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Close in — tiny mud pot forms on wall

Every once in a while, I find a clay pot — a tiny, perfect clay pot — on the wall of the house.  They look like little half-buried Mediterranean amphorae, without handles, with a narrow neck and a flared rim, the entire thing only half an inch across.  But they have no openings: like the false-necked vessels drachmai-conscious Athenian families left at the graves of loved ones — they looked full of precious oil while only actually containing a thimbleful — these tiny pots are sealed at the top.  Sometimes, however, they have a hole in the side, as if a micro-tomb-robber struck the belly of the pot with a spade, to sift through the contents.

A little spadework in books and on the internet turned up the answer to who the tiny potters in our yard might be : Microdynerus arenicolus, the Antioch Potter Wasp, who builds up this mud cell for its offspring one mouthful of clay at a time.

You would think a wasp bringing mouthful after mouthful of mud to a wall right by the front door might be observed easily, but I’ve never knowingly seen one of these wasps on the job.  What I can glean about the appearance and habits of the Antioch Potter Wasp is that they are about half-an-inch long, live in California, southern Arizona and New Mexico, and are solitary wasps.  The adults have creamy white or yellow and black markings, and there are subtle differences in coloring and morphology between males and females that are probably mostly important to other wasps and entomologists.  (The photo on the left is not our Potter Wasp, it’s a related species from Australia.)  The females have stingers, but are “docile”.  They are also “domestic”: it’s the female who does all the housework.  Here’s what an Arizona Game and Fish document says about the Antioch Potter Wasp:

These are solitary wasps, each female constructing nests and provisioning them for her own offspring. Each nest looks like a small jug, about half an inch in diameter, with a short sealed neck. When the female decides to make a cell, she selects a sheltered place, and then carries dollops of mud there for construction. This is a precision process with a thin walled pot resulting. When the pot is almost completed, with just room for her to get her head in, she starts to provision the cell with hairless caterpillars, which she has paralyzed by stinging them in the central nervous system. Once the cell is full she lays an egg on the prey and restarts the cell making process. She adds mud to the edges of the nearly spherical pot. Closing the sphere presents problems that are solved by simply adding extra mud and leaving a small neck. The larva that hatches from the egg eats the prey, spins a cocoon inside the pot and pupates. When the new adult is ready to leave the pot, it simply makes a hole in the side and leaves. Using the neck would be logical but that is where the pot is the thickest.

–Arizona Game and Fish Department. 2004. Microdynerus arenicolus. Unpublished abstract compiled and edited by the Heritage Data Management System, Arizona Game and Fish Department, Phoenix, AZ. 4 pp.

Unless you’re a hairless caterpillar, this is a fascinating process.  Especially for a potter: the technique of building a pot from the bottom up, adding little bits of clay at a time, and contouring it as you go is exactly the technique potters use to build vessels or vessel-like sculptures.  Vessels of any size and shape can be made as long as the supply of moist clay holds out: the potter wasp makes her own by carrying a mouthful of water to a dry clay source and mixing it up to the right consistency and carrying it to the construction site.  To the right is a picture of a Three Star Owl VLO (Very Large Owl) being constructed in the same way as a potter wasp builds her nest.  (It will be more than two feet tall and at this point lacked its face.  Please note that the finished owl sculpture was not provisioned with hairless caterpillars nor were any eggs at all laid during the process.)

I determined to keep an eye on the little wasp-pot, hoping to see a new wasp break free and fly away, to carry on the work of potter wasps in the yard.  Of course, the next time I looked, there was the hole, and the empty belly of the tiny clay amphora — the wasp had flown.  Here’s a picture of the hole made from the inside out by the wasp itself, not a grave robber after all:

Etymology

The common name, Antioch Potter Wasp, seems like a very appropriately Mediterranean name for an organism that makes structures that look like amphorae, the storage and shipping vessels found all over the Mediterranean region from about the 13th century BC until the 7th century AD.  But it’s mere coincidence, and not connected with the ancient city of Antioch on the Levantine coast of the Mediterranean (the stretch of land from which the earliest amphorae, the so-called “Canaanite jars”, come), a hub of commerce and shipping.  The species was given its name from the town of Antioch, California, also a hub of commerce and shipping, where the type specimen was collected and described.

(Photos: #1, 3, 4, A.Shock, Three Star Owl.  #2, from the following site: http://www.geocities.com/brisbane_wasps/images/MudDau7.jpg, no photo credit found)

Posted by Allison on Dec 8th 2008 09:45 pm | 8 Comments
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8 Responses to “Close in — tiny mud pot forms on wall”

  1. Veronicaon 06 Sep 2010 at 5:19 pm link comment

    I live in Upstate NY near Buffalo and while sweeping my porch, I noticed a strange little mud pot stuck between the cushion and the back of one of my porch chairs. Thanks for solving my little mystery! I have seen them in action on my back deck with the little green worms, but they were going into a hole in a deck light with the prey.

  2. Allisonon 06 Sep 2010 at 7:57 pm link comment

    Veronica, my husband told me just yesterday he saw a wasp predate a little green “inchworm” in mid-air, from the end of the small worm’s silk cord as it hung from a palo verde tree. It didn’t occur to me until I read your comment that instead of a predatory wasp capturing lunch for itself, it could have been one of our female potter wasps provisioning a “pot” nest for her larva. So, thanks right back to you, as well!

  3. Samanthaon 25 Sep 2010 at 4:17 pm link comment

    I live in Pensacola, Florida and I found a little terra cotta pot stuck to one of my socks hanging outside to dry. I was amazed because normally the only thing that gets on clothes is from pesky birds, if you get my drift. This was hollow and looked like it was made from a living creature. I was so amazed that I took 3 photos to show people, and then being afraid it might be a spider’s nest I crushed it on the sidewalk. It sounded like a piece of ceramic breaking. Wow. It really was a terra cotta pot created by something. So I looked it up and I found this. Do you think those wasps live in Florida?

  4. Allisonon 25 Sep 2010 at 5:51 pm link comment

    Samantha, I think there are Potter’s wasps (Eumenes spp) where you live. Here’s a link to an informational site specifically about Florida’s potter’s wasps: http://entnemdept.ufl.edu/creatures/misc/wasps/potter_wasps.htm
    By the way, I also dry my laundry outside on a line, so I know all about birds and clean clothes! Although, I must say, it happens less often than you’d think… I’ve never had a potter’s wasp build a nest on my drying clothes, though!

  5. Samanthaon 25 Sep 2010 at 6:40 pm link comment

    Thanks for the link. I feel kind of bad for smushing it. It sounded like I was crushing glass. I don’t mind bees as much as I do spiders. I take a lot of bumblebee photography for my art work. Since I don’t have children yet I don’t have to worry about bee stings. Anyways, thanks for letting me know.

  6. [...] of an un-opened Potter Wasp nest on the front wall of our house, with a drawing pencil for scale.  Click here for more info on what these tiny clay pots are, and why the wasps build them.  One of these days, I hope to be [...]

  7. Paton 18 Jul 2012 at 10:07 pm link comment

    I found one of these pots on my doorstep today in Seattle, WA. It had three little green inch worms in it that were still alive but would only twitch when disturbed. At first I figured the pot was a wasp nest but the inch worms inside really threw me off. Glad I found this site that so eloquently explained what I found. Thanks!

  8. Allisonon 19 Jul 2012 at 6:39 am link comment

    Pat, glad you found useful info here. I don’t know if your Seattle potters are the same species, but types of potter wasps do seem to live all over the country, and the world. “Our” potter wasps have been very active this summer here in our yard. I’ve finally seen several, catching one in the process of building a little pot on the leaf of a Hoya in a planter hanging on the back porch: they’re brown and yellow and have a very slender, double-jointed looking abdomen. This nest was broken into by a predator — probably a Cactus wren — but I recently found another successful pottery nest near the first, with the single small-bore hole in the side made by the emerging new wasp. I still haven’t been able to capture an emergence on camera, though — or even an adult wasp, though!

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