Oak processionary caterpillars. ...?
At the moment there is a plague of oak processionary caterpillars in our area. See link below https://www.bbc.com/news/world-europe-48880468 Although we are biking daily for shopping, exercise and pleasure we have only seen one infestation. There are many oaks planted by roadsides and forests. As soon as an infest action is spotted it is reported, logged and local councils tag the tree and try to remove or spray. The reported trees are plotted oh map and published daily in local newspaper. So far we have not been stung. Here is another link https://heavenly-holland.com/oak-processionary/ Nasty little buggers.