Do caterpillars excrete something special that can heal plants after munching on them?

I have a pot that I have been growing mints in for the last 3 summers. They die back in winter and come back every spring. This year I had some really sad looking mints. They were long stalks with small skinny leaves. And it was sparse looking. Well one caterpillar got in my pot and in one day, it wiped out all the leaves only leaving the stalks. It looked like tall skinny toothpicks. Funny thing is by the end of the week all the leaves grew back, bigger and thicker and even more stalks grew.

You would think that someone gave it miracle grow. In two weeks time it is tall and full. I had given up on it. Especially after the caterpillar filled his tummy. So it had me wondering if perhaps the caterpillar, by natures design, excrete something to generate growth on plants.