I started taking pictures of webworms a few weeks ago. The weather had started getting warm and I was seeing evidence that it would be a bad, bad year again, but then we had quite a few gloomy, rainy days, which slowed their growth.
When it's hot and sunny, they are prolific. Cold and rain, not so much.
So the first question you have is what are webworms?
They're disgusting catepillar-creatures who are the larvael form of a moth. The moth lays the eggs, the eggs hatch to webworms. As the worms grow, so does the web. If there are enough of these little buggers they can cover, and eventually kill a tree.
One year I did see these things take over a hickory tree on the school property behind our house, and the tree did live, and it did grow quite a bit the next year. The problem with webworms, other than they denude a tree and look disgusting, they tend to attack nut trees. And in this part of the country that's our pecan trees.
More webworms, less pecans to harvest. This is bad business.
We've had webworms on our river birch once. We cut the branch off. But let me tell you that they scurry away, so be prepared with chemicals or fire to kill them once the branch is down.
Personally, I'm a fan of fire versus chemical irradication. With fire, you have to catch them in their early stages when they are barely formed in the crook of a tree branch. With chemicals you have to spray into their web nest, which can be difficult.
If you happen to be driving across the country this summer and you see these nasties in the trees, you now know what they are and why they are so difficult to get rid of.
This has been a Gardening 101 public service announcement.