Horntails

About 28 species in North America

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Photo of a Pigeon Tremex Horntail
The pigeon tremex (Tremex columba) is a common horntail species. Like other horntails, it is wasplike, but with a taillike spine that projects from the tip of the abdomen.
Donna Brunet
Other Common Name
Wood Wasps
Family

Siricidae (horntails) in the order Hymenoptera (ants, bees, wasps)

Description

Horntails are wasplike insects with a taillike spine that projects from the tip of the abdomen. They have cylindrical bodies and lack the narrow waist so common in wasps. They are usually black or brown, sometimes with rust, orange, or yellow markings. Some species are fairly large. Males and females both have a hornlike spine at the abdomen tip; females have an additional projection below, which is the ovipositor, used for laying eggs.

Horntails do not sting or bite.

Larvae are pale yellow or white segmented grubs with 6 tiny legs. They are rarely seen because they bore in the wood of trees.

A number of species might possibly be found in Missouri.

  • The pigeon tremex, or pigeon horntail (Tremex columba) is variable in coloration, ranging from dark to light brown, often with yellow bands on the abdomen and dark or amber-colored wings. Antennae are brown and relatively short and blunt. This horntail can be 2 inches long. Because it is one of the few horntails that prefers deciduous trees, and not conifers, and because Missouri's forests are mostly of deciduous trees, this is the horntail most commonly encountered in our state.
  • Urocerus taxodii has yellow-tipped antennae and a pale spot on each side of the head. Females are black or dark-bodied with dark wings and a yellowish horntail. Males are orange- or yellowish-bodied with paler to clear wings. This species lives on bald cypress trees, which is common in southeast Missouri and planted statewide.
  • Urocerus albicornis is a black horntail with 2 white or yellowish bands on each leg, white or yellowish antennae with black tips and bases, a white or yellow spot on either side of the head, and brown wings. It sticks to areas with conifers (pines, cedars, and so on).
  • The sirex woodwasp or European woodwasp (Sirex noctilio) is an invasive nonnative species that could potentially be found in our state. This species is known to cause the death of up to 80 percent of the pine trees in an area, and Missourians should be on the watch for it. Adults have metallic bluish-black bodies with reddish-yellow legs, black feet, and black antennae. Males have an orange band round the abdomen and black hind legs.
  • The Asian horntail (Eriotremex formosanus) is native to southeast Asia and has been accidentally introduced to North America in shipping crates or other imported wood products. On our continent, it mainly is known from US southeastern coastal areas ranging from Texas to Florida to Virginia, though it has been found in Utah and Arizona. It could potentially occur anyplace that receives shipments from overseas. Fortunately, its larvae mainly eat dead wood or wood from dying trees, so it is not a serious pest or threat to our forests. It is a dark brown and yellow-striped wasp with short, black, blunt antennae and long yellow hairs on the top side of the abdomen. It could potentially appear in our state.
Size

Length: ½ to 2 inches (varies with species).

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Photo of male and female European wood wasps on pine stump
European Wood Wasp (Sirex Woodwasp)
European wood wasp, female (left) and male (right). This species is known to cause the death of up to 80 percent of the pine trees in an area, and it could soon arrive in Missouri.

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Female pigeon tremex resting on a concrete surface
Pigeon Tremex Horntail
The pigeon tremex, or pigeon horntail (Tremex columba), has yellow and black bands on its abdomen and dark or amber-colored wings. It has a cylindrical, not narrow-waisted body. It can be 2 inches long.

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Pigeon tremex, closeup of head
Pigeon Tremex Head
As larvae, horntails chew wood. The powerful mandibles are visible on this closeup of a pigeon tremex's head.

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Female pigeon tremex horntail viewed from above
Pigeon Tremex Female
The pigeon tremex is the most commonly encountered horntail in Missouri. Only the females have the elongated horntail.
Habitat and conservation

Horntails may be found nearly anyplace with trees but are rarely numerous. Some species lay eggs in hardwood and others in coniferous trees. Historically, Missouri had large tracts of native shortleaf pine forest, but those are mostly gone today. Because most North American species of horntails require pines and other conifer trees, most North American horntail species occur in regions to our north, northeast, southeast, and west, where pine forests are common.

Missouri's most common species, the pigeon tremex, prefers maples, oaks, elms, sycamore, hickories, apple, pear, and hackberry. When laying eggs, horntails tend to select trees that are weakened or dying. The tunneling of the larvae can weaken wood, making it prone to further disease or damage. Sometimes they lay eggs on recently cut wood.

Foods

The young of horntails are wood borers, tunneling into the sapwood and heartwood of trees as they eat. Like several other insects that eat wood, larval horntails possess a symbiotic fungus that helps them digest the tough materials wood is made of.

image of Horntails Distribution Map
Distribution in Missouri

Statewide.

Status

Common.

Life cycle

After finding a host tree, the mother horntail uses her ovipositor to bore through the bark and inject eggs, one by one, as much as ¾ inch into a tree. After about a month, the eggs hatch into grublike larvae that eat wood, tunneling into the heartwood. They can grow for 1 to 3 years before pupating. Prior to pupation, they tunnel to just beneath the bark. When pupation is complete in late summer, they emerge as winged adults, chewing their way out of the bark, and repeat the cycle.

Human connections

Horntails usually do not occur in large enough numbers to be serious pests, though the boring of the larvae does damage trees. Typically, they select declining trees and not healthy ones.

Ecosystem connections

Like many other organisms that feed on dying trees, horntails help begin the process the recycles wood back into soil. Larval horntails are not safe in their tunnels; they are eaten by larval ichneumons, whose mothers also possess ovipositors for boring into wood.