White-egg Bird's Nest Identification Guide

The setting and the first impression

You will almost never spot the White-egg Bird's Nest from standing height. It turns up when you crouch to look at something else on a wood-chip path, a mulched border, an old plank, a pile of twigs or a rotting fence rail, and notice that a patch of the surface is stippled with hundreds of tiny ochre-tan cups a few millimetres across, each apparently holding a scatter of pale discs.

The colony structure is part of the first impression. Bird's nest fungi rarely occur singly; they carpet a favourable piece of wood in dense gregarious sheets, and you will usually see a full range of ages together, from closed fuzzy buttons to weathered open cups whose contents have already been dispersed. A hand lens is not optional here. At 10x the whole structure resolves and the identification becomes straightforward; with the naked eye it is little more than a texture.

Reading the young, closed stage

The earliest stage looks nothing like a nest. It is a small rounded cushion, 3 to 6 mm across, densely velvety to shaggy, and coloured a warm cinnamon-buff, tawny or ochre. Sitting across the top is a lid, called the epiphragm, a pale ochraceous membrane stretched like a drumskin over the mouth of the developing cup.

If you find only this stage you can still work with it. Slice one button vertically with a scalpel or a knife tip and you will see the pale discs already packed inside the closed chamber. As the fruitbody matures the lid ruptures and falls away, the mouth opens, and the outer felting gradually wears smoother and paler.

Reading the mature cup

A mature cup is 5 to 10 mm tall and 5 to 8 mm wide at the mouth. The profile is the first thing to note: it is more or less cylindrical to slightly barrel or crucible shaped, with fairly straight walls and a mouth that is not dramatically flared. The rim is usually even, sometimes minutely fringed with the torn remains of the lid.

The outer wall is pale ochre to tan or cinnamon-buff, felted when young and becoming nearly smooth with weathering. Now tip the cup toward the light and look at the inner wall. In this species it is smooth, pale, whitish to buff or faintly greyish, and completely without longitudinal grooves or pleats. That smooth pale interior, seen under a lens, is the character that carries most of the identification.

Reading the eggs

The eggs, properly called peridioles, are the packages of spore-bearing tissue. Count and look at them closely: there are typically five to fifteen per cup, each 1 to 2 mm across, disc-shaped to lens-shaped and slightly flattened rather than spherical.

Their colour is the second key character. They are whitish to pale cream or very pale buff, because each is wrapped in a thin white outer coat. Against the pale inner wall of the cup they can be surprisingly hard to see, which is a useful observation in itself; in the striate and dung-loving bird's nests the eggs are dark grey to blackish and stand out sharply.

The funicular cord test

This is the one manipulation worth doing in the field, and it is decisive. Under a lens, take a fine needle, a pin or the tip of a knife and gently prise one peridiole away from the cup wall.

In the White-egg Bird's Nest each egg is tethered to the wall by a funiculus: a coiled elastic cord, usually invisible until it is stretched, that pays out as a fine thread as you lift the egg away. It resists, extends, and often ends in a sticky pad. This cord is the mechanism behind splash dispersal, in which a raindrop striking the open cup ejects an egg, the cord unspools in flight, and the sticky end wraps around a nearby stem or twig.

If the eggs lift out freely with no thread at all, and instead sit in a clear jelly-like matrix, you are looking at a different genus.

Flesh and colour change

There is no fleshy tissue to speak of. The cup wall is tough, leathery and thin, and it does not bruise, bleed, exude latex or change colour when cut. A vertical section is still worth taking, though, because it shows the wall to be built of a single distinct layer rather than the obviously three-layered wall of some relatives, and it lets you confirm the presence of eggs in unopened buttons.

Why you cannot take a spore print, and what to do instead

A conventional spore print is impossible with a bird's nest fungus. The spores are not exposed on an open surface; they are sealed inside the peridioles and are only released when an egg lands elsewhere, sticks, and eventually breaks down. Standing the cup on paper overnight will give you nothing.

Instead, do the equivalent under a microscope if you have one. Crush a single peridiole on a slide in a drop of water, tease it apart with a needle and look at the internal spore mass: the spores are colourless, thick-walled, smooth and broadly ellipsoid. In the field, substitute the visible characters that do the same job: egg colour, egg count, the smooth inner wall and the funicular cord.

Substrate and season

The White-egg Bird's Nest is a decomposer of dead plant material, with a strong preference for wood in contact with the ground. Wood-chip mulch and bark paths are the classic modern habitat; it is also common on fallen twigs and branches, old boards, fence rails, sawdust piles, and occasionally on dead herbaceous stems, straw and stubble.

It fruits from early summer through to late autumn, and because the cups are tough and weather-resistant, old empty examples persist through winter and can be found long after fruiting has stopped. Dense colonisation of a single mulched bed is normal, and the same bed will often produce for several successive seasons until the chips are exhausted.

Separating it from its closest look-alikes

Fluted bird's nest (Cyathus striatus). The most frequent confusion. Its cups are larger and distinctly trumpet-shaped with a flaring mouth, the outer wall is coarsely shaggy with brown hairs, and above all the inner wall is conspicuously grooved with vertical pleats. Its eggs are dark grey to blackish. The White-egg Bird's Nest is smaller, straighter-sided, smooth inside and pale-egged.

Field bird's nest (Cyathus olla). Larger again, grey to grey-brown, with a widely flared and often outward-curled mouth. The interior is smooth but grey rather than whitish, and the eggs are large and dark grey.

Dung bird's nest (Cyathus stercoreus). Dark, smooth-walled inside, with blackish eggs, and found on dung or heavily manured ground rather than wood chips.

Nidula species. These look closest in colour but fail the cord test: their many small eggs sit loose in a gelatinous matrix with no funiculus at all, and the cups are usually broader and more barrel-like.

Cannonball fungus (Sphaerobolus stellatus). Much smaller, orange, and opening as a tiny star holding one single ball, which is shot away rather than splashed out.

Non-fungal confusions. Young closed buttons can be mistaken for insect galls, seed capsules or slime mould fruitings. Slicing one open and finding a chamber full of pale discs resolves it instantly.

Field checklist

1. Wood chips, twigs, boards or straw; dense gregarious colonies; summer to late autumn.
2. Young stage a fuzzy ochre cushion sealed by a pale lid.
3. Mature cup 5 to 10 mm, cylindrical to crucible-shaped, not strongly flared.
4. Inner wall smooth and pale, never grooved.
5. Eggs 5 to 15, whitish to pale buff, disc-like.
6. Each egg tethered by a stretchy funicular cord when teased with a needle.