There are white, fuzzy objects on the branches of my maple tree. Are they harming the tree?

FAQ
Question: 

There are white, fuzzy objects on the branches of my maple tree. Are they harming the tree?

Answer: 

The white, fuzzy objects on the branches of your maple tree are wooly alder aphids.  (The insect is also known as the maple blight aphid.)  Wooly alder aphids feed on the sap of maple trees from bud-break until late June.  Then winged adults, some with abdomens covered in white fluffy wax, are produced in the colonies.  These winged migrants readily fly when disturbed and create the illusion of tiny masses of cotton floating through the air.  The winged adults leave the maple tree and fly to alders where they establish new colonies on the secondary host.  Wooly alder aphids require both maple and alder trees to complete their life cycle.  

While the presence of white, fuzzy colonies of wooly alder aphids on a maple tree may cause alarm, they don’t cause serious harm to infested maples.  (Damage is usually limited to the loss of some leaves.)  Large wooly alder aphid populations usually collapse from predation and parasitism.  Control efforts are not necessary.