Red Cage Fungus

The Red Cage Fungus (Clathrus ruber) is the most familiar of the latticed stinkhorns, a group in the Phallaceae whose fruit bodies expand from an egg-like structure into open, geometric frameworks rather than the more usual stalk-and-cap arrangement. In C. ruber the receptacle is a closed, roughly spherical or ovoid cage of fused, spongy arms, coloured anything from coral pink through orange to deep scarlet.

The fungus begins life as a whitish to pinkish, egg-shaped structure 3-6 cm across, partly buried, attached to the substrate by white cords. Inside, the cage lies folded in a gelatinous layer. Expansion is rapid, often taking only a few hours, and a bed of mulch can go overnight from scattered eggs to a group of open red lattices.

The inner faces of the arms carry the gleba, a dark olive to blackish-green slime holding the spores, and the fruit body gives off a powerful carrion-like odour that carries a long way. The whole structure collapses into a slumped red rag within a day or two.

Fruiting body

The expanded receptacle is a hollow, roughly spherical to barrel-shaped or slightly flattened lattice, 5-20 cm tall, made of 4-8 sided meshes. Arms are spongy, wrinkled or pitted on the outside, roughly triangular in cross-section, and range from pale pinkish-orange to vivid vermilion. There is no cap, no gills and no true stipe.

Gleba

The inner surfaces of the arms are coated with a thick, olive-brown to blackish-green slime that holds the spores. It drips, attracts flies within minutes of the cage opening, and is progressively removed by insects, leaving the lattice paler and cleaner as it ages.

Volva and base

At the base sits the remains of the egg as a white to pale grey, sac-like volva, often half buried, with thick white rhizomorphs running from it into the mulch. Cutting an unopened egg lengthwise shows the folded red lattice embedded in clear jelly between an outer skin and an inner membrane.

Flesh and spores

The arm tissue is soft, chambered and brittle, whitish inside the red outer layer, without colour change on bruising. There is no spore print in the usual sense: spores are carried off in the slime by insects rather than dropped from gills or pores.

Red Cage is a fungus of rich, disturbed, organic ground. It is very common in bark mulch, woodchip beds, compost, leaf litter, hedge bottoms and cultivated garden soil, and also occurs in open woodland and coastal dune scrub. It favours warm conditions and appears from late spring through autumn, often flushing after rain following a warm spell.

Native to southern and western Europe and the Mediterranean, it has spread widely with the horticultural trade and now turns up across North America, particularly California and the southeastern states, as well as Australia, New Zealand, southern Africa and parts of Asia. New sightings are frequently in newly mulched landscaping.

The species is entirely saprophytic, breaking down woody and leafy organic matter. Its mycelium forms conspicuous white cords through mulch and can persist for years in a single bed, throwing up eggs whenever moisture and warmth coincide.

Spore dispersal is by insects rather than air. The carrion-like odour of the gleba mimics decay and pulls in blowflies, flesh flies and beetles, which feed on the slime and depart with spores stuck to their legs and mouthparts or passing intact through their guts. The rapid, pressurised expansion of the cage from the egg is driven by water uptake and the unfolding of pre-formed tissue.

Other latticed stinkhorns are separated by the geometry of the receptacle. Clathrus archeri, the octopus stinkhorn, opens into 4-8 free arms that splay outward from a short stalk instead of forming a closed cage. Clathrus columnatus has 2-5 spongy columns joined only at the top, leaving open sides rather than a mesh. Ileodictyon cibarium and I. gracile form similar closed lattices but are white to cream rather than red, and their cages often detach and roll free of the volva.

Aseroe rubra is red but forms a star of split arms radiating from a disc atop a short stalk. Ordinary phalloid stinkhorns such as Phallus impudicus have a simple white stalk topped by a separate honeycombed, slime-covered cap, quite different from a hollow lattice.