It probably wasn't this, but was Darwinia what you were thinking of?
i believe you're right. Darwinia had a polygonal graphics and the snakes were the red virus worms. i played it back in the mid 2010s . you're some random user/hacker who finds a way onto a server hosting the darwinnian world on the verge of destruction. The developer ( a clive sinclair like character) grudgingly (more out of desperation) asks for your help in saving darwininia.
The first few tutorial missions tasks players to build a sanctuary and save what's left of the populace before working to save the rest of the world. over time you begin capturing key areas of the world to allow the rebirth of darwinians and ridding the world of the deadly virus. All the while the developer is programming up new units or upgrading existing ones to help in the increasingly threat. Thinking on his feet using unused game assets from somewhere to help.
it played more like cannon fodder as you deploy your squad of anti virus units to kill the monsters and then sent in your space invader like harvester to capture the souls of the slain to be reforged into Darwinians. near the end game there are some strategy elements as you can command the darwinians in basic orders to capture strategic areas, man turrets etc.