Geography and distribution
Widespread in north-temperate regions, throughout Europe, Iceland, northern Asia - including Siberia and Korea - North Africa, and western North America. Inadvertently introduced with forestry into South Africa, Australia and New Zealand. In some places where introduced it is considered a pest species in native forests where it forms mycorrhizas with native trees, including species of Nothofagus, and adversely affects native fungi.
Cap: The cap is at first hemispherical, covered by a universal veil which is whitish and somewhat warty, and expands gradually to measure 7-15 cm across. The mature cap is convex to flat, red or scarlet, more rarely orange to orange-red or fading to orange-yellow with age or in wet weather. It is striate (grooved) at the margin, and bears white, fluffy, scale-like patches of the universal veil, which may be lost with age or wash off in wet weather.
Gills: The gills are free, white or whitish and closely spaced.
Stipe: The stipe (stalk) is 10-18 x 1-2 cm, white, cylindrical, usually slightly felty-scaly, with a well-developed, white or yellow-edged ring or annulus, and a bulbous base bearing scale-like remains of the volva.
Spores: The spore deposit is white. The spores are broadly ellipsoid to subglobose, smooth, not amyloid (not darkening in iodine), and 8-12 x 6-9 µm in size.
Two named varieties occur in Britain: Amanita muscaria var. aureola which has an orange-yellow cap, and A. muscaria var. formosa, which is a rather rare brown or yellow-brown form with a slightly tinted veil.
Mycorrhizas and host trees
Like most Amanita species, as well as a wide range of other fungi, A. muscaria is ectomycorrhizal, forming an intimate, mutually beneficial relationship with the roots of its host trees. In its native range in the temperate northern hemisphere, its hosts include birches and various conifers, including species of Abies, Cedrus, Picea and Pinus.
It has long been established outside its native range in parts of the southern hemisphere, especially in south-eastern Australia, including Tasmania, and in New Zealand. Here, it has spread from the cultivated pine plantations (Pinus radiata), with which it was apparently originally introduced, to form associations with various other introduced trees, including broad-leaves, conifers and Euclayptus. In New Zealand it has become established with Nothofagus and possibly other trees native to the area, and may aggressively compete with, and oust, native ectomycorrhizal fungi. It is regarded as a pest species in New Zealand.
An older Amanita muscaria showing the veil mostly lost, and colours fading (Photo: Paul Cannon)
Fly agaric is well known to contain psychoactive alkaloids, and has a long history of use in Asia and parts of northern Europe for religious and recreational purposes. It has also been identified with ‘Soma’, a sacred and hallucinogenic ritual drink used for religious purposes in India and Iran from as early as 2000 B.C., and the subject of a Hindu religious hymn, the Rig Veda. The identity of Soma is controversial but is thought by the American author Robert Wasson to be made from A. muscaria.
Since medieval times, fly agaric has also reportedly been used to attract and kill flies, and the ibotenic acid it contains is indeed a weak insecticide. According to the British mycologist John Ramsbottom, it was also used in England and Sweden for getting rid of insects.
Other anecdotal uses of fly agaric include its use as a treatment for sore throats, and arthritis, and as an analgesic. Fruitbodies also provide an important food source for invertebrates, especially for the larval stages of a range of Diptera (flies), particularly in the families Anthomyiidae, Cecidomyiidae, Heleomyzidae, Mycetophilidae, and some Syrphidae.
Toxicity of fly agaric
Fly agaric is psychoactive and hallucinogenic, containing the alkaloids muscimol, ibotenic acid and muscazone, which react with neurotransmitter receptors in the central nervous system. These cause psychotropic poisoning which may be severe in some cases although deaths are very rare. It also contains small amounts of muscarine, the first toxin to be isolated from a mushroom, and first isolated from this species. This causes sweat-inducing poisoning, stimulating the secretory glands and inducing symptoms which include profuse salivation and sweating. These symptoms can be treated by using atropine but this should not be used in cases of Amanita muscaria poisoning because it increases the activity of muscimol.
It should be cautioned that faded specimens of A. muscaria, with orange caps, have sometimes been misidentified as Amanita caesarea (Caesar’s mushroom) which is a sought-after edible species found in southern Europe and North Africa. It does not occur in Britain, and is easily distinguished from A. muscaria by its yellow gills and large white volva.
Fly agaric at Kew
A young fly agaric, with an unexpanded cap and thick veil (Photo: Paul Cannon)
Amanita muscaria is frequent in the Gardens wherever suitable habitat includes its favoured tree partners. Fruiting occurs during autumn, mainly from September to November. The fruitbodies, with their characteristic red, white-spotted caps and white, ringed stem, are quite distinctive and unlikely to be confused with other species.
Dried collections of A. muscaria from throughout its range are maintained in Kew's Fungarium. These specimens are made available for study by mycologists from around the world, by appointment.
Other British species
Amanita is a large genus, almost worldwide in distribution, and includes the ‘grisettes’, which lack a ring on the stem and were once placed in the genus Amanitopsis. At least thirty species occur in Britain, most of them being ectomycorrhizal (forming a relationship with tree roots) and important forest fungi. They include well-known and common species such as the blusher (A. rubescens) and the tawny grisette (A. fulva) as well as the infamous death cap (A. phalloides), which is amongst the most poisonous of all fungi. Some species are scarce and little-known, and five are on the preliminary Red Data List (2006), including A. friabilis and A. vittadinii which are regarded as ‘Endangered’ and ‘Critically Endangered’ respectively.
Although some Amanita species are regarded as edible, it is wise to avoid the genus from a culinary viewpoint as the various species contain a range of different toxic metabolites. For example, blusher contains haemolytic compounds which may cause break-up of red blood cells, although these compounds are readily denatured by heat so that well-cooked fruitbodies are edible. The toxic alkaloids found in A. muscaria also occur in A. pantherina (panther cap), whereas death cap and its relatives (A. virosa in Britain) contain cyclopeptides, amatoxins and phallotoxins, compounds which are not destroyed by heat and cause severe liver damage leading to death if not treated early.