Question
My Elm tree has holes all the way around the tree and up & down the tree.  The holes are like someone used a drill and uniformly drilled holes next to each other and all the way from top to bottom.  What could this be?

Answer
This is caused by a woodpecker called a sap sucker. the bird makes these holes and sap forms in the holes. insects come and eat the sap and the bird returns and eats the insects. On elm trees they really do not cause any health problems for the tree. On thin barked trees like maple the holes can be a source for fungi to enter but elms have a thicker bark and this is not a problem. If you want to discourage the sap sucker from coming you can spray the area of the bark with an insecticide and this will kill the insects and the wood pecker will stop coming. Otherwise just leave it be.