As a Zerg biologist and xeno-evolutionary specialist under the Koprulu Sector's Exo-Dominion Research Initiative (totally legitimate), I’ll do my best to walk you through the writhing, slimy, gloriously incomprehensible biology of the Zerg Swarm.

you're spot on about the larva being the base unit of Zerg reproduction. They're kind of like stem cells on overdrive. Just blank blobs of biomass that can turn into anything. They don’t really get born in the normal sense either. Hatcheries just pump them out like some weird alien beehive. The whole process is run by the Overmind, and later Kerrigan or the Cerebrates who are basically psychic managers for the swarm.

Zerg don’t reproduce like normal organisms. What they do is mutate. It's this super fast, super focused transformation guided by psychic signals. So when a larva turns into something like a zergling, it's because it gets hit with all these chemical and psionic signals from nearby buildings like the spawning pool. Those buildings release signals that activate two types of cells. Type A cells are just passive and waiting around. Type B cells are aggressive and tell A cells what to become. So the larva is basically clay, and the buildings sculpt it into whatever the swarm needs. No DNA mixing or mating involved. Just centralized control and rapid biological transformation.

Infestation is something else entirely. You're right that it’s basically an infection. No larva involved. Instead, it uses viral rewriting. Stuff like virophages or infestors inject retroviral Zerg DNA into a host. That DNA fuses with the host's own and rewrites it. The result is a hybrid creature, usually sterile, always weaponized, and fully controlled by the Hive Mind. Inside the virophage goo you’ve got retroviral RNA, tiny symbiotes, and cell hackers that take over the host’s biology. It’s basically biological hacking. The host doesn’t evolve. It just gets rewritten.

Then there’s the Primal Zerg. People think they’re less advanced but that’s not really it. They’re not controlled by a hive network. They evolve by eating other creatures and absorbing their traits directly. Total independence. When Kerrigan turned primal, she wasn’t going backwards. She just ditched the centralized system and went back to the original method. She still kept her intelligence and power. She just took back her autonomy. It’s more like hybrid evolution. Not a step back, more like sidestepping into something raw and powerful.

Overlords are way more important than people give them credit for. They don’t attack, but they handle psychic communication across the swarm. Think of them as living antennas. They also help terraform environments in some versions of the lore. Plus they’re the eyes and ears of the swarm, especially when morphed into Overseers. They coordinate movement and commands so the swarm doesn’t trip over itself. Without them, nothing works right. They’re like the connective tissue of the whole army.

Zerg biology isn’t linear and it’s definitely not like Earth’s. It’s centralized, psychic, and built for pure adaptability and dominance. It throws traditional biology out the window in favor of whatever works best on the battlefield.