Looks like tent caterpillars. They can be voracious, but whether it will be a big problem depends on how many webs there are, how vigorous the trees are, and how good the weather is (if it's a dry year the trees will be more stressed and susceptible).

I've seen them in stands where they hardly seem to make a dent, and others where the trees are nearly defoliated.

They are called bag worms. Take a stick or something and break open the web. Birds with eat the caterpillars.

Those are Tent worm caterpillars which can be found on deciduous trees in the spring,. Bag Worms are usually found on evergreens in the summer and the bags look quite different than these tents.

Tent worms, and bag worms, can be controlled by spraying the trees leaves with Bacillus thuringiensis - Kurstaki early in their life but it is not effective after about three weeks from hatching. Breaking open the nest can be effective as some bird species will eat them.

https://images.search.yahoo.com/search/images;ylt=A0LEVz6Z0VVpwwA9JtXNyoA;_ylu=X3oDMTExZzQ0YmY1BGNvbG8DYmYxBHBvcwMxBHZ0aWQDVUlDMV8xBHNlYwNzYw--?p=Tent+Worms&fr=mcafee

https://images.search.yahoo.com/search/images;ylt=A0LEVxLP0VVlacAclJXNyoA;_ylu=X3oDMTExZzQ0YmY1BGNvbG8DYmYxBHBvcwMxBHZ0aWQDVUlDMV8xBHNlYwNzYw--?p=Bagworms&fr=mcafee

kimmq is kimmsr

Tent caterpillars (not bagworms, zzackey) will be controlled by all manner of critters if those tents are ripped open. Birds love them, squirrels, spiders, parasitic wasps, tree frogs, and other predators will devour them if you give them a little bit of help.

You can also use a strong stream from a garden hose to break open the nest.

The caterpillars are capable of doing lots of damage, but it's considered temporary; leaves will grow back. Repeated defoliation is very hard on the tree and you need to get rid of those nests as soon as you spot them.