The horntail wasp, a member of the Siricidae family, is a large, striking insect often mistaken for a giant stinging wasp or bee because of its size and coloration. These insects, sometimes called wood wasps, can reach lengths of up to two inches, which often causes alarm. Despite their intimidating appearance, horntail wasps are generally harmless to humans and cannot deliver a defensive sting. Their abdominal features are designed for a purpose unrelated to defense.
Physical Features and the Non-Stinger
Horntail wasps typically display robust, cylindrical bodies that lack the narrow “waist” found on many other wasp species. Their coloration often includes black, brown, or metallic blue with distinct yellow or reddish markings, a pattern that mimics stinging insects to deter predators. Both male and female horntails possess a short, stout spine at the end of their abdomen, which gives the insect its common name.
The feature that most often causes fear is the long, spear-like appendage found only on the female, which is an ovipositor, not a stinger. This specialized organ is an egg-laying tool used to bore into wood, not a weapon for injecting venom. It contains two interlocking valves, allowing the female to drill deep into timber to deposit her eggs. Because males lack this apparatus, they have no physical means to sting.
Assessing the Danger to Humans
Horntail wasps are non-aggressive insects that do not sting or bite people. The female’s ovipositor is rigid and designed solely for boring into wood, meaning it cannot function as a defensive stinger. This structure is incapable of injecting venom, as horntail wasps do not produce or carry venom like other members of the Hymenoptera order.
If a female horntail lands on a person, she is unlikely to use her ovipositor defensively, as her instinct is to seek out wood. A person might experience a purely mechanical “poke” if a female attempts to bore into clothing or skin, but this is an extremely rare and non-venomous event. The male horntail, having no ovipositor, poses no threat. Any perceived danger is due to their large size and visual similarity to other stinging insects.
What They Damage Instead of People
The sole focus of the horntail wasp’s life cycle is wood, specifically during the larval stage. The female uses her ovipositor to drill into a tree and deposit her eggs, typically selecting trees that are dead, dying, stressed, or recently cut. When she lays an egg, she also introduces a symbiotic fungus, such as Amylostereum, into the wood.
The larvae hatch and tunnel through the wood, feeding on the tissue conditioned by the fungus. Larval development can take one to three years before the adult chews its way out, leaving a round exit hole approximately 1/4 inch in diameter. They do not re-infest seasoned, dry lumber, so they are not a structural threat to established buildings. However, adults can occasionally emerge inside homes if the construction lumber was milled from an infested log that was not properly dried.