Question
Our black walnut tree is 50-60 feet tall.  We have too mnay to caount on our property.  We've found clusters of furry worms hanging together, much like a wasp nest or bee cluster.  They are stripping the leaves from the stems.  We've found some on the graound & they don't seem to be furry at all.  I understand fire can be damaging to the tree.  We are very concerned for the rest of our trees.  What can we do.

Answer
Sounds like Walnut Caterpillar. Datana integerrima (Grote & Robinson) Lepidoptera: Family Notodontidae. This insect attacks black walnut, butternut, pecan, hickory, and on occasion, oak, willow, birch, honey locust and apple. Their defoliation can cause serious harm to young,, newly transplanted trees but they are not serious on old, well-established trees.

Newly eclosed (揾atched?or emerged from the egg) larvae have black heads and are generally light green, gradually changing as they grow to become reddish brown or purple with white stripes. As worms approach maturity, they darken, becoming almost black and at that time are covered with long, fuzzy, white hairs. The worms eventually reach a length of up to 2 inches. Larvae behave oddly when threatened, arching their fore- and hind-legs in a defensive posture. Worms are gregarious, feeding in large groups, but they do not form webs about themselves as do the tent caterpillars.

Chemical control is seldom necessary, especially on large, well-established trees. Tree mortality due to this pest is rare, but small, newly planted trees that are infested and under drought stress could be damaged. Chemical applications should be made as soon as groups of larvae appear. Some insecticides that can provide control for these colony feeders are certain formulations of carbaryl, cyfluthrin, acephate, neem and Bacillus thuringiensis (Bt).
Bt is an insecticide that the insect has to feeed on the leaves with the Bt on it  so younger caterpillars are the target. The other insecticides are contact insecticides and kill when the spray is applied to the caterpillars.
On large trees it usually takes special equipment to reach the foliage but as the caterpillars grow they will migrate down on the trunk in groups and these can easily be sprayed with a contact insecticide. The hardwoods have the capability to leave out again after they have been defoliated so I would expect the tree to put on new leaves after the caterpillars have gone. The caterpillar will not kill the tree but can cause growth loss and reduction in nut production. Check with your local nursery/garden type store for on of the contact insecticides.