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Oak processionary moth is a moth native to southern Europe 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 Britain but has become established in London and some surrounding areas since it was first found in south west London in 2005. If the caterpillars are found outside of the London and Surrey outbreak zones it should be reported via TreeAlert
Adults moths are brown with a wingspan of 25-35mm and are similar in appearance to several other moth species found in Britain. 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. Caterpillars were also found on recently imported trees in Cardiff, Hampshire and Birmingham in 2019. There are now tough restrictions on importing oaks into the UK reducing the risk of the caterpillars being imported, find out more here
It is the subject of a control and containment programme co-ordinated by the Forestry Commission.
Before reporting a suspected case of oak processionary moth 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?
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