Horntail wasps (woodwasps, family Siricidae) are large insects often mistaken for hornets due to their size and intimidating appearance. They are primitive members of the insect order Hymenoptera, related to sawflies, bees, and true wasps. Horntail wasps are generally harmless to people and do not sting defensively.
Do Horntail Wasps Pose a Threat?
Horntail wasps are non-aggressive and pose no threat to humans or pets. They are solitary and do not guard a nest or colony, eliminating the need for defensive stinging. Unlike social wasps, they lack a venom apparatus. They are also incapable of biting a person in a medically significant way.
The long structure on the female that resembles a stinger is actually a specialized egg-laying organ called an ovipositor. While frightening due to its size, the insect will not use it to sting. If a female is mishandled, she might accidentally prick the skin, but this is not a venomous sting and is not medically dangerous.
The Function of the Ovipositor
The long, needle-like ovipositor on female horntail wasps is used exclusively for reproduction. This specialized organ bores into wood to deposit eggs deep within the material. Females target dead, dying, or stressed trees, or recently felled timber.
The ovipositor has saw-like parts that allow the female to penetrate wood, sometimes reaching depths of up to three-quarters of an inch. When depositing an egg, she also introduces a symbiotic fungus into the tree tissue. This fungus breaks down the wood, creating a digestible food source for the developing larva. Larvae tunnel through the wood and may remain there for two to three years before emerging as adults.
Appearance and Habitat
Horntail wasps are moderately large, with many species reaching 1.5 inches in length; the Pigeon Horntail can grow up to 2 inches. Their bodies are cylindrical and broad, lacking the thin, constricted “waist” common to many other wasp species. Coloration varies but often includes black, brown, blue, or metallic dark blue, frequently with yellow or red bands.
Both sexes have a stout, spine-like projection at the tip of the abdomen, which gives them the name “horntail.” This projection is distinct from the female’s ovipositor, which is located underneath the abdomen. Horntails live in or near woodlands where host trees, such as pines, maples, or elms, are present. They are sometimes found in residential areas when adults emerge from infested lumber used in construction, but they cannot re-infest milled wood.