Question
QUESTION: I live in the Chicago area.I have a young maple planted from a sapling four years ago that is now about 12-15 feet tall. It looks very healthy except many of the leaves have small red bumps all over them.  They can be brushed off, but they often take the part of the leaf with them where the bumps were attached. This is the second year this has happened.  Not every leaf is affected, but many are, often in clusters.  This year I noticed that the leaves had the red bumps on them immediately after they sprouted in spring.  What is this?  Is it serious?  Can it be remedied?  I really love my tree as this is a new house and has no mature trees, but if the tree has to come down, better now than later when it is more fully rooted and developed.

ANSWER: These are insect galls on the leaves. They cause no real health  problems for the tree. The worst that can happen is the leaves will have brown spots on them which does not effect the growth of the tree. The tree could be sprayed with an insecticide but it is not worth it since they do very little damage.

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QUESTION: Is this a problem that will continue to get worse year after year or is it simply a coincidence that it happened two years in a row?  I notice that there are often black ants crawling on the tree, is this what came out of the galls(What are galls? Are they like eggs?)  

Answer
The insect lays its eggs and secretes a chemical on the leaf which causes the leaf cells to form a growth (gall) over the egg protecting them. This is a tiny insect and the gall will dry up and the egg hatches and there is a spot on the leaf left where the gall was. The ants are probably feeding on the insects and did not come from the galls.
Insect populations build up and their predators also build up but lag a year or so in population. That is why there are more galls some years than others. The number will go up and down depending on the population and the weather.