Well, they really aren't worms, they are caterpillars of the adult moth, the Oak Leaf Roller. The moth is about 1/2 inch long and has brown wings and brown markings.
In May, the moths lay their eggs on Texas Live Oaks. The eggs stay there for an amazingly long 10 months, until they begin to hatch in mid-March. And they are here. Now. I had my first sighting in the back yard moments ago as I almost walked right into one dangling from an oak tree in the back yard.
And they do dangle -- down from the oak trees by the gazillions (well, maybe a few less than that) and make it almost impossible to pass under an oak without having green, squishy, squirmy caterpillars in your hair, and on your clothes, and everywhere you can imagine. These little caterpillars feed on the tender new Spring growth of the oak trees through late April. They can literally defoliate an entire tree. But they are a sight to behold if stand a little to the side of them!
Then they form the pupae stage and in early May, and the moths come out and then they start laying eggs again and the whole cycle starts all over again.
While you can control them with BT, or Bacillus Thuringiensis, we've never really needed to use it. The oaks are hearty, and while I'm sure they don't like being eaten on, they bounce right back for the most part, so we just watch where we walk for a month and leave the moths alone to complete their life cycle. It's another part of Spring, much like the flowering of daffodils, quince and Texas bluebonnets.
Then there is the new oak growth and the neon-green, powdery pollen that covers everything in a thick blanket of green dust ... but that's another post!