The amount of rain is not the reason you have these, although when it is as dry as it has been for two years now around here I have seen far fewer of these than in more "normal" years. Maybe, possibly the Fall Webworm, a cousin of the Eastern, and Western, Tentworm caterpillars.
The best means of control, if applied in the first 3 weeks of their life, is Bacillus thuringiensis - Kurstaki sold as Dipel, Thuricide, or a store brand.

Here is a link that might be useful: Fall Webworm

Try taking your hose to them, with a strong spray of water aimed at disrupting those nests and scattering the caterpillars. These insects have many natural predators and parasites, but those webby nests protect them.