Sirex noctilio - Midnight Woodwasp

Widespread throughout Britain north to Perthshire with a clear uptick in records in recent years. Scottish records, albeit these are very sparse, should perhaps be checked against the potential for atricornis (Musgrove, 2022).

The female is black bodied. The venation is more brownish than the male and the wing usually has weakly brown banding apically and through cell 1R1. The sawsheath is shorter than the oblong ventral plate from which it arises. The ovipositor has large pits along its length separated from each other by their own length at the mid-point.

The male is similar but with a red band on the middle tergites. The ninth sternite is deeply and acutely incised. Male wing venation is usually yellow and the wings are not conspicuously banded.

In both sexes, vein Cu1 is incomplete (present only as a stub). The mesopleura are densely punctured with the spaces between, smaller than the punctures. In certain light the mesopleura and abdominal tergites are iridescent violet. The legs are mostly reddish-yellow, and the femora can vary from black to reddish-yellow. The apical tarsal segment is dark in contrast to the preceeding segment.

Females live for about 3 weeks and once they have mated, they look for weak and stressed pine trees to lay their eggs in. A female can lay several hundred eggs. Using their tough, needle-like ovipositor they drill into the heartwood of the selected tree. The ovipositor is strengthened by having zinc within the outer layer. Having drilled into the tree the female then inserts a mixture of toxics, to further weaken the tree, and fungal spores (Amylostereum areolatum) that grow and feed on the wood fibres. It is the fungus and rotting wood that the larvae then feed on. It can take up to three years for the larvae to grow and the emerging new adult females will collect some of the fungal spores into special glands prior to flying off to start the next generation. Emergence is triggered by a reduction in the differential temperature between day and night.

Sirex noctilio larvae are parasitised by the wasps Ibalia leucospoides and Rhyssa persuasoria.

Jump to other Sirex species

Size: 14 - 35mm

GB IUCN Status: Least Concern
GB Rarity Status: None

Distribution: England, Scotland, Wales, Ireland

Flight period: July to October

Plant associations: Piceae spp. including Pinus spp. (pines), Picea spp. (spruces), Abies spp. (firs), Pseudotsuga spp. (firs), Larix spp. (larches), Picea abies (Norway spruce), Pinus sylvestris (Scots Pine). Pines are preferred.


Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London

Chrystal, R.N., 1930. Studies of the Sirex Parasites. The Biology and post-embryonic Development of Ibalia leucospoides Hochenw.(Hymenoptera-Cynipoidea). Clarendon Press, Oxford.

Liston A, Knight G, Sheppard D, Broad G, Livermore L (2014) Checklist of British and Irish Hymenoptera - Sawflies, ‘Symphyta’. Biodiversity Data Journal 2: e1168.

Liston, A. D. 1995: Compendium of European Sawflies. List of species, modern nomenclature, distribution, foodplants, identification literature. - Gottfrieding, Chalastos Forestry : 1-190

Musgrove, A.J. 2022. A review of the status of sawflies of Great Britain - Phase 1: families other than Tenthredinidae. Natural England, unpublished

Schiff, N. M., Valley, S. A., LaBonte, J. R. and Smith, D. R. (2006) 'Guide to the siricid woodwasps of North America.' Forest Service, Forest Health Technology Enterprise Team. USDA, Morgantown

Viitasaari, M. & Midtgaard, F. 1989: A contribution to the taxonomy of horntails with notes on the genus Sirex Linnaeus (Hymenoptera, Siricidae). - Annales Entomologici Fennici, Helsinki 55(3): 103-110