Oak Processionary Moth

Oak Processionary Moth

Thaumetopoea processionea

Appearance

Rentokil image of an Oak Processionary Moth
  • The oak processionary moth is a rather inconspicuous, grey-brown butterfly (active from mid July until the beginning September). It's wingspan is 25 to 30 millimetres.
  • The caterpillars of the oak processionary moth have a single dark stripe down their backs. They are also covered in tiny hairs which contain a defensive toxin. These can cause severe allergic reactions if they come into contact with people and pets. Medical specialists warn against any contact with the caterpillars and their nests, as expert pest control treatment is required for safe removal.

Lifecycle

  • The Oak Processinary moth lays between 100 to 200 eggs on oak tree branches from July till early September. The eggs are laid in rows, in a single layer called a plaque. These are protected by greyish scales and remain on the oak branches over winter.
  • Between April and May the caterpillars emerge and feed together in groups. When not feeding they congregate in communal nests made of white silk webbing, which are spun under branches or on the trunk of the trees. They follow one another head-to-tail in long "processions" to and from the nests, which gives rise to their name.
  • Then between July and September the caterpillars pupate inside the nest and emerge as adult moths. Their colouring provides effective camouflage against the bark of oak trees, on which they rest.

Habits

  • The oak processionary moth is native to southern and central Europe. In recent years however it's reach has extended northwards, probably as a result of climate change. It is now firmly established in Germany, Netherlands and France. With colonies recently being discovered in parts of London.
  • The oak processionary moth caterpillars feed mostly on species of oak, including English, Sessile and Turkey. Hornbeam, hazel, beech and birch trees have also been affected, when situated close to an infected oak tree.