What is oak processionary moth?
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.