Oak processionary caterpillars are now beginning to emerge from nests in oak trees ahead of their transformation into moths.

The caterpillars are each covered in tiny hairs that can cause itchy and painful rashes if they come into contact with skin. They can also cause irritation to eyes and throats.

The hairs can be blown on the wind and left in the silken, web-like nests that the caterpillars build in oak trees.

The spread of this pest is causing tree experts and public health officials some concern. In 2007, the Forestry Commission collected and destroyed 708 nests. That figure rose to 4,410 in 2011.

The Forestry Commission and public health authorities are now raising awareness of the issue in a bid to contain the pest and halt its spread.

Alison Field from the Forestry Commission urged the public to report infestations - but to steer clear of touching the caterpillars or their nests.

She said:
"We welcome reports of caterpillars or their nests from the public or others, such as gardeners and tree surgeons, who are out and about in areas with oak trees.  However, the public should not try to remove the caterpillars or nests themselves. This task needs to be carefully timed to be most effective and is best done by specially trained and equipped operators."

Dr Brian McCloskey from the Health Protection Agency added:
"Anyone who experiences an itchy or painful skin rash or a sore throat and irritated eyes after being near oak trees should consult their GP or NHS Direct.  We have issued advice to local GPs and other health professionals to help them identify when patients have been affected by the caterpillars and to advise them on appropriate treatment."

Anyone who spots a nest or thinks an oak tree is infested with these caterpillars should contact the Forestry Commission on 0131 314 6414. For further information visit the commission's website.