![Figure 1: Orussus terminalis dorsal habitus](https://sites.psu.edu/frost/files/2020/11/Orussusterminalis1-300x225.jpg)
This week’s wasp is the parasitic sawfly species Orussus terminalis! This species. was first described by Edward Newman in the year 1838. Orussid sawflies represent an important part of the evolution of all wasps – read on to learn more about their critical place in the hymenopteran tree of life!
Taxonomy: This species is a member of the family Orussidae, which contains the parasitic sawflies. The family Orussidae contains around 85 living species in around 15 genera. Twelve species in three genera are known from North America. Most of these species are known from the south and west; only a couple are present in the northern and eastern parts of the continent.
![Figure 2: Orussus terminalis lateral habitus](https://sites.psu.edu/frost/files/2020/11/Orussus_terminalis2-300x225.jpg)
Identification: A sawfly (a member of “Symphyta”) is identified primarily by the lack of a distinct constriction between the thorax and abdomen. The family Orussidae is identified by the presence of distinct thorn-like projections on the top of the head between the eyes, in addition to the antennae, which are inserted low on the face near the upper border of the mouth. The genus Orussus can be diagnosed by the presence of significant white markings on the legs, in addition to a lack of longitudinal ridges on the head.
![Figure 3: Orussus terminalis, three-quarters view](https://sites.psu.edu/frost/files/2020/11/Orussus_terminalis3-300x225.jpg)
Natural History: Other sawflies, known under the defunct suborder “Symphyta,” are all plant-feeding, but members of Orussidae are all true insect parasitoids. In fact, this family represents the origin of parasitism in the order Hymenoptera. This lifestyle, along with a handful of other factors, is responsible for the explosion of diversity experienced by the order. As a result, the family Orussidae may prove to be the most important hymenopteran family for understanding the overall evolutionary history of the group. The incredible diversity of the parasitic Hymenoptera is often cited as a reason for Hymenoptera potentially unseating Coleoptera as the most speciose insect order, although many discoveries need to be made to substantiate this idea. Members of the family Orussidae themselves target bark-dwelling insects, including members of Buprestidae, Cerambycidae, Siricidae, and Xiphydriidae. To add to the craziness, female orussids use echolocation to find hosts underneath tree bark – this strategy is present in a number of parasitic wasp groups, but is impressive nevertheless!
![Figure 4: Orussus terminalis anterior view](https://sites.psu.edu/frost/files/2020/11/Orussus_terminalis4-300x225.jpg)
View This Species On:
BugGuide: https://bugguide.net/node/view/205363
iNaturalist: https://www.inaturalist.org/taxa/495064-Orussus-terminalis
References:
- Aguiar, A. P., Deans, A. R., Engel, M. S., Forshage, M., Huber, J. T., Jennings, J. T., … & Miko, I. (2013). Order Hymenoptera. In: Zhang, Z.-Q.(Ed.) Animal Biodiversity:An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013). Zootaxa, 3703(1), 51-62.
- Goulet, H., Huber, J. T. (1993). Hymenoptera of the world: An identification guide to families. Ottawa: Research Branch Agriculture Canada.
- Vilhelmsen, L., Blank, S. M., Liu, Z., & Smith, D. R. (2014). Discovery of new species confirms Oriental origin of Orussus Latreille (Hymenoptera: Orussidae). Insect Systematics & Evolution, 45(1), 51-91.