Sightings of a hairy caterpillar, that can make humans and pets very unwell must be reported this summer - but people are being urged not to touch them.

England is about to enter its ‘greatest risk period’ when oak processionary moth caterpillars emerge before turning into adult moths.

Their appearance - usually between mid May and July - can pose a risk to the public and their animals because the creatures and their nests contain long hairs that can cause itchy rashes, eye and throat problems and sometimes breathing difficulties.

The caterpillars - say officials and wildlife charities - should not really be touched under any circumstances.

Oak processionary moths are officially classified as tree pests having been first identified in London back in 2006.

Since then the creature has spread in much larger numbers - and outside the capital - to many surrounding counties paricularly in the south east of England.

Alongside their ability to make people and pets feel unwell, the caterpillars have been classified as a pest because of the potential damage they can cause to oak trees.

Their desire to feed on several species causes the trees to lose their leaves, can affect their growth and ultimately lead to them becoming more vulnerable to other stresses like drought.

A Forestry Commission spokesperson said: “As we are now entering the season when the oak processionary moth caterpillar is most visible, it is important that people living in areas affected by the caterpillars and their nests, including Kent and Surrey, are vigilant when out and about, and avoid touching them.

“To safeguard tree and human health, it is important that members of the public report any suspected sightings.”

How to identify an oak processionary moth caterpillar

The caterpillar nests are typically dome or teardrop-shaped and usually around the size of a tennis ball.

The caterpillars, which are about 2cm long when fully grown, will have black heads and bodies which are covered in long white hairs.

It is a protein in the hair which will cause itchy rashes, eye, and throat irritations.

Speaking last year about the potential spread of the caterpillars the UK’s chief plant health officer, Professor Nicola Spence, explained: "Our oak trees are an iconic part of our British landscape. Reporting any sightings of oak processionary moth to the Forestry Commission will both minimise the pest’s spread and reduce the damaging impact it poses to tree health.”

Reporting sightings

Anyone who spots this particular caterpillar in the weeks ahead is asked to report their sighting to the Forrestry Commission.

This can be done via the Commission’s Tree Alert portal here. Alternatively call 0300 067 4442.

Sightings can also be reported by emailing opm@forestrycommission.gov.uk.

Anyone who thinks they have come into contact with one of the caterpillars should visit a pharmacist for help with milder reactions or consult a GP for more serious reactions.

If animals have been seriously affected animal owners should contact their vet for help and treatment.