Imperial’s campus in Berkshire, Silwood Park, is a fabulous place to go fungus spotting. The fly agaric (Amanita muscaria) is very common there as there are a lot of birch trees around, and this fungus forms a symbiosis with the roots of those trees:

Fly agarics are rather poisonous (for some value of ‘rather’), by virtue of containing muscimol, and ibotenic acid; the former is a psychoactive dissociative that can cause visual and auditory hallucinations. There is an enormous amount of folklore (i.e. lies) associated with this mushroom that I shan’t bother repeating. There’s not even much evidence that it’s any use for killing flies.