An infestation of caterpillars that can trigger asthma attacks, vomiting and skin rashes has appeared in south-east England.

Oak processionary moths, in their larval stage now, have been spotted in areas that include Croydon, Twickenham, Epping Forest, Watford, Ealing and several London suburbs. Other infestations have been spotted in Bracknell Forest, Slough and Guildford.

Hairs on the moths contain toxins that cause severe dizziness, fever and eye and throat irritations, health officials have warned. The caterpillars - which feed off oak trees - have distinctive extremely hairy bodies and should not be touched. Sightings should be reported to the Forestry Commission.

The species derives its common name from the fact it lives primarily on oak trees and moves about in nose-to-tail processions, while the first part of its scientific name – Thaumetopoea processionea – comes from thaumetopoein, the irritating protein found in its hairs.

Contact can cause itching, skin rashes and, less commonly, sore throats, breathing difficulties and eye problems which are triggered if people or pets touch the caterpillars or their nests, or if the hairs are blown into contact by the wind. Nests should not be touched without protective clothing, the commission has warned.

The commission said 150 hotspots had been identified and traps to kill off the caterpillars would be set up over the next few days. Hundreds of others spots around London are to be sprayed with insecticides.

The oak processionary moth is a native of southern Europe but its range has been expanding northwards over the past 20 years and it has become established as far north as the Netherlands and northern Germany. It was first introduced – accidentally – to Britain in 2005 from eggs that had been laid on live, imported oak plants. The current infestation has probably arisen from a similar source, the commission has stated.