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Dianthidium bees make masons look like amateurs

Although they are not generally known as mason bees, the members of the genus Dianthidium certainly outshine Osmia bees when it comes to actually building something. Dianthidium bees collect pebbles, stones, and gravel, then cement them together to form a structure that can be pounded by the elements. The resulting nests are both impressive and beautiful.

This past summer I was fortunate to find several Dianthidium bees at the home of Larry and Naomi Price in Prineville, Oregon. They have a sweet little patch of Grindelia (curly-cup gumweed) alongside a gravel road. The patch attracts the most amazing collection of native bees I have ever seen. Among the blooms, I found some colorful Dianthidium bees back in July.

Another member of the Megachilidae

As you might guess, Dianthidium are related to Anthidium in the family Megachilidae. The name means “another Anthidium,” signifying their close relationship and many similarities. But while most Anthidium species nest in pre-existing cavities, some (but not all) of the Dianthidium build from scratch.

The ones that build choose a rock, a twig, or even an exposed root in an underground cavity, and begin by gluing a foundation layer onto the chosen surface. They collect pebbles, tiny stones, and “rocklets” to build with, and cement them together with plant resins and chewed leaves. Then they collect tiny particles—sand or soil—to use like grout wherever reinforcement is needed.

A completed stone hut

The pebble nest shown at the bottom of the page was photographed in Arizona by Patti Zigler. Bear in mind that the bees in my photo are not necessarily the same species of Dianthidium as the ones that built the nest. Nevertheless, it will give you a very good idea of what these bees look like and what they can do.

As you can see, the exposed nest is built on a tree branch. The entrance hole is at the bottom so precipitation does not drip onto the brood. Although these bees are found across the United States and into Canada and Mexico, the ones that build nests like this are most likely to be found in drier areas where there is limited rainfall to erode the structure. When I look closely at the rocklets, it seems improbable that a little bee about 5–12 mm long could collect them. Bees are truly amazing.

One waspy-looking bee

Like all bees in the Megachilidae family, Dianthidium carry pollen in an abdominal scopa which you can see in the first photo. The integument of these bees is usually black with contrasty yellow markings, making them look especially wasplike. They are solitary bees that forage on many plants, but they have a preference for those in the Asteraceae family, like the Grindelia shown below.

Grindelia offers a rich source of nectar and pollen, but it also offers plant resins which can be used as glue and waterproofing. In fact, after touching these plants, my hands smell strongly of turpentine—or something similar—for hours afterwards.

Keys to identity

For those of you who like to identify bees, Dianthidium have a pronotal lobe that is translucent rather than opaque, they have a mid-tibial spine on the hind leg, and they have an arolium between the tarsal claws that Anthidium are lacking.

I extend a special thanks to Patti Zigler for finding, photographing, and posting the pebble nest.

Rusty
Honey Bee Suite

Dianthidium bees have a wasp-like appearance, due to the strong yellow and black markings.
Dianthidium bees have a wasp-like appearance due to strong yellow and black markings. © Rusty Burlew.
Bees of all sorts love gumweed flowers (<em>Grindelia</em>). Here you can barely see the bee's pollen-covered abdominal scopa and a spine on the tibia of the hind leg.
Bees of all sorts love gumweed flowers (Grindelia). Here you can barely see the bee’s pollen-covered abdominal scopa and a spine on the tibia of the hind leg. © Rusty Burlew.
A view from the rear showing markings that look very similar to Anthidium bees.
A view from the rear showing markings that look very similar to Anthidium bees. © Rusty Burlew.
I would love to know if this particular bee has a stone hut. Since she is living in a desert environment, there is a good chance of it.
I would love to know if this particular bee has a stone hut. Since she is living in a desert environment, there is a good chance of it. © Rusty Burlew.
This amazing Dianthidium nest was found by Patti Zigler on December 10, 2018 at the McDowell Sonoran Preserve, Maricopa County, Arizona. Photo © Patti Zigler. CC License.

Comments

Alice
Reply

Fascinating. I would have never imagined a bee would build a stone nest. Honey bees struggle sometimes to carry off dead bees, how could such a tiny bee pick up a stone or rocklet?

The nest in the photo…about how big is it? I don’t think I’d find them here in SW Ohio (too wet), but are they very noticeable or so small one doesn’t always notice their presence?

I always learn something from your blog, Rusty, and you make learning fun. Well done!

Rusty
Reply

Alice,

I don’t know how big the nest was. I’ve been trying to contact the photographer, but she hasn’t yet answered. Perhaps after the holidays I will be able to track her down and ask that question, which is the same one I had.

Rebekah Lee
Reply

How far north in WA does this species exist?

Rusty
Reply

Rebekah,

I don’t even know which species this is, but the genus Dianthidium is fairly large with 23 species in North America. They appear across North American from southern Canada to Costa Rica.

Glen Buschmann
Reply

Thanks for another great story and superb photos. Ain’t life grand. In defense of Osmia, (who admittedly have an excess of defenders), I have several times found columns of mason bee mud chambers tucked into dry dark corners. I’ll email you a photo. But the mud and grit creations are fabulous.

While mud structures might seem better suited to dry conditions, evidence challenges this limitation. I’ve found solitary little sealed mud pots about the size of a large blueberry freestanding on a plant stem, in rainy Olympia. (I assume that these are wasps, but not pursued it further, simply admired the work.) We know that many bees excrete waterproof sacks and plasters. Many of the Chalicodoma bee species that Fabre wrote of assemble nests from grit and little pebbles, and some Osmia do too. Beyond Hymenoptera, consider lowly barnacles that anchor themselves to anything wet or dry, or caddis flies who glue together a great diversity of pebbles and twigs for under-water living. Why wouldn’t bees have access to the same tools in natures wonderful biological laboratory, wet and dry?

Thanks, Glen

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