Professor Poledread was a wizard at the Unseen University many years before the current time.
According to Prof. Poledread, Hivers were formed in the first seconds of Creation. They are not alive, but have the shape of life. Most often they end up at the bottom of deep seas, or in the belly of volcanoes, or drifting through the hearts of stars. They have no body, no brain, no thoughts, but they do have the ability "to crave and to fear." They also have memory.
Dr Bustle believed this to be wrong, and set about disproving he collegue's theories by trapping a Hiver of his own to study and research. Apparently he succeeded, but the Hiver took over his body, and led to Dr Bustle's very sticky end.