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In one of my earlier articles I wrote about the bronze birch borer. If you read the article you remember that we saw these insects that had bored themselves into the trunk of a stress birch tree. Researching what I thought was the birch borer, I wrote the article. I brought one of the insects to our last Master Gardener meeting and Peggy Boike did some further research on the insect. She contacted Jeff Hahn, Assistant Extension Entomologist at the University of Minnesota. Apparently what we thought was the bronze birch borer, has now been identified as the Horntail. This article is taken from information received from Jeff Hahn.

The order Hymenoptera is divided into two groups. The first group contains some of our most familiar insects, the bees, wasps, ants and parasitic wasps. The second group, known as the Symphyta, are the sawflies and wood wasps. Unlike bees, the wasps and ants, which vary in habits, the Symphyta are all plant eaters. Many of the larvae in this group are caterpillar-like.

One of the largest in this group are Horntails. They are stout-bodied insects, measuring from one to two inches long. They get their name from a horn-like projection extending back from the abdomen. On males it is short while it is longer and somewhat spear-like on the females. Horntails lay eggs in deciduous trees and conifers that are either dead or in a greatly weakened condition. The eggs hatch into whitish, legless, cylindrically-shaped, worm-like larvae. They bore into the trunk and large branches, creating meandering tunnels in the sapwood and heartwood. Larvae eventually pupate in these galleries and emerge as adults, chewing a hole through the wood to escape. Because they rarely attack healthy trees, horntails are not considered a pest in the landscape.

The most common horntail is the pigeon tremex, Tremex columba. It is also the largest horntail in Minnesota, with females measuring two inches long. The pigeon tremex has a reddish brown head, a reddish brown and black thorax, and a black abdomen with yellowish stripes. It also has long, amber-colored wings. This horntail prefers maple but also commonly attacks many other deciduous trees, including oak, elm, hickory, apple, and birch. Adults are most active during August and September.

Because they are not attacking healthy trees, no treatment is needed.

Horntails may also be brought indoors in infested firewood or wood used in construction. Fortunately, they do not infest any wood found indoors and would die on their own in a few days. Despite their size and the ominous look, horntails do not sting and are harmless to people. No control is necessary for horntails found indoors except for physical removal.

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