Why would a mushroom be named “fly agaric”? I couldn’t find a clear answer to this, but “fly” could refer to its historical use as a fly killer, since it contains ibotenic acid. Or it could refer to the delirium it induces if eaten. “Agaric” roughly translates to “mushroom”—it refers to a fungal fruiting body that has a cap that is clearly differentiated from the stalk, with gills on the underside of the cap. In any case, amanitas are attractive, common, and dangerous. Amanitas are the iconic toadstool, or poisonous mushroom.
Identification: Caps are bright red in western varieties, orange or yellow in northern and eastern locales; with white, warty spots. They reach 1¾-12" (5-30 cm) in diameter, and can reach 12" (30 cm) in height. There are many varieties of amanitas—for a detailed key, see Michael Kuo’s at mushroomexpert.com.
Edibility: Poisonous This species is not as poisonous as several of its relatives, and fatalities from eating them are rare, but they nevertheless cause a wide range of unpredictable symptoms. From Wikipedia:
... Depending on habitat and the amount ingested per body weight, effects can range from nausea and twitching to drowsiness, cholinergic crisis-like effects (low blood pressure, sweating and salivation), auditory and visual distortions, mood changes, euphoria, relaxation, ataxia, and loss of equilibrium.
That’s if the effects are mild. Seizures, coma, and possibly death can occur with stronger doses. The effects of a given dose vary enormously from person to person. There is no antidote. Despite the risks, many earlier peoples have consumed it for its psychoactive effects, a practice that continues to a limited extent even today.
Amanita muscaria lacks significant amounts of amatoxins and phallotoxins, which make some of the other amanitas so deadly. But they contain a chemical cocktail I wouldn’t mess with:
Amanita muscaria on Mykoweb.com: the Fungi of California
Amanita muscaria on Tom Volk's Fungi site, at the Department of Biology at the University of Wisconsin
Amanita muscaria on Michael Kuo's MushroomExpert.com
Amanita muscaria on Wikipedia
Amanita muscaria on RogersMushrooms.com
Turner, Nancy J.; von Aderkas, Patrick, The North American Guide to Common Poisonous Plants and Mushrooms: How to Identify More than 300 Toxic Plants and Mushrooms Found in Homes, Gardens, and Open Spaces, Timber Press, 2009, p. 79
1From The North American Guide to Common Poisonous Plants and Mushrooms; see reference above
Amanita muscaria description by Thomas H. Kent, last updated 17 Jun 2016.