The Horntail Wasp (Urocerus gigas / Sirex noctilio) is yellow and black, or blue-black; large with prominent horn-like tail spine and typically measures 1–1.5+ inches. Horntail wasps are a subset of wood wasps (family Siricidae) that include some of the largest and most visually striking wood-boring insects in North America. The giant horntail (Urocerus gigas) and t.

The Horntail Wasp poses a moderate risk. Self-limiting structural infestations from lumber cause no ongoing damage. Sirex noctilio is an invasive species capable of killing healthy pine trees — a regulated pest. Adults cannot sting.

In Arizona, horntail wasps are most often encountered in the following situations: Large round emergence holes (3/8–1/2 inch) in pine or fir lumber or structural wood. Very large wasp-like insects (1–1.5+ inches) with yellow-and-black or blue-black coloring and prominent tail spine. Coarse frass. Emergence from walls, floors, or ceilings in newer construction.

The Horntail Wasp is most active during: Year-round in wood; adult emergence summer through early fall. 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. Inspect pine and fir lumber for oviposition holes before use. Report suspected Sirex noctilio infestations to the Arizona Department of Agriculture.

Structural infestations are self-limiting — seal emergence holes. Sirex noctilio in trees: contact the Arizona Department of Agriculture immediately. Preventive insecticide bark sprays for high-value pines in areas with known Sirex activity.

If you are seeing horntail 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.