Brewer's: Red Snow
and Gory Dew. The latter is a slimy damp-like blood which appears on walls. Both are due to the presence of the algae called by botanists Palmella cruenta and Haematococcus sanguineus, which are of the lowest forms of vegetable life.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894