Tremex

Jurine, 1807

woodwasp, horntail

Species Guides

Tremex columba(pigeon tremex)

Tremex is a of woodwasps ( Siricidae) containing approximately 33 with a primarily Holarctic distribution. These large, cylindrical are characterized by females possessing a prominent, spear-like ovipositor used to bore into hardwood trees and lay . Unlike their relatives in the Siricinae, Tremex species associate with the white-rot fungus Cerrena unicolor rather than Amylostereum. The larvae tunnel through wood and feed on both the fungus and decayed wood material. Though they appear intimidating due to their size and visible ovipositor, they are non-venomous and pose no threat to humans.

Tremex columba by (c) Bill Keim, some rights reserved (CC BY). Used under a CC-BY license.

Tremex similis by the Smithsonian. Used under a CC0 license.

Pronunciation

How to pronounce Tremex: /ˈtɹɛmɛks/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from other Siricidae by association with Cerrena unicolor fungus rather than Amylostereum. Distinguished from Urocerus (giant wood wasps) by preference for hardwoods versus conifers, and generally smaller size. The combination of cylindrical body, visible cornus, and female's long ovipositor separates Tremex from most other . T. columba, the most common North American , can be identified by its widespread distribution and preference for maple, beech, and elm.

Images

Habitat

Dead, dying, or weakened hardwood trees. Females seek out wood already infected with white-rot fungi, particularly Cerrena unicolor, for oviposition. Found in forested areas, woodlots, and occasionally urban settings with suitable trees.

Distribution

Holarctic distribution: North America (Canada, United States, Mexico), Europe, and Asia. Individual have more restricted ranges; T. columba occurs from Nova Scotia and Quebec south to Florida and west to Mexico, Arizona, Utah, and Colorado. T. fuscicornis is native to Europe and Asia, introduced to Chile. Japanese fauna includes eight species.

Seasonality

emerge primarily in late summer and fall (August-October in northern regions). T. columba in New Brunswick shows peak oviposition from mid-August to mid-October. Some records suggest extended activity periods depending on latitude and climate.

Diet

Larvae feed on wood decayed by symbiotic fungus Cerrena unicolor, consuming both the fungal mycelium and the softened wood. feeding habits are poorly documented; may feed on tree sap or not at all.

Host Associations

Cerrena unicolor - symbiotic fungusRequired for larval development beyond first instar; females deposit fungus with . T. apicalis may lack mycangia and locate pre-infected wood using fungal volatiles.
Fagus grandifolia - oviposition Primary for T. columba in New Brunswick
Acer spp. - oviposition Maple favored by T. columba
Ulmus spp. - oviposition Elm acceptable for T. columba
Populus spp. - oviposition for T. fuscicornis
Salix spp. - oviposition for T. fuscicornis
Juglans spp. - oviposition for T. fuscicornis
Robinia spp. - oviposition for T. fuscicornis
Swida macrophylla - oviposition for T. apicalis in Japan
Pterocarya rhoifolia - oviposition for T. nakanei
Megarhyssa spp. - Giant ichneumon that parasitize larvae; three attack T. columba in New Brunswick
Ibalia spp. - Ibaliid wasps parasitize horntail larvae; I. japonica attracted to Cerrena unicolor volatiles

Life Cycle

Minimum two-year . laid in wood hatch in 2-4 weeks or the following spring. Larvae tunnel through fungus-infected wood, passing the second winter in larval stage. occurs within the tree, with emerging through exit holes. T. columba males emerge before females. Development time varies with and climate.

Behavior

Females use the ovipositor to drill into wood, bracing it at a 90° angle to the body and rhythmically thrusting it deep into solid wood. The process is lengthy and leaves the female vulnerable to . Males are often found resting quietly on foliage. T. apicalis females locate using volatile compounds from Cerrena unicolor rather than carrying fungus in mycangia. Emerging T. columba females may lay in existing galleries, producing all-male through .

Ecological Role

Primary decomposers of dead and dying hardwoods, accelerating wood decay through fungal inoculation. Serve as for including Megarhyssa and Ibalia . Important components of forest nutrient cycling, though occasionally considered pests when attacking stressed ornamental or fruit trees.

Human Relevance

Generally not considered pests as they attack already compromised trees. T. fuscicornis is an pest in Chile, declared mandatory control status in 2000. Non-venomous and harmless to humans despite intimidating appearance. Occasionally mistaken for dangerous stinging . Lumberjacks have given them colorful nicknames based on the appearance of oviposition .

Similar Taxa

UrocerusGiant wood wasps that attack conifers rather than hardwoods; generally larger and with different coloration
SirexSiricinae woodwasps that associate with Amylostereum fungus rather than Cerrena; some are serious forest pests
MegarhyssaGiant ichneumon that parasitize Tremex larvae; females have extremely long ovipositors but more slender bodies and different wing venation

Misconceptions

The prominent ovipositor is frequently mistaken for a stinger, leading to fear of these harmless insects. They cannot sting and are non-venomous. The cornus (short spur) is not a functional stinger either.

More Details

Fungal Associations

Tremex represents a distinct lineage within Siricidae through its association with Cerrena unicolor rather than Amylostereum. This relationship is obligate for most ; T. columba larvae cannot develop beyond first instar without the fungus. T. apicalis appears exceptional in lacking mycangia and locating pre-infected wood.

Parasitoid Complex

Tremex support diverse . Megarhyssa drill through wood to reach larvae, while Ibalia wasps attack more shallow larval stages. The parasitoids use fungal volatiles to locate , creating a tritrophic interaction network.

Invasive Potential

T. fuscicornis demonstrates capacity, establishing in Chile in 2000 and spreading in northern Germany. Its introduction prompted efforts using Megarhyssa praecellens. Most Tremex are not invasive and remain restricted to native ranges.