Ugh, bugs. There's something unsettling about walking under a tree that is infested with worms, none the less.
And this year, you'll notice that the Fall webworm problem seems to be worse than ever. And if left unchecked, they will kill your trees- especially the ones you may cherish the most such as pecan and walnut.
There are sprays available that can help, but it appears that true prevention should happen during the Springtime to kill eggs before the worms can become a problem.
Good suggestions on controlling webworms can be found here: