Tremex – Tremex columba – Siricides

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The tremex looks like an elongated, cylindrical wasp . Its thorax is reddish-brown and its abdomen has yellow and black stripes. The coloring of the wings varies from amber brown to black. Adults of both sexes have sharp appendages at the end of the abdomen. The female also has a slender, elongated egg-laying organ called an ovipositor. The adult insect is between 2.5 and 5 cm long, the female being a little larger than the male.

The white larva has a light brown head and a black thorn at the end of the abdomen. Its legs are poorly developed. It reaches 5 cm long.

Life cycle

After mating, the female lays eggs in weakened or dead trees. She uses her ovipositor to deposit her eggs under the bark. This egg-laying organ sometimes gets stuck in the tree causing the death of the female trapped on the trunk.

During the laying, a fungus is also introduced into the wood. The presence of this fungus, Cerrena unicolor , is necessary for the full development of tremex. It is said that this fungus and tremex live in symbiosis, since their association is beneficial to both species.

The larvae dig long galleries in the wood to feed. As there are no holes to expel the sawdust, it accumulates in the galleries. The tremex spends about a year as a larva, then three to five weeks as a pupa. It then transforms into an adult, who cuts a perfectly round exit hole in the bark measuring 3 mm in diameter.

In total, the life cycle of tremex usually lasts 2 years.

Geographical distribution

This species is found in southern Canada in most provinces, as well as in several US states.

Host plants

The female lays eggs in the wood of several species of deciduous trees (beech, maple, elm, walnut, oak, apple, pear, etc.).


The tremex larva feeds on the wood of several deciduous tree species that serves as host plants. It also feeds on a microscopic fungus, C. unicolor , which the female introduces into the tree when laying eggs.

What you need to know

Reaching 5 cm in length, not counting the ovipositor, the tremex is the largest of the Hymenoptera .

This insect does not sting or bite.

Tremex larvae are often parasitized by Black Rhysse , an insect of the ichneumonid family. The female rhysse has a very long ovipositor. Able to detect the presence of tremex larvae under the bark, it pierces the wood to lay its eggs on its host. After hatching, the rhysis larva feeds on the tremex larva, causing its death.

Ecological roles

Although the larvae of this species feed on wood, the host trees are usually already depleted. According to some authors, the presence of this insect has little effect on tree health. Others consider T. columba to be a forest pest of notable importance.

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