The wood wasp, also known as the horntail, is a large insect often mistaken for dangerous stinging pests like yellow jackets or hornets. Belonging to the insect family Siricidae, wood wasps are overwhelmingly harmless to humans. Their primary focus is wood, where they complete their life cycle, posing a threat mainly to certain trees and raw timber.
Identifying the Wood Wasp
Wood wasps are robust insects measuring between 1 and 1.5 inches long. Unlike many stinging wasps, their body is cylindrical and lacks the thin, noticeable constriction or “waist” between the thorax and abdomen. Coloration varies by species, often featuring combinations of black and yellow, or a striking metallic dark blue or black. The feature causing the most concern is the long, spear-like appendage protruding from the female’s abdomen. Females are typically larger than males and possess this pronounced structure, which fuels the misconception that the insect is venomous or aggressive.
Why Wood Wasps Do Not Sting Humans
The alarming projection seen on the female wood wasp is not a defensive stinger but an ovipositor, an organ specifically designed for laying eggs. Wood wasps do not sting because they lack the necessary biological structure and venom. The true stingers found in social wasps and bees are highly modified ovipositors that have evolved to include venom glands. The female uses her hardened ovipositor to drill deep into wood to deposit her eggs, a process that can take a considerable amount of time. The male wood wasp lacks this appendage entirely and is incapable of stinging. The wood wasp is classified as a nonstinging insect and is considered harmless to human health.
The True Damage: Threats to Timber and Trees
The actual danger posed by wood wasps is exclusively directed toward wood, specifically trees and raw lumber. Female wood wasps target stressed, dying, or recently felled trees, as the wood needs sufficient moisture for the larvae to develop. When laying eggs, the female also introduces a symbiotic fungus that conditions the wood and serves as a food source for the hatching larvae. The larvae then bore long, tightly packed tunnels, known as galleries, deep into the wood as they feed and mature.
This larval stage can last for a year or more, resulting in extensive internal damage to the tree or log. However, once the wood is kiln-dried and incorporated into a structure as finished lumber, the environment becomes too dry for re-infestation. Wood wasps emerging inside homes are typically hatching from lumber infested before the house was built. While emerging adults chew a clean, circular exit hole (generally 1/8 to 3/8 inch in diameter) through materials like drywall or flooring, the damage is cosmetic. The insects cannot re-infest the dry, structural wood of the home, meaning the threat to the building’s integrity is minimal.