Lethal webcaps

The Lethal webcaps, two species in the genus Cortinarius, belong to the world's most poisonous mushrooms. The species are the Deadly webcap (Cortinarius rubellus, formerly also known as C. speciosissimus) and the Fool's webcap, C. orellanus.

The mushrooms' characteristics are quite common, making these mushrooms difficult to identify, which often leads to fatal poisonings. Young examples of the species often have a veil between the cap of the mushroom and the stem. This veil looks like a cobweb, hence the name. The veil however partially or completely disappears in older specimens. Some other characteristics for each of the mushrooms are given below.

Deadly webcap (Cortinarius rubellus)
Spore color: Rusty brown to orange Cap: 3–7 cm rusty brown to orange. Often has a steeper and darker colored elevation at the top of the cap, but this varies greatly from specimen to specimen Gills: Wide gaps between the gills which can be, but are not necessarily, connected to the stem Location: Rare, but common in temperate parts of northern Europe. Has been encountered as far north as Finnish Lapland. Habitat: Pine woods with acidic soil Other details: Young specimens contain a pale web between the cap and the stem. Sometimes parts of this web can be seen as a yellow ring on the stem or at the edge of the cap. The fruiting body of the mushroom blossoms from mid-summer to late fall.

Fool's webcap (Cortinarius orellanus)
Spore color: Rusty brown to orange Cap: 3–8.5 cm, concave Gills: Similar to those of the deadly webcap Location: Common throughout Europe, rare in the northern parts of Europe. Has been observed as far north as southern Norway Habitat: In forests, around trees where the soil is alkaline or acidic Other details: Young specimens of the Fool's webcap also contain a web between the cap and the stem that partially or completely disappears as the specimen ages.

Toxicity
Both of these mushrooms can be confused with each other and many incidents of mushroom poisoning have occurred where inexperienced mushroom hunters have confused these mushrooms with edible mushrooms such as the chanterelle. One should be especially cautious when picking mushrooms like the cleaned funnel chanterelles as these mushrooms share the same habitat as the deadly webcap and the fool's webcap. In many incidents where this mushroom has been ingested, death has occurred.

In Poland during the 1950s there was a small epidemic where over 100 people became ill. What caused the illness remained a mystery until 1952 when Polish physician Dr. S. Grzymała discovered that everyone suffering from the illness, which had now claimed several lives, had eaten the mushroom Cortinarius orellanus.

Unlike some other species of mushroom, webcaps should never be identified by tasting a small portion of the mushroom. These mushrooms are sometimes stated to be so poisonous that one could be poisoned even after tasting and spitting out a small piece. However, the lethal dose in mice is about 2 g per kg body weight, which translates to about 100–150 g for an adult human.[Holmdahl, 2001] Nevertheless, some mycologists strongly recommend against tasting unknown mushrooms.

The Deadly webcap and the Fool's webcap both contain the toxin orellanin. A characteristic of orellanin poisoning is the long latency; the first symptoms usually don't appear until 2-3 days after ingestion and can in some cases take as long as 3 weeks. The first symptoms of orellanin poisoning are similar to the common flu (nausea, vomiting, stomach pains, headaches, etc.). These symptoms are followed by early stages of renal failure (immense thirst, frequent urination, pain on and around the kidneys), and eventually decreased or nonexistent urine output and other symptoms of renal failure occur. If left untreated death will follow. There is no known antidote against orellanin poisoning, but early hospitalization and treatment can sometimes prevent serious injuries and usually prevent death. If you suspect orellanin poisoning, acting on it quickly can save your life.

Several more mushrooms in the Cortinarius genus are suspected to contain orellanin or other deadly toxins. Among them are Cortinarius callisteus and Cortinarius limonius.