Wood wasps (family Siricidae), also called horntails, are large, robust wasps that are often mistaken for hornets due to their size and the prominent spine at the tip of the female's abdomen (the ovipositor, used for egg-laying, not stinging). In Arizona, several species are present, including the pigeon tremex (Tremex columba) and various Sirex species that attack conifers. Adults are impressive insects, ranging from 3/4 to 1.5 inches in length, with a cylindrical, wasp-like body in black, blue, or orange-and-black coloration. Females use their long ovipositor to drill into stressed, dying, or recently dead trees and inject eggs along with symbiotic fungi (Amylostereum species) that help break down the wood for larval nutrition. Larvae bore deep, round tunnels through the heartwood for one to three years before emerging as adults. In structural settings, wood wasps occasionally emerge from lumber milled from recently killed or stressed conifers — the larvae complete development in the wood and emerge through round holes after the lumber is installed in a building. These structural infestations are self-limiting (one generation) but can be alarming.
👁Warning Signs
Large round emergence holes (1/4–1/2 inch) in softwood lumber or structural wood. Large wasp-like insects (3/4–1.5 inches) with a prominent tail spine emerging from walls or floors. Coarse, packed frass in tunnels. Most common in newer construction using recently milled lumber.
⚠Health & Property Risks
Structural infestations from lumber are self-limiting — no ongoing damage after the initial generation emerges. Tree mortality in stressed conifers. Alarming appearance but adults cannot sting humans.
Prevention Tips
Use kiln-dried lumber in construction — kiln drying kills any larvae present. Inspect softwood lumber for signs of infestation before use. Maintain tree health to prevent attacks on living conifers.
🛡Professional Treatment
Structural infestations are self-limiting — no treatment needed beyond sealing emergence holes. Tree infestations: remove and destroy heavily infested trees. Insecticide bark sprays for high-value trees at risk.
Frequently Asked Questions — Wood Wasp
The Wood Wasp (Siricidae family) is black, blue-black, or orange and black; cylindrical with prominent tail spine and typically measures 3/4–1.5 inches. Wood wasps (family Siricidae), also called horntails, are large, robust wasps that are often mistaken for hornets due to their size and the prominent spine at the tip of the female's abdomen (the ovip.
The Wood Wasp poses a moderate risk. Structural infestations from lumber are self-limiting — no ongoing damage after the initial generation emerges. Tree mortality in stressed conifers. Alarming appearance but adults cannot sting humans.
In Arizona, wood wasps are most often encountered in the following situations: Large round emergence holes (1/4–1/2 inch) in softwood lumber or structural wood. Large wasp-like insects (3/4–1.5 inches) with a prominent tail spine emerging from walls or floors. Coarse, packed frass in tunnels. Most common in newer construction using recently milled lumber.
The Wood Wasp is most active during: Year-round in wood; adult emergence summer (June–September). Arizona's warm desert climate can extend activity periods compared to other states, so year-round vigilance is recommended in the Phoenix metro and surrounding areas.
Use kiln-dried lumber in construction — kiln drying kills any larvae present. Inspect softwood lumber for signs of infestation before use. Maintain tree health to prevent attacks on living conifers.
Structural infestations are self-limiting — no treatment needed beyond sealing emergence holes. Tree infestations: remove and destroy heavily infested trees. Insecticide bark sprays for high-value trees at risk.
If you are seeing wood wasps repeatedly, finding evidence of an established population, or if DIY treatments have not resolved the issue within a week or two, it is time to call a professional. Pest Control Bros offers free inspections and same-week service across the Phoenix metro area — no contracts required.
Dealing with Wood Wasp?
Pest Control Bros LLC serves Maricopa, Chandler, Casa Grande, Tempe, Gilbert, and Mesa. No contracts. Free inspections. Same-week service.
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