Some 13 children have been hospitalized in northern Switzerland after developing serious allergic reactions on a school trip.
The children, aged between 9 and 11 years old, reported irritation to the skin and eyes as well as breathing difficulties, Swiss police reported on Wednesday evening. Three of the children were transported to hospital in an emergency helicopter.
Police said the cause of the incident, which occurred near the village of Rünenberg south-east of Basel, was likely oak processionary caterpillars.
The caterpillars contain venomous hairs which can easily become airborne and spread with the wind. The hairs are known to cause irritation and breathing difficulties if inhaled.
The moth species is often found in oak forests across central Europe.