I am constantly surprised. I am also fortunate to have an extra set of keen eyes whenever my wife and I go exploring together. The evening of June 9 we decided to enjoy Sinton Pond Open Space here in Colorado Springs. While trying to get a picture of a damselfly, Heidi spied something even more interesting: a sleeping wasp in the family Ibaliidae.
I know, I’d never heard of them, either, at least until I found a specimen in Cincinnati when I lived there. I tried to turn it into some kind of ichneumon wasp, but it simply didn’t fit any of the characters for Ichneumonidae. I don’t recall how I finally found the answer, but I was certainly shocked to learn its nearest relatives are gall wasps.
There is one genus, Ibalia, in North America, with six species, the most widespread of which appears to be Ibalia anceps. Its distribution extends from Nova Scotia, Ontario, and Wisconsin south to Florida and Texas and west to Colorado. Geographic variation accounts for different color patterns in the wings. Ibalia anceps adults fly mostly in late May and early June.
Ibalia are parasites of horntail woodwasps in the family Siricidae. The female wasp lays an egg on the horntail grub, which is inside a dead, dying, or weakened deciduous tree, such as hickory. The larva that hatches from the ibaliid egg then penetrates the cuticle of the horntail larva and begins feeding as an internal parasite. Later, as the larva grows, it exits the host and finishes feeding as an external parasite.
Here locally, the only common horntail is the Pigeon Tremex, Tremex columba, so that must be the host. Indeed, elsewhere across its range, I. anceps is associated most often with T. columba. Please see my post on the Pigeon Tremex for more information about that wasp.
Ibaliids may be recognized by the laterally compressed abdomen. The abdomen is so thin that it conveys the impression that the rear end of the insect was smashed between the pages of a heavy book. Male Ibalia have fifteen segments in each antenna, while females have only thirteen segments. Females also possess an ovipositor (egg-laying organ). Specimens average about 12-14 mm in length, which is gigantic compared to their tiny relatives in the superfamily Cynipoidea, most of which are around three millimeters.
Keep your eyes open for these unique wasps. Take images if you are able, and share them with other naturalists and entomologists.
Sources: Goulet, Henri and John T. Huber (eds.) 1993. Hymenoptera of the World: An identification guide to families. Ottawa: Agriculture Canada. 668 pp.
Nendick-Mason, Hannah, et al. 2006. “Species Ibalia anceps,” Bugguide.net.
Smith, David R. and Nathan M. Schiff. 2002. “A review of the siricid woodwasps and their ibaliid parasitoids (Hymenoptera: Siricidae, Ibaliidae) in the eastern United States, with emphasis on the mid-Atlantic region,” Proc. Entomol. Soc. Wash. 104(1): 174-194.