Oak Processionary. Every year a lot of money is spend on flaming, sucking many caterpillars to provide local relief.
The Forest Caterpillar Hunter is extinct in the Netherlands, it is widely used in the USA to keep the Gypsy Moth under control. It would be cheap and natural to bring this little beastie home.
Every year I try to get people to appreciate the notion that natural predation is to be preferred. This time I called the Dutch Ministery and Staatsbosbeheer. I send e-mails to both and I will report when I get a reply that is more meaningful then "we will study your suggestion".