Tremex columba

Distinguished from other horntails by the combination of: cylindrical body shape with yellow and black abdominal stripes; female's long, visible ovipositor with protective sheath; short dorsal cornus present in both sexes. Can be confused with giant ichneumon wasps (Megarhyssa), which have extremely long, whip-like ovipositors (often exceeding body length) and more slender bodies. Distinguished from Urocerus californicus (found in Pacific Northwest) by color pattern and geographic range. Distinguished from Sirex species by abdominal color pattern and host preferences.

Large, cylindrical wasp with cigar-shaped body. Females 25-50 mm (sources vary: 25-30mm per Wikipedia, 37-50mm per Bug Eric), males smaller at 18-37 mm. Coloration ranges from light brown to dark reddish brown, with yellow and black stripes along the abdomen. Both sexes possess a short dorsal projection called the cornus at the tip of the abdomen. Females have an additional long, needle-like ovipositor projecting ventrally from the abdomen, which can be several centimeters long and is housed in a two-part sheath when not in use. Western specimens are typically paler than eastern specimens.

Deciduous forests, woodlands, and urban areas with hardwood trees. Associated with dead, dying, or weakened hardwood trees, particularly American beech, maple, elm, oak, apple, pear, poplar, hickory, sycamore, and hackberry. Requires wood infected with Daedalea unicolor fungus for larval development.

Eastern and western North America. Documented from Nova Scotia and New Brunswick south to Florida, west through Quebec, Ontario, and the Prairie Provinces to British Columbia, and south through the western United States to Mexico, Arizona, Utah, Colorado, and with scattered records from southern California. Also recorded from New Brunswick specifically.

Adults active from late summer through fall, primarily August to October. Peak oviposition activity from mid-August to mid-October. Males typically emerge before females. Adults may be found resting on foliage at eye level.

• Fagus grandifolia - oviposition hostprimary host in New Brunswick; weakened or injured trees preferred
• Acer spp. - oviposition hostmaple species commonly used
• Ulmus spp. - oviposition hostelm species acceptable
• Quercus spp. - oviposition hostoak species used
• Malus spp. - oviposition hostapple
• Pyrus spp. - oviposition hostpear
• Populus spp. - oviposition hostpoplar
• Carya spp. - oviposition hosthickory
• Platanus spp. - oviposition hostsycamore
• Celtis spp. - oviposition hosthackberry
• Daedalea unicolor - obligate symbiontwood-rotting fungus introduced during oviposition; larvae require infected wood to develop beyond first instar
• Megarhyssa macrurus - parasitoidgiant ichneumon wasp; lays eggs on horntail larvae in tunnels
• Megarhyssa greenei - parasitoidgiant ichneumon wasp species
• Megarhyssa atrata - parasitoidgiant ichneumon wasp species
• Ibalia anceps - parasitoidibaliid wasp; attacks younger larval stages at shallower depths

Minimum two-year life cycle. Eggs laid August-October, either hatching in 2-4 weeks or overwintering to hatch the following May-June. Larvae tunnel through wood, feeding on wood and Daedalea unicolor fungus; pass second winter in larval stage. Pupation occurs within the tree; adults emerge in August, with males emerging before females. Development typically takes 1-2 years total.

Females use the ovipositor to drill into wood, bracing it at a 90° angle to the abdomen, and can insert it several centimeters into solid hardwood. During oviposition, the female may die and remain stuck to the tree. Males have been observed resting quietly on foliage and can be approached closely. Emerging females may lay eggs in existing galleries, producing male-only progeny through arrhenotoky. Adults do not visit flowers; adult feeding habits are poorly documented but may include tree sap.

Decomposer of dead and dying hardwood trees; facilitates wood decay through association with Daedalea unicolor fungus. Serves as host for giant ichneumon wasps and ibaliid wasps, supporting parasitoid communities. Contributes to nutrient cycling in forest ecosystems by breaking down lignified wood.

Not harmful to humans; does not sting or bite. Occasionally mistaken for dangerous wasps due to large size and prominent ovipositor. Sometimes encountered when splitting firewood, where larvae or adults may emerge. Not considered a pest of living trees, though rarely attacks healthy trees. May introduce wood-rotting fungus that could affect timber value.

• Megarhyssa spp.giant ichneumon wasps have extremely long, whip-like ovipositors often exceeding body length, more slender bodies, and are parasitoids of horntails rather than wood-borers
• Urocerus californicusPacific Northwest horntail with different coloration and geographic range; western T. columba are paler but still distinguishable
• Sirex noctilioinvasive European species that attacks living pines; T. columba is native and primarily uses hardwoods
• Xiphydria spp.smaller horntails (~12mm) with different body proportions

Frequently mistaken for a stinging wasp due to the prominent ovipositor, which resembles a stinger. The species is non-venomous and cannot sting. The dorsal cornus is not a stinger and its function remains unknown.

• horntail
• wood-borer
• fungal symbiosis
• non-stinging
• native
• forest insect

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Bug Eric: Pigeon Horntail Wasp Ovipositing
• Bug Eric: Wasp Wednesday: Pigeon Tremex Horntail
• Ovipositing Pigeon Horntail | Beetles In The Bush
• Siricidae | Beetles In The Bush
• The ants, bees and wasps of Canada, Alaska and Greenland – a checklist of 9250 species | Blog
• Bug Eric: June 2013
• THE PIGEON TREMEX, TREMEX COLUMBA (HYMENOPTERA: SIRICIDAE), IN NEW BRUNSWICK