At any stage of playthrough biters can become a huge obstacle on your way. And because of raw potential they can easily get out of control.
So how to make it easier to balance? There is possible solution: additional stat called "Stamina".
[ Biters / Spitters ]
These are actually pretty fine (even the behemoths).
Stamina can be added to make them run fast only for limited amount of time.
Bonus usage: give small and medium biters an ability to climb on (technically - load in) big and behemoths biters. So huge bugs can deliver smaller (and less endurant) pals at your base fresh and ready to attack.
Bonus usage: biters can use stamina to swim, but "transport" biters is also almost unsinkable. Awesome addition for future water expansion.
[ Spawners ]
Probably the main problem of topic. Endless avalanche of cannon fodder. And you cannot just nerf the rate, this will not solve problem.
Stamina can be added as a resource to spawn biters.
Bonus usage: Spawner consumed all it's stamina become inactive until full recovery.
Bonus usage: Pollution will increace stamina regeneration rate.
Bonus usage: Another active spawners nearby will decrease stamina regeneration rate.
[ Worms ]
Ugh. This is the real reason of this topic. The concept of worms is just unhealthy: in order to attack you must got a hit (or goddamn bunch of them) OR you will not get damage at all, making worms itself completely useless.
Stamina can be added as an ammo.
Bonus usage: Finally, Distraction Capsules. Drop some of them to allow these organic turrets to unload and then enjoy lowered rate of fire.