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The government warns that oak processionary moths are spreading and can cause allergic reactions.Picture credit: Josy Cungs (SIP) 

When the caterpillar hatches at the end of April, beginning of May, it goes through 6 development stages. They are very hairy. First they turn yellow-brown, then bluish-black. In their third development stage, they have reddish brown velvety hairy patches at the rear which build urticating hairs and barbs that contain the nettle poison Thaumetopoein. They reach up to 4 centimetres at their last development stage and produce more and more of these poisoned barbs.

The caterpillars live in families and gather in leaves.

Mid-June is the critical period

In mid-June, they build the typical nests at the trunk or in branch forks. These constructions can be up to 1 metre long and are filled with excrement. They are the resting place for the caterpillars. The caterpillars leave in great numbers to get food (hence the processionary name). Pupation happens in July, and afterwards the nests, which still contain the urticating hairs with the poison, should not be touched.

Danger for humans

The urticating hairs with the barbs can cause allergic reactions, such as itching and dermatitis. In some cases, it can lead to irritation of eyes or lungs, and to fever or dizziness. Pets can also be affected.

The caterpillars are often found in undergrowth and can stick to clothes and shoes. The nests are also dangerous, as they contain the poison, which is active for a long time.

How to protect yourself

  • Don’t touch the caterpillars or moths;
  • Tell kids about the danger and don’t let them play under trees which are affected;
  • After contact, wash clothes and shower;
  • Take care not to bring any urticating hairs into your home;
  • If infected, wash out the urticating hairs with soap. Hair which is deep in the skin should be removed with tweezers;
  • In serious cases, a doctor should be consulted;
  • It can be treated with antihistamoin or cortison creams;
  • Cold compresses can alleviate the symptoms.

More information here