European Wood Wasp (Sirex Woodwasp)

Sirex noctilio


Photo of male and female European wood wasps on pine stump
Vicky Klasmer, Instituto Nacional de Tecnologia Agropecuaria,

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


Wood wasps, or horntails, as a group are large, robust and wasplike but do not have a constricted "waist" behind their wings like other wasps; also, they have a spear-shaped spine at their "tail end," which gave them the “horntail” name. Adult European wood wasps are metallic bluish-black with reddish-yellow legs, black feet and black antennae. Males have an orange band around the abdomen and black hind legs. Females, in addition to the “horntail,” also have a stout, long ovipositor for inserting eggs into wood.

Larvae are creamy white, legless, with a dark spine at the hind end, and thus look very much like the larvae of our native horntail species. When new adults emerge from tree trunks, they create round exit holes about 1/8 to 3/8 inch in diameter.


Length: 1 to 1 1/2 inches.


Photo of European wood wasp larva in gallery in pine wood
European Wood Wasp Larva


Photo of European wood wasp female emerging from wood
European Wood Wasp (Emerging Female)
Habitat and conservation

European wood wasps have been arriving in our country inside wooden crating and other cargo materials. Fortunately, many are detected in time, but the insect has been found in New York state, away from ports. In its native range (Eurasia and northern Africa) it is a minor pest, but in countries where it is introduced, it becomes a serious pest of many species of pines. It is not yet widespread in our country. For the sake of our forests, learn to spot this exotic insect and its signs.


European wood wasps depend on pine trees for their life cycle. As the females insert their eggs into the outer sapwood of the tree, they simultaneously inject a symbiotic fungus and a mucus that cause the tree tissues to deteriorate; the larvae of the wood wasps feed on the fungus as they tunnel through the wood. Unfortunately, the fungus and mucus end up killing the tree entirely. Where European wood wasps have been introduced, they can cause up to 80 percent tree mortality.

image of European Wood Wasp Sirex Woodwasp Distribution Map
Distribution in Missouri

Not yet discovered in Missouri, but potentially statewide (anywhere there are pine trees).


Extremely destructive, invasive, non-native species. It poses a significant threat to many species of pines, and therefore threatens natural ecosystems as well as agricultural and horticultural interests.

Life cycle

In our area, new adults would probably emerge from tree trunks July through September. After mating, female wasps insert 25-450 eggs into the tree trunk, along with the fungus and mucus that eventually cause the tree to die. Unfertilized eggs develop into males, and fertilized eggs produce females. For 10-11 months, the larvae develop inside the tree, eating the fungus, which has rendered the fibrous wood into a digestible form. Pupation takes about 3 weeks; then the adults emerge.

Human connections

This and other exotic pests are arriving in countries where they don’t belong as a result of global shipping. The USDA works hard to inspect new cargoes--for example, for wood with holes leaking sawdust--which protects not only agricultural interests, but our natural ecosystems, too.

Ecosystem connections

This insect causes significant mortality of several species of pines, whether they are in backyards, Christmas tree farms or wild places throughout the country. If 80 percent of the pines in a pine forest die, it would devastate the community of animals and plants that live in that forest.