It is an annual summer problem in the Netherlands, but the number of complaints about the Oak Processionary moth caterpillars have soared this year, according to the specialist centre at Wageningen University which monitors the insects.

The caterpillar sheds poisonous hairs which may cause skin irritation and breathing problems. They crawl in procession over the bark of oak trees forming a moving carpet of hairs.

In some places the number of trees infected with the caterpillars has gone up three-fold, the centre said. The caterpillar, which was not native to the Netherlands until the 1980s, has been moving through northern Europe, possibly as a result of global warming.

The centre’s experts believe local authorities should be far more structured in their approach to dealing with the pest.

‘It should be coordinated on a national scale,’ biologist Arnold van Vliet told website Nu.nl. ‘This is not a problem which is going to go away and it will have an economic impact on campsites and in recreational areas. There may also be food safety concerns because their hairs end up in grain. But the ministries have not made it a priority.’