People are being urged to watch out for a dangerous insect during the warm weather.

As the warm weather continues, sunseekers enjoying the outdoors have been asked to keep an eye out for the tree pest Oak Processionary Moth (OPM) caterpillars.

Hertsmere Borough Council says the OPM has been spotted in Meadow Park, Borehamwood, private woodland in Ridge, Bushey Hall Golf Club, and Parkfield in Potters Bar.

The creatures contain hairs which can cause itchy rashes and eye and throat irritations. They should avoid being touched in all circumstances.

They can be identified by their nests that are typically dome or teardrop-shaped, averaging the size of a tennis ball.

The creatures are white when fresh, but soon become discoloured and brown.

They feed on oak leaves and can increase trees’ vulnerability to attack by other pests and diseases, making them less able to withstand adverse weather conditions such as drought and floods.

The greatest risk period is May to July, when the caterpillars emerge and feed before pupating into adult moths.

Council officers have found infestations on a few council sites across the borough.

A survey is ongoing in locations in Hertsmere heavily used by the public to establish the current spread and find a strategy to remove existing infestations.

Councillor Seamus Quilty, responsible for the environment at the council, says this will not involve the loss of any infected oak trees.

Cllr Quilty added: "Unfortunately, Oak Processionary Moths have been sighted in a few Hertsmere parks, so our message is to be vigilant, especially with young children who may be exploring trees this summer.

"Our parks team is working to control the spread of the Oak Processionary Moth and will be putting up safety notices in those parks affected to warn the public. If you discover an OPM nest or caterpillar, we ask that you 'spot it, avoid it, report it'."

If you see any oak processionary nests or caterpillars (OPM) in a council park you should report them immediately on 020 8207 2277 or email

If they are on a privately owned oak tree, report them to the Forestry Commission by calling 030 0067 442 or emailing