A deadly species of caterpillar has been spotted in Watford.

The creatures, who go by the scientific name of oak processionary moths, are said to be highly toxic and can cause severe asthma attacks and skin rashes on humans.

Hertfordshire County Council confirmed sightings at a site near Watford Junction station (below) and said it was "inevitable" the pest will spread through the county.

The caterpillars cause significant damage to oak trees by consuming their foliage and can also pose a health risk to people and animals.

People are strongly advised not to touch the caterpillars or interfere with their nests as their microscopic hairs contain a toxin that is known to cause itchy skin rashes, itchy eyes and a sore throat.

The oak processionary moth caterpillar gets its name from the creatures' habit of forming long lines in trees.

Each caterpillar has around 60,000 hairs which can be carried in the wind.

Jim McManus, director of public health for Hertfordshire, said: "The key risk to pets and humans is the hairs from the caterpillars, which can cause very severe irritation.

"We strongly support the 'don't touch' advice from the Forestry Commission, and advise people not to approach the caterpillars or their nests.

“People should also keep their pets and livestock away as well. If you have asthma or allergies or have been prescribed an epipen, you should carry these with you when outdoors.

“We have issued advice to local GPs and health professionals and to accident and emergency departments to help them identify when patients have been affected by the caterpillars, and to advise them on treatment.

"See a pharmacist for relief from milder skin or eye irritations following possible OPM contact, or consult a GP or NHS111 for more-serious reactions. If you develop serious breathing difficulties contact 999. Contact a vet if animals are seriously affected."

The oak processionary moth caterpillar;

The creatures were first identified in Britain in 2006 in west London and are thought to have been transported on trees from Europe used for a landscaping project.

In 2007, the situation got so bad in Belgium that the army was called in to incinerate the nests.