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Oak Processionary Moth

Thaumetopoea processionea

Oak Processionary Moth, Cluster Caterpillars, Oak Processionary Caterpillar

A close up of a Thaumetopoea processionea Oak processionary moth mating pair

Thaumetopoea processionea male & female Saarland 004

by Orchi. CC-BY-SA-3.0

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Oak Processionary Moth originates from southern Europe but its distribution has been steadily spreading the last few years. They are invasive because of their ability to spread and establish, and the larvae can be highly irritable to human skin. The caterpillars will aggregate in large numbers, they're typically seen walking up tree trunks in 'processions' of many individuals. They'll then build extensive communal webs in the host tree. These caterpillars will only infest oak trees. These caterpillars were accidentally introduced to the UK in 2005 and their range is expanding. If you think you've seen one, report it to TreeAlert and be careful not to touch them. They move in long head to toe processions. There are no other species of moth that display this behaviour on oak in the UK.
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Traits

Can cause irritation to human skin.
These caterpillars don't do much harm to trees.

Appearance

Adults: The moths are only active for two days following emergence in late summer. They are large, with wingspans reaching as much as 3.5cm. The wing patterning is very similar to several UK species; at rest, wings are brown with a dark, wavey, thin lines that horizontally cross the wings when at rest. They camouflage well amongst the cracks and crevices of tree bark. Larvae: They feed in the treetops, but as they grow, they start to make their way down the trunk in head to toe processions. Each caterpillar is 2-2.5cm, brown-grey, with long, fine white hairs. They blend excellently to the colour on tree bark, so be careful before inspecting anything that appears to be 'moving' on Oak.

Symptoms

The caterpillars of this moth can irritate human skin and should not be touched. Trees trunks and branches may become covered in silk webbing nests. Some defoliation may occur.

Activity

Crepuscular

Personality

Order

Lepidoptera

Family

Thaumetopoeidae

Metamorphosis

Complete

Distribution

Widespread across Europe

Biological treatment

If you think you have oak processionary moths in your garden, don't try to remove them yourself! Any removal should be done by a professional contractor trained in handling toxic insects. Likewise, leftover webbing can retain the toxic hairs, so don't try to do this yourself.

Chemical treatment

Treatments should only be applied by a professional.

Attracts

These caterpillars will only use oak as a food plant.

Oak

Quercus spp.

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