Cottony maple leaf scales, Pulvinaria acericola, are one of several ‘cottony’ scales in the genus Pulvinaria. Cottony camellia scale and cottony maple scale. Females produce cottony white ovisacs in spring then die. These are pretty easy to find if you look up at the undersides of maple and dogwood leaves. I did not see any crawlers yet but once they hatch you could use horticultural oil to reduce crawler abundance.