They exude a sticky sap, too. My house was surrounded by them ( the local farmer seems to like them). Much as I love trees if I had my time again I’d live in a house as far away from trees as possible. I never sit in the garden, just spend my life sweeping up leaves. Last week the pines started shedding needles. The Holly has been dropping leaves for ages and I can’t let the dog into the garden as they’re so sharp and prickly. The Silver birch is now dropping catkins and soon the little seeds will be everywhere. But I think, of all of them, the Sycamores were the worst.