The Fly Agaric, Amanita muscaria. The fly agaric is poisonous. It is known to cause hallucinations, violent stomach upsets, uncontrollable muscle spasms and could be fatal. It has been used as a fly killer - hence the name. Small pieces of the fungi were added to a saucer of milk. Flies came to feed from the saucer and were killed. Did you know? The name 'Toadstool' might make you think that toadstools got their name from being a piece of amphibian furniture, but in fact 'toad-stuhl' is a German name, which means seat of death!