I started looking up some crazy things I remember reading about spiders jumping to their deaths (more on that later), but when I went back and watched the footage, they certainly were not making rapid descents, as the descriptor 'raining' would suggest. The biologist quoted also described them as making 'sheet webs' which seems to explain this. Either way, it's really something to see.
Article Link: Think Nemo's bad? In Brazil it's raining spiders
So, the memory this triggered for me was of a brain eating fungus that infects a particular spider host. When the brain is infected the spider eventually climbs to the tallest tree it can find and jumps to its death. Unfortunately I couldn't find anything on that phenomenon and got side tracked on the two following (random science) topics.
Mexican Jumping Death Spider
If this species (not actually originating in Mexico) chooses to jump and successfully reaches the apex of the jump, it will die at that point in its jump. If it jumps or falls but does not consciously choose to do so, it will not die. If it chooses to jump but does not reach the apex or is in some way obstructed from successfully jumping, it also will not die.
"The Mexican jumping death spider is a rare sight to see in Waterloo, and chances are if you see one, it will die trying to hide from you. Please, for the sake of the species, do not look for them; they are an endangered species"
Brain eating ameoba
This ameoba is fatal for the rare swimmer that contracts it in US freshwater, with the threat each year subsiding with the onset of winter. But a couple of people have contracted it through their neti pots. Only a couple, but still....I think I'll be using distilled water from now on.