You know that feeling you get the first time you find nits in your child's hair? I had that feeling just there now, on my evening patrol of the fruit trees. I found a ball of fluff stuck between some leaves on an upper branches of an apple tree.* I bent in for a closer inspection, and as realisation dawned my arms broke out in shivery goosebumps and I said to myself, "Oh my god, I'm going to be sick." A fat cluster of cobwebby-fine fluff had been spun between a pair of leaf clusters, full with little black dots, rather like the tiny black seeds that fall from cut roses onto your window ledges. And then I saw them; squirming lines of black and grey caterpillars inside this fluff ball, like some revolting THING out of Alien2. It was so sickening I can't even bear to search the RHS pest web pages for guidance. I just picked off the two leaf clusters and that THING between them, and dropped the lot into the dustbin. Yuk yuk yuk. And as I write this my arms itch as if caterpillars were crawling along them, infesting me. Now my head's itching. I bet yours is itching too. That's the thing with infestations, you can't escape psychological damage.
* Grafted onto a dwarf rootstock.