Grass-Carrying Wasp

2013 June 1

I found this blue wasp crawling on a window on July 5, 2012. It was pretty active, so I put it in the refrigerator so I could photograph it without its flying away. And, as it turns out, instead of just slowing down, it died. On the plus side, it died with its wings fully spread so we can see everything.

In wasps and bees, the ones with distinctly curly antennae tend to be the males, so I think this is a male wasp. And I was pretty sure it was one of the Thread-Waisted Wasps, family Sphecidae. I don’t think that there are any other wasp families that show that same kind of very elongated waist.

As for which species it was, my initial ideas were wrong[1]. It turned out to be a “Grass-Carrying Wasp” in the genus Isodontia, a type of wasp that I’d never heard of previously.

There are six species of Grass-Carrying Wasp, and two of them are completely blue-black like this but still have fairly pale wings: Isodontia apicalis and Isodontia mexicana. It could be either, as both species have been reported from around this area.

They are called “grass-carrying wasps” based on the way that the females build their nests. They are solitary wasps, and each wasp digs a burrow. She then collects blades of grass that she drags into the hole to build a lining for it. Once the hole is lined, she hunts for crickets, katydids, or similar Orthoptera, stings them to paralyze them, and drags them back to the hole. She then lays her eggs on the still-living (and therefore preserved) victims. These might be the wasps that I occasionally see dragging paralyzed grasshoppers across the road (but have never successfully photographed in the act).

If I’m right about this one being a male, he personally would have just flown around drinking nectar from flowers and looking for females.

[1] When I first found it, I thought it was a male Blue Mud Dauber, Chalybion californicum, and that it would be a companion post to the female Blue Mud Dauber that I posted back in 2009[2]. Except that it didn’t look quite right. In particular, the wings weren’t dark enough. I also thought it might have been a male Steel-Blue Cricket Hunter, Chlorion aerarium, which looks similar, but that one doesn’t seem to have such a fuzzy thorax, and also has darker wings. And both of them had the wrong pose. Thanks to bee and wasp expert John S. Ascher, it was finally correctly identified on BugGuide.

[2] Wow, I really need to re-shoot the pictures of the Blue Mud Dauber female from 2009. Those are terrible. They might be OK for general ID, but that’s about it.

3 Responses
  1. JRR permalink
    June 3, 2013

    “just flown around drinking nectar from flowers and looking for females.”

    Sounds like a good life 🙂

  2. Roma K. permalink
    November 16, 2013

    Very helpful article. I found one of these in my house and was afraid it was a termite queen or something. Thanks for the detailed photos and explanations!

  3. Grace Epstein permalink
    August 16, 2015

    Thanks for this posting. I am pretty sure this is the insect that has collected grass and little teeny green insects into the track that holds my window screens!

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