth growing quicker than in previous years and we may see higher infestation levels”.

They’re about 2-3cm-long caterpillars with a grey body and a dark head with lengthy, white hairs. They usually form a nose-to-tail formation in groups as they travel down oak trees.

They have nests which the Government has said are usually teardrop-shaped or dome-shaped and can range from the size of a 50p coin to that of a melon. These look white at first, but can turn brown later on.

Forest Research said that while the invasive oak processionary caterpillar looks like harmless native species – including the lackey moth and brown tail moth caterpillars – there are ways to distinguish the “pest” from the rest.

They said, ”(The) oak processionary moth feeds only on oak and produces large nests on oak trunks and large branches from May onwards. Hairy caterpillars which are not on oak or are not associated with a silk nest are almost certainly not (oak processionary moths)”.

They’re usually found in the South-West of the UK.

Professor Nicola Spence, Defra Chief Plant Health Officer, said: “I would advise that members of the public living in the South East, Derbyshire and Dorset, avoid any contact with the caterpillar and its nests, as this can cause irritation”.

Firstly, they feed on the leaves of oak trees, which means they can hamper the trees’ growth. This can leave them more vulnerable to disease.

Secondly, the tiny hairs on the caterpillars’ bodies can “cause itchy rashes, eye and throat irritation and should not be touched under any circumstances,” said the Government.

Firstly, don’t touch them. Don’t even touch the nest, the government warned, as this could contain the irritating hairs.

Secondly, report any sightings so experts can keep track of the caterpillars.

“If you spot the pest, report the sighting via our TreeAlert portal. Alternatively, you can email opm@forestrycommission.gov.uk,” Dr Straw said.

The Royal Horticultural Society (RHS) also said that “Due to the irritant hairs, control of this insect should only be carried out by professional contractors”.

The government previously said, “if you or someone in your care has a serious allergic reaction, get medical help. For less severe reactions, a pharmacist can provide advice on relief from skin or eye irritations.”

They also say that “if an animal in your care is seriously affected, get advice from a vet”, and warn to “Tell the medical person or vet you suspect it is due to OPM [oak processionary moth] contact.“