Moths on Oaks - Oak Processionary and Green Oak Tortrix

For many years we have been advising you to be careful around Oak trees, particularly when the caterpillars of the Oak Processionary Moth (OPM) start to appear in May/June. We are really pleased that the message is getting out there and many of you do call us to to let us know when they find a nest that we might have missed - on a site this size, your eyes and ears on the ground are a really big help to our staff.

Aside from OPM, there are several species of moth that favour the Oak trees and one of them, the Green Oak Tortix - is also now emerging.  You will recognise the larvae as the small green caterpillars that always seem to hang at head height during April/May and tangle themselves in your hair!

Please be assured that the Green Oak Tortrix moths are harmless.  They are a very common moth in many parts of Britain and although the larvae can become a pest, they generally do not become a problem for our Oak trees here on the Commons. However, this year seems to be a bumper year and the sound of the caterpillars munching on the young ouak leaves is quite noticeable.  The Oak trees are well able to deal with this and, even if denuded of the fiorst flush of leaves, they will produce what's know as "Lammas leaves", a second flush of growth during July and August and will make a full recovery. 


A few Oak Processionary Moth facts: 

Whilst we're talking about Oak Processionary Moth, there has been a lot of press about them over reacent years, some of it slightly sensational, with headlines such as "Toxic caterpillar outbreak across southern England" and "An outbreak of toxic caterpillars have descended on London".

Here are a few facts to clear that up:  

  • OPM arrived in London at least 10 years ago, so it's been here a while and hasn't just "landed".
  • It is not toxic, that would indicate it is poisonous which it isn't. What it has are urticating hairs which are an irritant, but they won't poison you.
  • Do you still need to take care?  Yes.  You, your children and your pets should be careful around oak trees as the hairs of the caterpillars can cause irritation if touched or inhaled. The caterpillars started to appear in mid-April and will be present until they pupate into moths around July time. 
  • You will not usually see the moths as they will generally only fly at night and, if you do, they are not dangerous.
  • The hairs and pupae cases that the caterpillars leave behind can still be irritating so if you do see any that you believe are a hazard to the public, please call us and let us know.  Do not try to remove them yourself.

If you have any concerns or queries about any wildlife you see on the Commons, do call us on 020 8788 7655