My desert willow is under attack!
I recently bought a house with a beautiful desert willow out front. Over the past few weeks, I've noticed that something is stripping the leaves off. They don't appear to be eaten - they are instead left at the base of the tree in a pile, and from the pile is a trail of more leaves that goes about five feet before petering off.
The leaves each seem to be cut off near the base in a clean, straight line. I've briefly examined the worst areas in the morning, early afternoon, and early evening, but haven't found any conspicuous insects or other animals. The trail of leaves just leads toward the center of the yard, and I can't find any holes or nests nearby.
Any idea what this could be and what I could do about it? Roughly a third of the tree has already been completely defoliated. This tree is the jewel of my front yard and I don't want to lose it!