I recently purchased a home with a nice box elder in the yard. I noticed that some of the branches were dead and proceeded to cut them out. This year, some of the branches died just as the leaves were about half the size that they reach during the spring. Is this a bug or fungus problem? I noticed several large black ants that seem to like hanging out in the tree, but I haven't seen enough to warrant the amount of dying wood. Please help!?

I am afraid that may just be the way box elders are. They tend to be short lived. This is tough advice, but you might be better off to remove it and replace it with something that will be a nicer tree.