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Deadly Webcap

Deadly Webcap

Deadly WebcapDeadly
Scientific nameCortinarius orellanus
FamilyCortinariaceae
Portuguese nameCortinário-mortal
English nameFool's webcap, Deadly webcap
SeasonSeptember, October, November
HabitatOak forest, Chestnut forest
Look-alikesChanterelle

Fool’s webcap (Cortinarius orellanus) — deadly poisonous mushroom

DEADLY POISONOUS MUSHROOM! Symptoms may appear 2–14 days after ingestion, when the connection to mushrooms is no longer obvious. Kidney damage is often irreversible, requiring lifelong dialysis or kidney transplantation.

Description

Cortinarius orellanus (deadly webcap, fool’s webcap) is one of the most insidious poisonous mushrooms in Europe. Its main danger lies in the exceptionally long latency period (up to 2–3 weeks), which means patients often fail to connect their symptoms to mushroom consumption. A small, inconspicuous rusty-brown fungus that is easily mistaken for a harmless species.

Cap

  • Diameter: 3–8 cm
  • Shape: convex, later flattened, sometimes with a slight umbo
  • Colour: rusty-brown, warm orange-brown
  • Surface: dry, finely scaly, with radial fibres
  • Margin: thin, sometimes slightly inrolled

Stem

  • Height: 4–9 cm
  • Width: 0.5–1.5 cm
  • Colour: yellowish, lighter than the cap
  • Ring: absent
  • Cortina: cobweb-like veil in young specimens, disappears quickly
  • Surface: with longitudinal fibres

Flesh

  • Colour: yellowish, no colour change when cut
  • Smell: faint, unremarkable (described as “radish-like” or “mealy”)
  • Taste: mild or slightly bitter

Spore print

Rusty-brown.

Toxicity

Toxin

  • Orellanine (3,3’-4,4’-tetrahydroxy-2,2’-bipyridine-1,1’-N-oxide) — first isolated in 1962, structure confirmed in 1979
  • Heat-stable — not destroyed by cooking

Mechanism of action: orellanine rapidly concentrates in the kidneys and causes oxidative stress in renal tubular cells, leading to necrosis. Toxicity is cumulative and irreversible.

Course of poisoning

PhaseTimeSymptoms
1. Latent2–14 days (up to 3 weeks!)Asymptomatic. Toxin accumulates in the kidneys
2. Initial2–14 daysThirst, dry mouth, headache, flank pain
3. RenalDays–weeksOliguria (reduced urine output), elevated creatinine, proteinuria
4. Renal failureWeeks–monthsProgressive renal failure requiring dialysis

Mortality: with modern treatment (dialysis) — low, but the irreversibility of kidney damage makes this mushroom exceptionally dangerous. Many patients require lifelong dialysis or kidney transplantation.

Historical note

A mass poisoning of 135 people in Poland in 1957 first drew serious attention to the toxicity of the genus Cortinarius. 11 people died.

Where and when

Season

  • Main season: September–November
  • Fruits after autumn rains

Habitats in Portugal

  • Primarily in the north of the country — under oaks and chestnuts
  • Forms ectomycorrhiza with broadleaf trees, especially oaks (Quercus spp.)
  • Prefers acidic soils in warm broadleaf forests
Presence in Portugal requires confirmation. The species has been confirmed on the Iberian Peninsula (Spain) and is described as “more frequent in southern Europe”. Ecologically suitable habitats exist in Portugal, but direct scientific records for Portuguese territory are insufficient.

Look-alikes

SpeciesDifference from deadly webcap
Chanterelle (Cantharellus cibarius)Chanterelles have false gills (blunt, forked, decurrent), not true gills. Egg-yellow colour, grows on soil
Other Cortinarius spp.Many species in the genus Cortinarius look similar. Expert recommendation: avoid collecting any webcaps for consumption

Safety rule

The genus Cortinarius contains over 2,000 species, many of which are difficult to distinguish. The only reliable way to avoid poisoning is to not collect webcaps at all.

Image sources
  • cortinarius-orellanus.webp — Fool’s webcap (Cortinarius orellanus) — deadly poisonous mushroom. Author: Michaelll. License: CC BY-SA 2.5. Source

See Also

Habitats:

Related articles:

Sources

  1. Prast H. et al. — Toxic properties of the mushroom Cortinarius orellanus // Archives of Toxicology, 1979
  2. Dinis-Oliveira R.J. et al. — Orellanine: from fungal origin to cancer treatment // Toxicology, 2023
  3. Holmdahl J. et al. — Long-term clinical outcome for orellanine poisoning // BMC Nephrology, 2017
  4. CIAV — Centro de Informação Antivenenos, INEM Portugal
  5. BioDiversity4All / GBIF — species records
  6. First-Nature — Cortinarius orellanus identification

Disclaimer: Identifying mushrooms from descriptions and photographs on the internet is not a substitute for consulting an experienced mycologist. The authors assume no responsibility for the consequences of collecting and consuming mushrooms. If you suspect mushroom poisoning, call 112 immediately.

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