Warning over oak processionary moth nest in Carpenders Park

Hertfordshire County Council has confirmed that a tree in Compton Place currently has a caterpillar nest from the oak processionary moth breed (OPM).

The caterpillars and their nests are deemed a “hazard to human and animal health” by the Forestry Commission as their hairs can cause rashes, eye and throat irritations, breathing difficulties and even an allergic reaction in rare cases.

HCC has confirmed the nest in Compton Place was made by hazardous OPM caterpillars. (Image: Geetha Bala) A spokesperson for the county council said it had instructed a specialist contractor to remove the nest and caterpillars on the highway tree next week, and that the affected area will be sprayed to prevent a short-term re-infestation.

They added: “Whilst the tree is unaffected the caterpillars and silk nests do present a public health concern, so we’d like to remind the public not to approach or touch the caterpillars or nest.”

OPM caterpillars usually appear on oak trees from late March to May and can be recognised by their black heads and grey bodies covered in long white hairs.

They retreat into their nests from late June to early August before re-emerging as adult moths.

Guidance from the Forestry Commission says the greatest risk to people and animal’s health is between May to July when the caterpillars are active.

It recommends residents keep their distance from infested trees as hairs can be caught on clothing while moving past or blown off the nests into the air.

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Anyone who has a serious allergic reaction from contact with the moths is urged to seek medical help, while more minor reactions can be dealt with by a pharmacist.

Residents are urged to report OPM nests to the Forestry Commission through the Tree Alert online form and inform their neighbours with oak trees.

The breed were first identified in London in 2006 and have spread to surrounding counties including parts of Hertfordshire.

An interactive map from the Forestry Commission shows there have been multiple sightings in the Watford area in recent years, including two in South Oxhey and Carpenders Park in 2023.