The oak processionary caterpillar

Thaumetopoea processionea


Climate change favours the occupation of new habitats by certain animal species, such as the oak processionary caterpillar. This thermophilic butterfly is a lepidopteran pest, specific to oak trees.


The oak processionary is a nocturnal moth that flies between mid-July and September. The caterpillar develops in autumn and hatches at the beginning of the growing season, between April and May. It then goes through 6 stages of development to reach pupation (chrysalis) around June. From the 3rd larval stage, the caterpillar releases highly allergenic stinging hairs into the air, which can cause skin damage.


Development cycle

The nests of the oak processionary can be observed as of the 5th stage of development (mid-June) on the trunk or on the main branches of the oak. The caterpillars leave the nests in "processions" (hence the name) to feed. Even after the moth has emerged, the nests with the remains of moults and droppings remain in the trees. The stinging hairs found in them retain their allergenic character even several years after the caterpillars have left.

Impact on human health

The stinging hairs - or stinging bristles - can cause an allergic reaction of varying severity depending on the case: itching that can take up to two weeks to disappear, oedema, eye or respiratory damage (asthma attacks, etc.). Favourable weather conditions and air currents favour the transport of stinging hairs over long distances.


How to protect yourself?

  • Do not touch the caterpillars or the nests, even if they have fallen to the ground.
  • After contact with the hairs, remove clothing and wash it in the washing machine. Take a shower and wash your hair thoroughly.
  • Rinse attached hairs from the skin with soap and water. Strongly attached hairs can be removed (tweezers, adhesive tape).
  • In case of severe reactions (ingestion, eye contact, respiratory problems, ...), see a doctor promptly.
Actions taken by MONDORF Domaine Thermal to fight against this plague:
  • Installation of nesting boxes for tits. A family of tits can eat up to 500 caterpillars per day on its own.
  • Mechanical removal of nests by a specialist.
  • Installation of pheromone traps. The moths are attracted during their mating period and are caught in these traps. From July to September, this method makes it possible to limit and reduce their proliferation until they disappear.
  • Treatment (according to ministerial authorization).