Dung-loving Bird's Nest
Cyathus stercoreus
Also called dung bird's nest, black-egg bird's nest, dung-loving cyathus
A small dark bird's nest fungus, shaggy when young but smooth-walled inside, distinguished by its jet-black eggs and its habit of growing on dung and heavily manured ground.
Overview
Cyathus stercoreus is the dung specialist among the bird's nest fungi, its epithet meaning "of dung". Fruiting bodies are small tapering cups that appear on animal droppings, well-manured soil, old compost, and sandy or disturbed ground enriched by grazing animals. They often occur in tight troops, sometimes covering a single dropping or patch of enriched sand.
The species belongs to the Nidulariaceae in the Agaricales and shares the family's rain-powered dispersal system, with spores sealed inside hard peridioles that are flung from the cup by falling drops. In this species the peridioles are unusually dark — matt black — and comparatively numerous.
Its diagnostic mix is a shaggy young exterior combined with a smooth, ungrooved inner wall, black eggs and a dung-associated habitat. Under the microscope it is also notable for having exceptionally large spores compared with its relatives, which fits its life cycle of passing through the guts of grazing animals.
How to identify it
Fruiting body
A narrow, tapering cup or inverted cone 6–15 mm tall and 4–8 mm wide at the mouth, often slightly constricted below the rim and narrowing to a small basal pad of mycelium. Cups usually grow gregariously, sometimes in dense crowds.
Outer surface
Young cups are conspicuously shaggy with tawny to dark brown or greyish hairs, giving a rough, woolly look. These hairs wear away readily, so older specimens can appear almost smooth and dull greyish brown — a change worth remembering when comparing with other species.
Inner surface
Smooth and unfurrowed, dark grey to blackish or lead-coloured, often with a slight shine. The absence of the vertical grooves of Cyathus striatus is a key character.
Lid and peridioles
An ochre to whitish membrane closes the immature cup and tears away at maturity. Inside are typically numerous peridioles, each 1–2 mm across, flattened and distinctly matt black, without the pale outer skin seen in some relatives. Each is tethered by a coiled funiculus. Spores form inside the peridioles and are notably large for the genus, so no conventional spore print is taken.
Where and when it grows
As the name implies, this species is strongly associated with dung and dung-enriched substrates: cow, horse and rabbit droppings, manure heaps, old compost, heavily manured garden and field soil, and the sandy ground of dunes, paddocks and grazed waste places. It also turns up on sand and gravel where organic enrichment is present, and occasionally on straw or wood chips mixed with manure.
Cyathus stercoreus is cosmopolitan, recorded from Europe, the Americas, Asia, Africa and Australasia, and is generally more thermophilic than the woodland bird's nests. Fruiting bodies appear from summer into autumn wherever moist, enriched substrate is available, and in warm climates they can appear over a longer season.
Ecological role
This is a coprophilous saprotroph, decomposing the plant fibre in herbivore dung and other richly organic matter. Its mycelium develops within the dropping or manured soil, and once the substrate is well colonised the cups appear on the surface.
The life cycle exploits grazing animals directly. Rain splashes the black peridioles out of the cup; the trailing funiculus, with a sticky pad at its tip, wraps around a grass blade or stem and fixes the package at grazing height. When the plant is cropped by a herbivore, the peridiole passes through the gut, its tough wall is broken down, and the large, thick-walled spores are deposited in fresh dung — precisely the substrate needed to start again.
Similar species
Cyathus striatus is separated at once by the strong lengthwise fluting inside its cup and its persistent coarse shaggy brown exterior; it also grows on woody debris and mulch rather than dung. Cyathus olla has a much wider, flaring, goblet-shaped grey cup with a smooth interior but only a few large lead-grey peridioles, and it favours plant litter and soil.
Crucibulum laeve is squatter and crucible-shaped, tawny-ochre and felty outside, pale inside, with white peridioles. Where habitat overlaps on manured ground, the black peridioles and smooth dark inner wall of C. stercoreus remain decisive. Weathered cups whose hairs have rubbed off can look deceptively smooth outside, so check the interior and the peridiole colour rather than relying on the exterior alone.