by Sandy Garland

Grass-carrying wasps (Isodontia mexicana) use hollow stems or tunnels in wood to build nests for their offspring

I love this species because it’s so easy to identify, especially if it’s building a nest. I was watching the insect hotel at the Fletcher Wildlife Garden one day and noticed that several “rooms” were stuffed with bundles of grass.

“Who would do that?” I exclaimed and bent down for a closer look thinking that vandals had plugged up potential nest holes. I was about to pull out the grass stems when a wasp flew over my shoulder and proceeded to poke another blade of grass into the hole.

I was astonished. I hurried home and Googled “wasp carrying grass.” More astonishment – and some laughter – when the search engine came up with “Grass-carrying Wasp (Isodontia mexicana).”

We are trying to find out as much as we can about all our local pollinators, and, as this one is now dear to my heart, I Googled its name recently and found a wonderful article by Heather Holm, containing just about everything I wanted to know about this creature: Meet the Grass-Carrying Wasp, a Gentle Pollinator of Summer Flowers.

Parchment-lined tunnel in wood has been used by a Grass-carrying Wasp

I learned that it IS a pollinator. Even though it gathers dead insects, not pollen, for its offspring, the adults visit flowers to feed on nectar and, in doing so, incidentally carry pollen from one plant to the next. And I learned that the cocoons I have in my refrigerator are likely a second generation of larvae and they will emerge in early summer – lots of time for me to get them back outside where they’ll find the resources they’ll need as adults.

Heather’s article mentions the kinds of wildflowers these wasps prefer, what sorts of nesting sites they use, and other interesting facts about the various stages of their life cycle. I enjoyed seeing the many photos she included, especially the ones showing the inside of a nest tunnel. At the FWG, we have not observed them using plant stems or the rolled paper tunnels we make for Mason Bees. But we do see them using holes in wood quite regularly. (Note: we line these holes with parchment, which can be replaced, making them easy to clean.)

Please let us know if you see these wasps in your backyard. By all accounts, they are NOT aggressive, so welcome them as another member of our local pollinator “team.”

One more thing: Grass-carrying wasps will nest in any small hole, so people often find bundles of grass wedged into spaces around window frames. This is NOT a reason for concern and the wasps know what they are doing, so please be content to share the space until the adults emerge in early summer.

Other articles on the Grass-carrying Wasp

12 Responses to “Grass-carrying Wasp (Isodontia mexicana)”

  1. Elaine Wilkinson McKean says:

    Thanks for posting this, and with a great picture, too. I have had these wasps building nests in my wind chimes for a couple of years. The grass litter on my deck and the chime tube stuffed with trash was a mystery to me until yesterday when I observed not one, but two “ladies” struggling to gain height with dried grass blades many times longer than they. My light bulb finally went on when the wasps disappeared down the tunnel of the chime pulling the grass in afterward. So cool. I’m very happy for them to continue to do their thing. I live in Paris, Tennessee.

  2. Kelly Derby says:

    I have them nesting in patio chairs (of tubular structure with small holes on under side). I’ve never seen them before. Glad to learn more about them. I live in Lakewood, CO.

  3. Anne says:

    I just found a nest in one of my upper windows. Took me a while to figure it out. It looks as if the prey in the nest is still
    Alive and possibly paralyzed?
    We live in the Beaches, Toronto

  4. JRoberts says:

    I live in Clinton Arkansas foothills of the Ozark mountains this is the first year I have them stuffing blades of grass in the siding of my house . Glad to read they are not aggressive. I will leave them be and let them do there thing

  5. Laura J. says:

    I just found out about these wasps today. I saw dried grass sticking out of the bottom of one of my metal wind chime tubes. I pulled it out wondering what did this. Six green tree crickets fell out. I then Googled and the grass carrying wasp came up. Nature is so amazing, I learn from it every day!

  6. Lulu Anderson says:

    I have these little workers in the track of my window screen and in the bannister of my porch. Love watching them. Often carrying huge Tufts if dead grass or weeds…several inches bigger than them and carrying them down into the tracks or using the little nest hanger I have. I love how the weeds stick out of the bamboo “homes”.

  7. Brian Squibb says:

    Indeed, I have photographed many of these wasps on our Trumpet Vine in our backyard. Not aggressive at all in my experience (yet).

  8. Dexter smith says:

    I have one building a nest in my shelter house

  9. Violet Bevins says:

    First time I have seen the holes with grass poking out. We have lots of carpenter bee holes on our porch and have never seen this. Still haven’t seen the bees doing this. Have seen this in three different holes around the property. We live in Virginia

  10. PATRICIA A GRELA says:

    I’m in western, PA. I found a small pile of dead grass in my front porch watering can a few days ago. Didn’t think too much about it, just emptied the grass and went about my watering. Today, again I found grass in my can this time blocking the pouring tube. Brought it inside to clean out and found one wasp and about 20 barely alive small grasshoppers. Now that I know what’s happening, I will try to give the wasp an alternate location to nest.

  11. Diane Winters says:

    Hey neighbor, I live in Mountain View. Just a few miles away. A week or so I noticed blades of cut grass all over my porch, wrote it off to the wind knowing that probably wasn’t how it got there. This evening I saw a little sticking out the bottom of a tube on my wind chimes, which led me here. This is my learn something new today.

  12. Robin Rebold says:

    I live in Western Pa. and have a metal wind chime on my back deck. I noticed brown blades of grass and weeds laying on the deck in front of my chair that I sit in almost nightly. Much to my surprise I learned about these busy little creatures and welcome them to my yard.

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