There are some fascinating and peculiar insects under the big tent of wasps and the smaller umbrella called Symphyta, the sawflies and parasitic woodwasps. Today, you’ll meet a woodwasp in the genus Orussus.
Even though some of the information I’ve read online says woodwasps are rare, I’ve seen them twice at Mount Pisgah, most recently in late October. In both cases, they were moving oddly on a human-altered piece of wood, either sidling sideways or tapping the wood, and sometimes lifting up a back leg at an awkward angle.
Orussus are ectoparasites, which means their larvae latch themselves to the outside of a host, and feed on it as the woodwasp grows to the next stage. This woodwasp parasitizes wood-boring, aka Buprestid, beetle larvae.
Females find the host larvae with their antennae, using echolocation on fir trees. They don’t patrol trees with thick bark, but test out dry and bark-less wood.
Orussus have a couple of identifiers to help discern them from wasps. Their antennae originate low on the face, below the eyes, and their wings have fewer veins than most wasps. There are only 28 species known in the world, five or six in North America, and two in the Pacific Northwest.
Females have extremely long ovipositors, longer than their body length, but you can’t tell a male from a female unless you find one laying eggs. That’s because until it’s needed, the females keep the long egg-laying wand inside their abdomen, sometimes coiled up!
See more of Karen’s work here.
Olympic Peninsula spottings: https://onh.eugraph.com/insects/hymenop/orussus/index.html. Accessed 11/7/23.
Orussus info on SawflyGenUS: https://idtools.org/sawfly/index.cfm?packageID=87&entityID=742. Accessed 11/7/23.
1975 paper on oviposition: https://www.jstor.org/stable/25082758. Accessed 11/7/23.