Health & Safety Tree Survey

Oak Processionary Moth


PestS on Trees

Oak Processionary Moth (OPM)

It may only recently have been making headlines but Oak Processionary Moth, or OPM as it is more commonly known, has been in the UK for around 10-13 years. It was transported here from the European Continent on tree stock, which was planted in Richmond. It was thought that the M25 may contain the infestation but unfortunately an increasing number of infestations are now being found outside of this area.

But what does it actually do?

The moth itself was originally thought to be able to fly about 1 mile per year, this has now been updated to approximately 3-5 miles per year, meaning a faster spread of the moth.

The problem for humans and animals (as well as Oak trees), and why they are of such concern, stems from the Caterpillar rather than the moth. The caterpillars start out as larvae when the migrated moths lay their eggs in small nests in September. The caterpillars are visible to the public from the week beginning 14th of May, this is mostly down to the caterpillars developing white hairs (called setae) all over their bodies and it is these hairs that are the problem to humans and animals. OPM setae contain a toxin that is poisonous to both humans and animals if they are ingested or come into contact with skin. They cause serious respiratory problems and inflammation of the skin. We compare it to spending 2 weeks out in the Caribbean sun without sun cream - NOT NICE! 

So what do we do if we're worried about this?

Well, the more important matter is what not to do.


  • touch or approach nests or caterpillars;

  • let children touch or approach nests or caterpillars;

  • let animals touch or approach nests or caterpillars;

  • try removing nests or caterpillars yourself.


Contact SMW (Tree) Consultancy ltd for advice. Usually we will need to carry out a tree survey to ascertain the extent to which your Oak tree is infected and if so, what to do next.