Please take care as Oak Processionary Moth Caterpillars have been found on Hampstead Heath. They can affect the health of both humans and animals.
The oak processionary (Thaumetopoea processionea) is a moth whose caterpillars can be found in oak forests, where they feed on oak leaves, causing significant damage. They travel in nose-to-tail processions (hence their name), often arrow-headed, with a leader followed by rows of several caterpillars abreast. They are a human irritant because of their venomous setae (hairs), which can cause skin irritation and asthma.
The wiki page here has all you ever wish to know about them.
Its great that The City of London have posters about this on the Heath - and what to do if you find them!
