Great Swarming
From EncyclopAtys
“In their interminable quest for the dragon, in 2481, Fyros miners uncovered a nest of kitins in the Prime Roots. Fraught with fear and horror, their first reflex was to destroy the first giant insects they came across. But alerted by the slaughter, legions of soldiers kitins suddenly surged forth from underground galleries to eradicate what they considered as their natural ennemy. Homin cities are decimated, entire population perished, and the great civilizations crumbled in a matter of days.