So, to counter that, I'd like to propose some ideas I'd been stewing on for a while.
- Hive Retaliation - Pretty much what it says on the tin; isn't it weird how often, Hives that would be just outside aggro-range, seemed utterly impassive to how you started killing their brethren. So instead, how about after a certain 'evolution tick' (maybe 0.2/0.3), as you begin to kill Spawners in their base, it starts winding up a 'death cry', which scales based on cumulative number of spawners, biters, spitters and worms, and is released upon a measured length of inactivity (say, ~5 seconds). When this happens, it triggers every Hive in a cumulative radius proportionate to the number of enemies killed, to begin an 'Attack Wave'.
- Evolution does more than 'Little Biter, Big Biter' - One of the controversial features of another game; Killing Floor 2, has it's enemies scale in difficulty by adding new layers or move sets to their behavior, so say for in Factorio's case, Small Biters could get a moderate speed boost equal to one Exoskeleton at .6 Evolution, or Spitters could get a slight 'Damage over Time' at .4. The idea here is to make the indigenous wildlife actually seem like they're evolving, learning, finding new defense mechanisms, not just becoming 'more adept at taking bullets to the face'.
- A more 'natural' and counterable expansion - So for this, I'd like to introduce the first type of new Biter; the Broodmother. What this fellow does, is spawn from a nearby hive, and move into a chunk containing pollution, before sending small waves of biters out in a relatively large radius scouting for pollution (Miners, Pumpjacks, Furnaces, Engines) or damage sources (Turrets). If it remains inactive for x amount of minutes, the Brood Mother becomes a Spawner/Nest and begins to transition into the makings of a Hive... However; If it runs into one such source, it immediately enters 'Siege Mode' where, over the course of every 2-3 minutes it'll send small (5-10) numbers of Small Biter and Spitters at the target until it's dead. Basically the idea is that these fellows will practically sit just outside your Laser Turrets range, besieging them constantly until they get through, and offering a new sort of pressure, and potential drain on resources as more production is diverted to replenishing ammunition.
Now that's the mainstay of the 'general' ideas for Biters out of the way, but in the wake of Nuclear Fuel and Weapons, I've noticed one thing we're lacking from these; Consequence.
First and foremost; I'm a huge fan of GotLag's Reactors mod, but I do feel like the implementation of Nuclear was actually ideal from a production and setup standpoint; unique heat pipe mechanics, and not having to faff around so much with inserters, pumps and circuits to ensure the reactor is getting the right amount of fluids (Just wish there was smokestacks lol, I miss those)
So for the sake of consequences and giving some impression of power to these awesome forces, I'd like to propose the following;
What Irradiation does, is when a medium (Uranium Explosive Tank Shell) to large (Atomic Bomb) munition is detonated, it leaves an 'irradiated zone' in its midst. This Irradiated zone is several times larger than the initial blastwave of the weapon, but it's effects are immediate;
- All trees in the irradiated zone quickly begin to wither and die as if at max pollution, tapering out chunk by chunk.
- An 'irradiated' entity is placed at the center of explosion with a size of about half that of the original explosion, it acts as a damage over time source and will gradually hurt both player and Biter alike, discouraging building over former blast zones for a set time. It will 'linger' for anywhere between 15 minutes (Tank Shell) to 1-2 Hours (Atomic Bomb)
- Irradiates ore caught in it's blast range, lowering potential yields by 3~5% on average on each entity hit by the blast wave.
- Applies a subtle 'emissive' glow to the irradiated area, making it feel unnatural and sick, and causing a slowly intensifying geiger counter sound the closer to the center of the explosion you get.