About 1 inch long
Usually dark brown with yellow stripes. The abdomen is tipped with a long thin appendage called an ovipositor.
Horntails are characterized by the long, thick ovipositor extending from the abdomen. This ovipositor is used to lay eggs and is not a stinger; therefore, the wasp cannot sting. These insects develop inside wood and are an occasional concern in homes because they emerge from wood used in the construction of a home. The oval exit holes in wood are about ¼-inch in diameter, and these may be located in materials that adjoin infested timbers such as hardwood floors, carpeting, linoleum, wallboard, etc. The female uses her ovipositor to deposit eggs deeply into the wood of coniferous trees weakened or dying because of fire, disease or other injury. Larvae chew cylindrical tunnels within the wood, packing them with frass from their borings. The life cycle from egg to adult ranges from one to three years so adults may not emerge until two or three years after home construction. Since horntails are unable to reinfest seasoned wood, their damage in structural timbers is generally of little concern.
Horntails do not infest seasoned lumber, rather they are already developing inside the lumber used in the construction of a home. Most commonly, their presence is seen in the poorer grades of lumber which may not be properly seasoned, such as studs, joists and subflooring. They attack both softwoods and hardwoods. Occasionally, horntails emerge from firewood carried into and stored indoors.
Ideally, if wood is properly kiln dried, no horntails would survive, and the wood used in construction would be infestation-free. Once the horntails begin emerging, no treatments are needed as the emergence will soon be over. Badly infested pieces of wood may require replacement or cosmetic repairs (to exit holes), but the wasps cannot reinfest the seasoned wood in homes and buildings.