Sirex is a genus of wasps in the family Siricidae, the horntails or wood wasps. They inject eggs with fungal endosymbionts into wood. The fungus is contained in a mycangium which nourishes it with secretions, and in turn it digests wood for the wasp larva. The genus includes economically important pests; S. noctilio, known simply as the 'Sirex woodwasp' is an invasive species, having spread widely across the world from its original range.