fascinating - thank you for sharing....
we have experienced mass suicide by worms 'herding'
sometimes in the summer months we get a few thousand worms all in a big heap, because there are so many, the middle ones die (probably suffocation)
they quicky start to compost - and create heat - which spreads outwards and causes more and more to die.
Within a few hours you can have a lot of dead worms, the only solution seems to be - getting your hands in and pulling them apart.
Im not sure if its the heat that make them huddle together - a survival instinct - that always goes wrong ?
Ronnie