Answer: I suspect what you are seeing are fall webworms. Fall webworms, it turns out, are misnamed on both counts.
They aren't worms but caterpillars, the larvae of an inch-long white moth. The moth lays its eggs on the undersides of the leaves of trees. The eggs hatch into caterpillars, which start dining on the foliage and spinning out a protective, silky web.
And as anyone who's driven down a heavily wooded street lately will attest, webworms don't just come out in the fall.
Spraying with a pesticide will kill the caterpillars, if you can hit them. But if your tree is large, and the webs are high, it might be impossible. There is a family of natural pesticides, known as "Bt" products, that will control webworms. Made from a toxin produced by the bacteria Bacillus thuringiensis, they are available at most garden centers.
Simply poking a hole or two in the web, using a long pole or a water sprayer, can also do the trick. The web is the caterpillar's protection against predators such as wasps and birds. If you break the web open significantly, the weather and the birds will put an end to them. And, always watch out for power lines when poking around in trees with big poles.
Best wishes with your webworms.
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