Aka Thaumetopoea processionea AKA Oak processionary moth AKA Eichen-Prozessionsspinner AKA irritating little wrigglers AKA bane of last summer

Despite lock down, restricting movement (these pesky crawlers con't care one jot), ramblers might end up in the woods, or even unknowingly neighboring a nest.

Some quick info:

Common name: oak processionary moth

Scientific nameThaumetopoea processionea

What does it affect?: oak species (species in the genus Quercus)

Origin: Central Europe

After last year's rather panicked taping off of trees, just what is the oak processionary moth?

The oak processionary moth is a species of moth with caterpillars that nest on oak trees (clue is in the name). The caterpillars are covered in small hairs which can cause health risks in humans (they are rather painful and can cause serious allergic reaction).

To minimise health risks:

  • Do not touch or approach oak processionary moth caterpillars or their nests. It's not that they get territorial, but rather the hairs are very fine and carry easy on the wind. Plus there's absolutely loads of them.

  • Do not let children or animals touch or approach the caterpillars or nests, per above reasons.

  • Do not try and remove the caterpillars or nest yourself, per the obvious risks and above reasons.

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What exactly do they do to the tree?

Although there is just the one generation of oak processionary moth per year they do a heck of a lot of damage for such small critters.

The caterpillars hatch in spring and go through several instars (developmental stages), eventually developing the irritating hairs. The caterpillars descend lower down the tree as they develop, stripping the tree of its leaves as they go, leaving it vulnerable and weakened.

In summer, the wrigglers retreat into nests and pupate, with the adult moths emerging in late summer.

The moths hang about for only four days in order to mate before popping off the mortal coil. The female lays her fertilised eggs high in the tree canopy and the cycle begins again.

What does oak processionary moth damage look like?

The oak processionary moth feeds and lives almost exclusively on oak trees.

An infested tree will display symptoms which include:

  • Caterpillars in procession on the trunk nose-to-tail in late spring and early summer. The procession is sometimes arrow-shaped with one leader and rows of caterpillars following.

  • Nests on trunks and larger branches of oak trees. They are made of distinctive white silken webbing that fades to a light brown colour.

  • Dislodged nests on the ground near oak trees.

(sources include: Woodland Trust / Forest Research)