wasp nest slime mold

Wasp nest slime mold is a common and widespread plasmodial slime mold. It is found in Europe, Asia, Africa, Australia, and North and South America. In the United States it is common east of the Great Plains, including Minnesota, less common in the west. It grows in open forests on dead and rotting wood, especially hardwood.

The fruiting body (sporocarp) may be attached directly to the substrate (sessile) or rise in a densely crowded group of up to twelve on a common stalk (stipitate).

The spore-producing structures (sporothecae) are less than ⅛″ (2.5 mm) in height, and about 1 ⁄32″ (0.4 to 0.7 mm) in diameter. They are almost cylinder-shaped or cone-shaped to almost egg-shaped, and have a distinct convex lid (operculum) on top. The outer skin consists of two or three layers: an outer, tough, cartilaginous, dark red or reddish-purple to nearly black layer; and an inner membranous layer. The operculum is shiny, iridescent, and dark red or reddish-purple to nearly black. When mature, it swings open like a jack-in-the-box, and the interior expands outward. The expanded interior consists of a few fibers (capillitia) interspersed with the spores. The capillitia are very long, coiled, and red. The spore mass is bright red or rust-red. When it dries out, the spores are disbursed by wind. Eventually, the expanded portion disintegrates. What is left looks like the nest of a paper wasp, giving this slime mild its common name.

Open forests. Dead wood.

Sources

7, 24, 26, 29, 30, 77.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, 7/1/2025).

Widespread and common

Higher ranking
There is ongoing disagreement about the classification of slime molds above the rank of genus. The ranking above follows Global Biodiversity Information Facility (GBIF), Catalogue of Life (COL), MycoBank, MycoPortal, and iNaturalist. It is not in agreement with Index Fungorum or ITIS, neither of which agree with GBIF or with each other. iNaturalist lists the Superorder and the Subclass. GBIF, COL, MycoBank, and MycoPortal do not.

Species gender
Index Fungorum, GBIF, COL, and MycoBank use the species epithet vesparia, which is the feminine spelling. ITIS and MycoPortal use the species epithet vesparium, which is the neuter spelling. iNaturalist recently made the taxon change from Metatrichia vesparia to Metatrichia vesparium.

Wasp Nest Slime Mold, Metatrichia vesparium
microcosmic

Location: Cass County