Oak processionary moths are inconspicuous moths. The caterpillars usually only become dangerous for oaks if they are infested for several years in a row. However, humans should not take the animals lightly.

Recognize oak processionary moths

The adult butterflies of the oak processionary moth (Thaumetopoea processionea) are quite inconspicuous and can be recognized by the following features:

  • rather inconspicuous ash to brown-grey colouration
  • Wing span of up to 36 millimeters
  • Flight times: late July to mid-August

The nocturnal caterpillars of the moths, on the other hand, show an extremely striking appearance:

  • orange when hatched in spring
  • from the second instar: gray-green with a lighter area on the sides
  • from the third stage of development: hair
  • long hair up to about one centimeter (not dangerous)
  • up to 700,000 stinging hairs on brushes: 0.1 to 0.3 millimeters long
  • Stinging hairs and older skin of the caterpillars cause painful skin reactions (itching, swelling, blisters)
  • Hair falls on clothes
  • are spread by the wind up to 500 meters

What to do if discovered?

If you spot a caterpillar, the best thing to do is keep your distance or run away. To protect others, you should report the location of the oak tree.

These are the competent authorities

  • Forestry office/green space office/office for urban greenery,
  • regulatory office,
  • health department.

A phone call or an email is usually sufficient. In order for the authorities to be able to secure the area, you should report the following information:

  • location, date and time
  • Degree of infestation, as far as can be seen
Note: If you are taking a picture for yourself or the authorities, you should keep your distance when taking the picture.

What to do if you suspect

If you suspect that the oak processionary moth has nested in a tree, you should

  • approach it with extreme caution
  • Cover your skin all over your body, including your hair
  • try to take a picture that clearly shows the caterpillars

After the inspection, proceed as follows:

  • Wash clothing including gloves at at least 60 degrees Celsius
  • shower incl. hair wash
  • Thoroughly clean shoes and goggles
  • Dispose of mouth and nose protection in a plastic bag

What to do in the event of an acute infestation?

Since contact with the stinging hair is associated with unpleasant consequences, you should under no circumstances come into contact with the hair:

  • Do not touch caterpillars
  • Do not touch nests or caterpillar debris
  • keep a distance of several meters from the tree (the stinging hairs are whirled up by the wind)
  • do not pick up anything from the ground around the tree
  • do not pick up or remove old nests and caterpillar residues (harmful effect over several years)
  • close windows and doors

remove caterpillars

Due to the danger posed by the stinging hairs of the oak processionary moth, you should not remove caterpillars and nests yourself. We strongly advise against hosing down the nests or burning the caterpillars, as such measures only spread the stinging hairs in all directions.

You should therefore either contact a pest controller directly or ask the responsible public order office or green space office for a professional company. Because the experts not only have the necessary protective clothing, but also know the appropriate methods for removing caterpillars or nests with the least possible spread of stinging hairs.

Note: If the infested oak is on your own property, you must bear the cost of removing it yourself.

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