The Great Swarm

There's barely any Factorio mods, so I decided to make the biters. They have a lifecycle and some horde events during nighttime. The behemoths can go through your walls while the smaller ones just climb like normal insects.

Pollution gathers based on how many blocks are broken and placed by the player. Along with that, the biters can also gather points through feeding upon the local wildlife. More pollution points will cause stronger biters to spawn, eventually resulting in great behemoths being summoned.