Weathering isn't the only cause of the sandblasted look that old barns and old wood fences acquire. Many types of paper wasps seek out dead wood as a source of raw materials, chewing up the wood fibers to make pulp for new nests. Protective finishes prevent insect damage and protect wooden fences and other structures from ordinary weather damage.
Many species of social wasps living in the U.S. build large communal nests. Paper wasps, a reddish-brown species, build a flat nest made from a single layer of paper cells. Yellowjackets build paper nests underground and construct several layers in their buried chamber. Hornets build distinctive multilevel nests enclosed in protective paper covers. The European paper wasp colonized the U.S. only recently and was first found in Boston in 1970. This wasp resembles the yellowjacket but prefers to build its nest in dark spaces, including mailboxes, wall cavities and barbecue grills.
Wasps gather fiber for their nests by tearing small splinters from exposed wood and mixing the chewed cellulose with their saliva. Spread on the nest as a wet glue, the wood pulp dries as a tough papery cell wall built in a honeycomb pattern. Wasps use nests for only one season. Workers die from cold weather in fall and winter, but queens and drones emerge from winter dormancy to mate in early spring. Fertile queens begin new nests and raise the first generation of workers. Paper wasp nests might contain 400 cells at the season's end, but yellowjacket nests sometimes hold 15,000.
Adding a coating of paint or wood sealant prevents the slight damage paper wasps cause. Unprotected wood weathers and splinters, allowing wasps to gather loose fibers easily. Holes in bare wood sometimes mark the presence of a different insect, the carpenter bee. The size of a bumblebee, the carpenter bee chews a short tunnel in dead wood for a nesting site. Carpenter bees seldom cause any serious damage and are easily repelled by paint, wood stain or preservatives.
Wasps gather nesting materials from many natural sources, so painting your fence won't eliminate wasps near your home or in your garden. Many species of social wasps only become aggressive when their nests are threatened. Wasps of all sorts qualify as beneficial insects, since caterpillars and other damaging insects become food for wasp larvae. Removing large wasp nests requires protective clothing and an insecticide spray containing pyrethrins for quick knock-downs on contact. Any spray designed for exposed nests also works on underground colonies. Spray entrance tunnels thoroughly after dark, the Washington State University Extension suggests. Turn off your flashlight first, because emerging wasps may follow the light.