No and no.

Your best option is to try to disturb the nests with a sharp stream of water or an long handled tool of some sort. You could even clip off the ends of the branches where the nests are (they will be Fall Webworms at this time of year).

Fall Webworm caterpillars are a favorite food for many, many different kinds of predators. Breaking open that webby nest makes them easy prey.

This appears to be a bad year for the webworms in much of the country. This, too, shall pass.

If you have nests of leaf eating thingys in your trees and shrubs it will be a cousin ot the Eastern Tentworm, the Fall Webworm. While having the webs in trees may be somewhat of an eyesore there is no good reason to prune the webs out of the trees, something that can cause more damage to the tree then the webworms will. Spraying a dormant oil now is not a good idea since it will cause more damage to the tree then will the webworms.
If the webworms are too old for Bacillus thuringiensis - Kurstaki to control simply poking large holes in the webs will allow access for the many predators, both birds and other insects.

Is this web worm the thing that is in my pecan trees? We bought a tiny strip of land from the neighbor behind us to extend our city lot gardening options. The area has three Mississippi Giant pecan trees, one already bearing. And it is the one with a web on it.

Will spraying with a strong blast of water help get rid of that? I was wondering how to get up there to deal with it.

This is a picture of my "back forty" as we call it...still fairly wild with two large sasanquas and plantings of old fashioned azaleas. The fence gate is there to allow visiting with the neighbor lady. I have purchased 35 star jasmines to plant along the chainlink fence as a hedge, like we saw the plants used in Tuscany.

Probably the fall webworm; they seem to love oaks, hickories, pecans, and the like. And there are LOTS of them this years! Again, your two best options are to snip the tips of the branches where the nests are if you can reach them, or to disturb the nests so that predators can get to them.

Oh, third option is to simply not worry about them!

Maybe I'll collect them and bring them to the wildlife center I volunteer at. I'm sure all the birds will enjoy them.

If you have any squirrels or other animals ('possums, raccoons) at the wildlife center, be sure to let them have some of the caterpillars, too. They are another good source of proteins and other good stuff.

Thanks... but I really doubt the squirrels are going to eat them. And our coons and opossums are on diets that we had experts in the field specially formulate for us with excellent results. I also doubt they'd eat them when they have access to more palatable and substantial meat.

Keep in mind that pruning off the branches where these webs are is more destructive then the Fall Webworm is. While they may eat the leaves off those branches the leaves will grow back next spring. The Fall Webworm will not kill the branches as pruning them off will.

What happens when a pruning cut is made at the tip of a branch? (This is for Kimmsr)

Dormant buds behind the cut are triggered to activity by the redirection of hormones that exist in those tips. In a matter of a few days, new foliage may grow to replace any that were lost. That is why pruning is a growth generating activity.
We prune to shape a plant, to remove dead, diseased, dieing, or infested parts. We also prune to redirect growth and to stimulate growth.

Excessive pruning can cause a flush of growth that hasn't had time to harden off in preparation of winter. However, snipping of branch tips here and there over the plant body is not harmful. Rather, it is much better for the tree, in terms of physiological response to damage, to have a bit of pruning done as opposed to the feeding of hundreds of caterpillars.

Since any damage done to the tree branch by the Webworms is merely cosmetic, why prune? Prune when necessary but do not prune if it is not necessary and in the case of the Webworm it is not necessary.

Got to have the last word again ay kimmsr?? Even if it is totally unnecessary?? You're not saving the world you know??

Pruning is the easiest way and it wont hurt anything.