Why are squirrels chewing holes in irrigation lines?

DEAR JOAN: I recently found an almost ¼-inch hole in a drip irrigation line. I couldn’t figure out how it happened and my wife said it could have been a squirrel, of which we have many.

After not believing her, I observed a squirrel appearing to be doing just that and found clear gnawing marks where it had been. Why does a  squirrel want to eat through a plastic water line?

— S. and S., San Jose

DEAR S. and S.: I trust you’ve learned two things from this incident. One, squirrels...