RHS: Woolly beech aphid
Woolly beech aphid is a sap-sucking insect that can make the foliage of beech trees and hedges sticky with the honeydew it excretes.
Royal Horticultural Society
Woolly Aphids: Tips For Woolly Aphid Treatment
Although woolly aphid populations rarely get large enough to harm most plants, the distorted and curled leaves they cause and leave behind can certainly become unsightly.
Gardening Know How