Sirex cyaneus (Siricidae)

blue horntail (woodwasp)


Long cylindrical body about 20 mm long, thick waist, horn-like tail, two pairs of membranous wings unequal in size and shape, divided by longitudinal and cross veins into a few "cells."


Cylindrical grubs with pointed tail; head a hemispherical capular structure; thoracic legs rudimentary.


Grubholes in wood, circular in cross-section, filled with frass; exit holes from surface circular; wood may be stained by fungus which woodwasp plants in it. Adult female woodwasp bores hole into log with ovipositor and deposits an egg 15 mm or so in. Also, fungal spores, from pouch near ovipositor are deposited with eggs. Not yet clear if larvae feeds on fungus or wood pre-digested by fungus. Larvae remain in wood 1 or 2 years. Attacks freshly felled, fire killed or physiologically weakened trees.

Principal Hosts:

Abies lasiocarpa, Picea engelmannii, P. glauca, Pinus ponderosa and Pseudotsuga menziesii.

Economic Importance:

Larval mines degrade lumber cut from infested trees, but normally this becomes a problem only when lumber from burns or windthrows is marketed in large amounts.

References and Links:

EAG: 533-536; FC: 453-456.

Additional Images:

Sirex juvencus Urocerus albicornis