Feeding by the caterpillars removes all of the leaves on some branches. However, the damage occurs so early in the season that the trees may grow new leaves to replace those lost to tent caterpillars.
In midsummer, the adult form of this pest, a downy beige moth, lays egg masses on host trees. These are dark globs that often encircle small branches, and they have a glossy finish, as if they had been varnished. Clipping off these egg masses during routine pruning is the best way to limit the number of colonies you see the following spring. The eggs hatch very early, often before blossoms are open, and the bristly black caterpillars huddle together for warmth.
The webs made by tent caterpillars function as greenhouses that help these early-season feeders stay warm, so disturbing the web puts substantial stress on the colony. You can poke holes in the tents with a stick or long-handled apple picker, and then twist to gather up caterpillars and webbing.