Join the RHS today and support our charitable work
Free personalised gardening advice
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Free entry to RHS members at selected times »
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Help us achieve our goals
Join the RHS today and support our charity
I have forgotten my password
Register for free to receive our newsletters, add comments to blogs/articles and to save content.
See what events are on near you and browse your bookmarked pages.
Oak processionary moth is a non-native moth that has become established in parts of London and its surrounds. Whilst it can defoliate oak trees the primary concern is the caterpillars hairs, these can cause irritation if in contact with human skin. These caterpillars should not be handled nor approached .
Oak processionary moth caterpillars © Forestry Commission
Oak processionary moth has caterpillars that are covered in irritant (urticating) hairs that can pose a health risk to humans and animals. The moth is not native to the UK but has become established in London and some surrounding areas since it was first found in south west London in 2005.
Adults moths are brown with a wingspan of 25-35mm and are similar in appearance to several other moth species found in the UK. They emerge from pupae in mid to late summer and only live for a few days in which time they mate and lay eggs usually high up in oak trees. The moth overwinters as eggs. The eggs hatch in spring, between March and late April. The caterpillars usually initially feed high up in oak trees, and at this stage often go unnoticed.
By late spring to early summer the caterpillars become larger (20-25 mm) and are dark in colour covered with many white hairs. At this stage they become easily recognised as they have the distinctive habit of moving around in nose to tail processions, which give the species its name. The caterpillars also construct white webbing nests on trucks and branches of oak trees. At this time the caterpillars spend much of the day in the nests leaving in processions to feed at dawn and dusk.
When the nests and processions of caterpillars become visible it is at this stage that the irritant (urticating) hairs have developed which pose the potential of causing rashes and respiratory problems in humans and animals.
Whilst the caterpillars can defoliate parts of oak trees the most obvious signs of the presence of this moth are the dark hairy 25mm long caterpillars which are present in late spring and early summer. They are easily recognised as they have moving around in nose to tail processions, these processions usually leaving white silken trails behind.
In addition the caterpillars construct white webbing nests on trucks and branches of oak trees. The white silk often discolours brown. During late spring and early summer the caterpillars spend much of the day in the nests leaving in processions to feed at dawn and dusk, occasionally they will process between oak trees. The empty nests can remain present throughout the winter.
The caterpillars of oak processionary moth can defoliate oak trees however it is the irritant (urticating) hairs that have the potential to cause health problems to humans and animals. For medical advice see NHS choices.
The moth is native to southern Europe but has recently become more widespread in northern Europe. It appeared in South West London in 2005 and has since become widespread in West and South West London. There have also been outbreaks in East London, Hertfordshire, Berkshire and parts of Surrey.
It is the subject of a control and containment programme co-ordinated by the Forestry Commission.
Before reporting an infestation please check the information on the Commission's website. Key identification points;
If you are still convinced they are indeed oak processionary moth caterpillars, what should you do?
Angle shades moth
Box tree caterpillar
Brown tail moth
Buff tip moth
Cotoneaster webber caterpillars
Elephant hawk moth
Encouraging moths in your garden
Forestry Commission information on oak processionary moth
Holm oak leaf-mining moths
NHS information on UK bugs that bite or sting
Oak gall wasps
Small ermine moths
Swift moth caterpillars
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.