As you will probably know, there are a lot of oak trees on the Heath and these could be affected by the oak processionary moth (OPM) following an outbreak in Watford.
OPM can affect trees, people and animals, and was first discovered in England in London in 2005. Tree and public health authorities in Hertfordshire have been preparing for the possibility of its spreading into the county.
The caterpillars shed thousands of their tiny hairs in the nests, and these can cause itchy skin rashes and eye irritations. In extremely rare cases, they can cause breathing difficulties in people and animals. The caterpillars eat oak leaves, leaving infested trees weakened and vulnerable to other threats.