Wood wasps, also known as horntails, are large insects belonging to the family Siricidae. They often cause alarm due to their size, measuring well over an inch in length, which leads many people to confuse them with aggressive, stinging wasps. The female’s long, tail-like projection on her abdomen is particularly unsettling for those unfamiliar with the species. Horntails pose little danger to people or sound structures.
The Stinging Question
The most immediate concern about the horntail is whether it can deliver a venomous sting. The answer is definitively no, as wood wasps are non-aggressive and lack the defensive, venom-injecting stinger found in species like yellow jackets and hornets. Horntails are solitary and not prone to confrontation, unlike social wasps which sting to defend their colony.
Any perception of being “stung” is likely the result of accidental probing by the female’s egg-laying apparatus. They are harmless to humans and pets because they do not possess the chemical-laden venom associated with a true wasp sting.
Anatomy and Purpose of the Ovipositor
The structure that causes the most confusion and fear is the female’s ovipositor, an organ dedicated solely to reproduction. Its function is not defense but to drill into wood to deposit eggs deep within the tree. The ovipositor is an intricate biological tool composed of two interlocking shafts, or valves, each equipped with backward-facing teeth.
The female uses a drilling technique where the valves alternate in providing an anchor and moving forward. This push-pull, reciprocal motion minimizes the force needed to penetrate dense wood, allowing the wasp to bore nearly three-quarters of an inch or more into the sapwood. When laying eggs, the female also injects a symbiotic fungus that begins to digest the wood, providing a food source for the developing larvae.
Identifying the Wood Wasp
Wood wasps are large insects, typically measuring one to one and a half inches in body length. They possess several distinct physical traits that set them apart from true wasps. Unlike the thin, constricted “waist” of many stinging wasps, horntails have a robust, cylindrical body shape.
Their coloration varies among species, often featuring combinations of black, blue-black, or striking yellow and black patterns. A secondary feature is the “horn” or terminal spine, called the cornus, which projects from the end of the abdomen of both males and females. This spike is separate from the female’s ovipositor, which is generally located below it, and gives the horntail its common name.
Impact on Residential Structures
The presence of a wood wasp does not indicate a structural pest problem in a home. These insects primarily target dying, stressed, or recently felled softwood trees, such as conifers, to lay their eggs. They do not bore into or re-infest the seasoned, dry lumber commonly used in building construction.
If a wood wasp emerges indoors, it is a one-time event resulting from lumber that was already infested with larvae before it was milled and installed. The damage is usually cosmetic, involving round exit holes up to a half-inch in diameter in drywall, flooring, or other interior materials. This emergence does not affect the structural integrity of the building.