As the nights cool and the leaves start to turn in the high country of Colorado, we find one of our Autumn bees laboring away. She’s collecting pollen to provision her nest, along with a smattering of sticks, stones, and resin that she’ll use in her elaborate, and highly variable nest plug. These “Resin with Debris” plugs that are now showing up across the Front Range foothills are the work of Dianthidium bee species.
In contrast to the narrow, black Aphid wasps (Passaloecus sp.) which also construct nest plugs from resin and top them off with scraps of whatever they find lying around, these artistic bees tend to nest in somewhat larger diameter tunnels (3/16″ – 5/16″ or the column 2 and lower column 3 holes in the 30 tunnel blocks) and use larger bits of debris and pebbles. They are, after all, larger and more robust insects! And rather than just topping off their resin plus with a layer of debris, the Dianthidium incorporate the debris into their nest plugs – almost using the resin as mortar.
Like their fuzz-loving cousins, the wool-carder bees (Anthidium sp.), Dianthidium superficially resemble yellowjackets, in that their integument (exoskeleton) is boldly marked with yellow and black. Unlike yellowjackets, these insects are solitary bees! Look for these bees on gumweed and asters.
We hope you have enjoyed this summer’s Plugs & Bugs series. Stay tuned for additional blog posts on a variety of subjects throughout the next few months.