Woolly beech aphid (Phyllaphis fagi) is a + 2 mm, light green aphid that lives on and of beech trees. The aphids secrete woolly wax threads that carry the aphids with them.
The aphids live off the leaf sap; the excess sap the aphids excrete as honeydew on which sooty mold forms during the season.
In autumn, female aphids lay eggs in the bark crevices and buds of beech trees. In spring, the larvae hatch and often form colonies on the undersides of leaves.
Control is generally not necessary.