The moniker is well deserved, for they are all just as deadly as they are beautiful, often being a pristine white (at least when young and fresh) and therefore look rather appealing. However, these mushrooms, along with Amanita phalloides, the Death Cap, are responsible for the overwhelming majority of deaths due to mushroom poisoning. For that reason alone, if one is to consider picking wild mushrooms for food, it is imperative that one learn to recognize this family above all others. The toxin responsible for this is alpha-amantin.
Fortunately, they are rather distinctive looking. They are characterized by having a partial veil (annulus), which is a fleshy ring circling the stalk. Perhaps the most tell-tale of the features is the presence of a volva, or universal veil, so called because it is a membrane that encapsulates the entire mushroom, rather like an egg, when it is very young. This structure then breaks into various pieces when the young mushroom expands, thereby leaving parts that can be found at the base of the stalk as a boot or cuplike structure, and warts or patches of removable material on the cap surface. This combination of features, all found together in the same mushroom, is the hallmark of the family. While other families may have any one or two of these features, none have them all.
Unfortunately, most young amanitas look like mature button mushrooms or puffballs. This further emphasizes the importance of slicing all mushrooms picked when mushroom hunting in half.