Mud Plugs (part 1) and their Bugs

Mud is used to plug the nests of many wasps and some bee species, including our earliest nesting bee, Osmia lignaria. Mud plugs are a complex set of plugs, with subtle differences that we are starting to understand. For this post, we focus on early season mud plugs. We will revisit mud plugs later in the season as additional wasps that also use mud begin nesting.

When reporting on mud plugs it is most helpful to us if you can include photos of the plugs and any insects you see entering, exiting, or plugging these nests. Adding comments about mud plugs such as the color (dark grey, tan, white, pale grey, reddish), texture (chunky, bumpy, smooth, grainy), and concavity (very concave, flat, bulbous) are most helpful, particularly if an insect was seen entering the nest. These, in combination with the date of observation, distance recessed or protruding, and intactness give us a more complete picture of what is happening. If you see the insect, but can’t photograph it, comments including the color and shape (round blue bee, skinny black wasp, black and yellow striped insect carrying green thing under its body) are very helpful as well.

Some insects that make early season mud plugs include:

Osmia lignaria suns on a leaf

Osmia lignaria suns on a leaf

Osmia lignaria – Blue Orchard Mason Bee
Family: Megachilidae
Bee characteristics: Metallic blue or blue-green, 1/2 inch long, rotund, resembling a fly
Abundance: Locally common across Colorado, especially near early spring blooming deciduous trees
Seasonality: EARLY spring
Nest diameters: Medium (Large if the medium holes fill up)
Plug composition: Mud that is Chunky in texture and usually medium grey in color
Plug depth: usually Flush with nest entrance, sometimes protruding a smidge
Pollen: Many spring blooming species including willows and apples
Generations per year: 1 (no emergence later in the summer)
References: Many books have been written on this one species including:
Pollination with Mason Bees: A Gardener’s Guide to Managing Mason Bees for Fruit Production by Margriet Dogterom and Mason Bees for the Backyard Gardener by Sherian A. Wright
Notes: Two introduced species, Osmia cornifrons and Osmia taurus also plug with mud. These species have NOT been confirmed for Colorado, although a blurry picture exists of a potential individual from Boulder County seen during spring of 2014. If your early season mud plugger is an O. lignaria sized bee with a brassy metallic orange (copper) color, faint striping on the abdomen, and potentially “tusks” on its face, please get a photo if possible and alert Virginia to this observation immediately (Virginia.Scott@Colorado.Edu).

Osmia lignaria haven

Osmia lignaria haven

Chunky Mud plug by Osmia lignaria

Chunky Mud plug by Osmia lignaria

 

 

 

 

 

 

 

 

Stenodynerus sp. working on nest with plug in tunnel below

Stenodynerus sp. working on nest with another plug in tunnel below

 

Stenodynerus sp.
Family (Subfamily): Vespidae (Eumeninae)
Wasp characteristics: Narrow-tapering, black with yellow stripes, similar to a small paperwasp
Abundance: Somewhat uncommon
Seasonality: Late spring
Nest diameters: Small
Plug composition: Mud that is Smooth (sometimes ridged around the edges) and Concave in the center
Plug depth: slightly recessed (~1/8 inch) from nest entrance
Prey: Caterpillars
Generations per year: multiple with spring nests emerging later in the summer, no renesting?
Notes: At least a dozen species of Stenodynerus occur in Colorado although some of these may nest in the ground

Mud plug made by Stenodynerus sp.

Mud plug made by Stenodynerus sp.

Stenodynerus sp.

Stenodynerus sp.

 

 

 

 

 

 

A male specimen of Chelostoma philadelphi

A male specimen of Chelostoma philadelphi

Chelostoma philadelphi
Family: Megachilidae
Bee characteristics: Small, Elongate 5/16” long, Black
Abundance: We have yet to document this bee in our bee blocks, but the bee occurs in Boulder and nests in wood
Seasonality: During Mock-orange bloom (Philadelphus sp.)
Nest diameters: Small
Plug composition: Mud
Plug depth: Flush
Pollen: Visits only Mock-orange for pollen
Generations per year: 1 (no emergence later in the summer)
References: Krombein’s 1967 Trap-nesting Wasps and Bees
Notes: Boulder is the farthest west this species is known to occur, first documented on the CU Campus in 2002 and again in north Boulder in 2014.

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