Vice Admiral,
I've seen your speeches and read your memoirs – you are a man of few words and harsh measures. I can respect that. I also know that you appreciate a similar bluntness of approach in all matters – military, political, personal, doesn't matter. So forgive me if I don't exactly cop to the same kind of sycophantic or pedantic bullshit of my peers; pretty much all information on the zerg that can be considered worthwhile is classified and thus inaccessible.
Since you told me to "come up with a fucking workaround," I have done just that by crawling every inch of the extranet I had available to me from remote access through a colonial adjutant. I have spent 400 man hours watching badly shot handheld footage, salarian horror films that look like they were made on a shoestring budget by fucking Ed Wood, and reading various secondhand reports and public databases on zerg organisms in order to try and construct a coherent narrative that, let me be clear, I was told from DAY ONE would likely be irrelevant.
Normally I would ask you to make good use of the intel I got, but honestly, just fuck off. This was hard work that I don't expect you to even look at, let alone value. Just take it and leave me to my migraines.
Love,
Captain Patrick Harris
The Zerg Swarm
Ah yes, the alien species responsible for bending the galaxy over for just a few months, completely changing the political landscape as a consequence. I've seen other intelligence reports, Vice Admiral, and I know normally we would discuss the history, politics, or overall military doctrine here, but honestly, they're just a horde of space bugs. That might not have been true during the Great War, but in the present, all guiding intelligence behind these things is long gone.
So: historically, the Zerg Swarm seemed to have been governed by entities known as Cerebrates (big ass bug brains) who answered to the larger Overmind. These Cerebrates could point their respective zerg broods in the direction of the enemy and even orchestrate strategy and tactics to some degree: the published memoirs of the turian general, Desolas, make fighting the zerg back then seem like an actual war; a back and forth bout involving allocation of resources, troop deployment, usage of terrain, everything. From what the bird said, the governing Cerebrate seemed like it actually knew its business.
Anyway, that's all gone now. The zerg are all just ravening beasts that can mainly be found in former asari space and certain sections of the Traverse. I've heard reports of pockets holding out in the Koprulu Sector, but I know for a fact Char got cleared out and turned back into a lucrative mining colony. It's unlikely we will run into the fuckers.
Oh, there's also a significant number of the damn things on Tuchanka, thanks to the dangerous and nonsensical attempts of one Warlord Okeer to cure the Genophage using zerg tissue. Aside from the presence of infested vorcha basically anywhere in the Terminus Systems, that's about it for zerg territorial holdings. The geth, turians, protoss, and colonials burned them out of everywhere else.
Biology
This section ended up brief; anything of value on this subject was being snapped up by the turians and salarians. Put simply, every zerg lives out Charles Darwin's "best species is the one most adaptive to change" spiel by evolving on both an individual and species wide basis to combat common threats. As a result, all zerg are to some degree resistant to blunt trauma, lacerations, blood loss, and etcetera.
Two notable exceptions to this appear to be concentrated dosages of radiation and fire. The radiation apparently screws with their hyperadaptive cells and makes them die off stupid quickly, while the fire slips through the gaps in their armor and cooks the soft bits underneath. Thanks to the Great War, incendiary and polonium rounds are still issued to Council ground troops far more often than any other ammo type, and the Dominion still fields Firebats. The bugs made quite an impression.
All zerg are also capable of vibrating their muscles to dig themselves into little holes. It makes the bastards surprisingly hard to detect, and zerg ambushes from underground were a common feature in the Great War. For the poor fools venturing into ex-asari space in search of eezo… it's still commonplace there, too.
Zerg in the Athena Nebula all possess biotic ability, which mainly manifests itself through "pull," "barrier," and "warp" techniques. The Athena Nebula has become widely avoided for this reason.
It's worth noting (even though it has "infested" popular culture even here on Earth) that the zerg are capable of infecting other creatures with the Zerg Hyper-Evolutionary Virus. This usually manifests in skin rashes, impotence, and huge ass claws bursting out of the poor fucker's back… provided that the fucker in question is a human, salarian, turian, or batarian. Other races produce different results.
Zerg "Pure" Strains
Zergling: Probably still the most common type of zerg, even with the vorcha spreading like heinously ugly wildfire over in the Terminus Systems. These four-legged dog-lizard bastards breed at prodigious rates and move faster than my tenants when I say the rent is due. When the Swarm was still cohesive, they typically performed scouting roles or attacked in vast hordes, serving as cannon fodder to distract enemy forces from the more dangerous strains. Nowadays, they just act like those stupid fucking pitbulls from next door, indiscriminately reproducing and attacking anything in sight.
Hydralisk: The most photogenic zerg strain, if the salarian films were any indication. Think a cross between a crocodile, a praying mantis, and a snake, then give it the ability to spit gauss rounds with enough force to punch through battlecruiser armor. That's these guys in a nutshell. They're probably directly responsible for more military casualties in the Great War than any other land based strain, and that's saying something. They can take a beating, prefer to ambush from underground, and usually hunt in packs. They also weren't a terribly advanced strain, from the looks of things, as their numbers haven't really suffered after the Great War's end. If you're venturing into zerg territory, bring motion detectors. These fuckers don't give you second chances.
Drone: Look like big ugly wasps. They're clumsy and fat, so they prefer not to fight. They're responsible for growing zerg colonies, but nowadays usually cluster in isolated areas and get preyed on by zerglings. They're responsible for the zerg infrastructure, but now the Overmind Union's fallen through and they're all out of jobs. Not much of a threat, and in danger of going extinct. Good riddance.
Overlord: Threatening looking party balloons that float over the battlefield disgorging more threatening zerg strains. They're C+C organisms with transport capabilities, but have a hard time commanding or transporting the feral zerg these days. Apparently great herds of them have taken to wandering the stars, and occasionally crop up close to civilized planets. Usually they get destroyed, but I've heard sometimes people treat it like an event and take people up close to look at the things like they're fucking space whales or something. Guess it makes a certain kind of sense: they're harmless and they lost the war. I mean, I'd still shoot them, but whatever.
Mutalisk: Despite what salarian film directors might think, it was these evil ship-fuckers that did most of the damage in the Great War. Bearing great leathery wings and capable of either spewing steel-melting acid or shooting homing parasite projectiles out its rectum (I WISH I WAS FUCKING JOKING) the humble zerg mutalisk is capable of both space and atmospheric flight through a combination of what I can only assume is psionic energy and bullshit, because wings don't fucking work in space.
These freaks travel in enormous swarms and were typically the answer to terran siege tanks, interceding Council fleets, and supply lines. While they didn't terrorize the relay system like the scourge, their existence was a fucking nightmare as ground forces were frequently overwhelmed through sheer numbers and softened already by previous ground attacks, while the Council's primary ship armaments could not reliably hit the damn things, leaving the GARDIANs to pick up the slack.
Fortunately, mutalisks are fragile, and their wings are easily damaged. Towards the end of the Great War, both colonial and Council forces were aiming to the left and right of center mass, making the bodies hit the floor. Didn't do much to deter the main bulk of the shrieking fucknuts, but it least evened up the casualty count. These days, mutalisks are a rarity, but nests of them can still be found on Thessia and Tuchanka. I would advise not disturbing these nests.
Scourge: Suicide bombers. They were just flesh sacks loaded with vespene that got their jollies by ramming enemy ships and exploding with more force than my uncle's colon after eating too much corn. Not much to say, seeing as they're extinct. They used to nest on mass relays and fuck up anybody that came through, but those days are long gone. Without a driving intelligence to produce them, nature apparently got rid of them. No tears shed.
Queen: Extinct strain these days, appeared to be some kind of flying specialist. Got reports of them spitting out parasites that killed siege tank crews and then crawled out to attack anything nearby. It's unclear what exactly they did, though the presence of queens was generally noted to be a tip off for an incoming massive zerg attack. So, probably reconnaissance. Nature wasn't having any of that either.
Guardian: Part of the lovely two hit combo that knocked out many colonial settlements, guardians are an advanced strain that spat corrosive spores over great distances at ground targets. They couldn't do jack to defend themselves in the air, but they were usually surrounded by mutalisks and hydralisks, making this much less of a problem. They still exist today – barely – in small numbers around the aforementioned mutalisk nests. I strongly advise not disturbing these nests.
Defiler: The other part of the two hit combo, though this one is thankfully extinct. Looking like one of those bastard silverfish that scared the shit out of me as a kid, defilers were mainly responsible for screwing with Council and colonial targeting systems by coughing up these massive clouds of spores, letting the other ground zerg close the distance by using the cloud as cover. Guardians would typically eliminate long range defenses first, and then the defilers would deploy their cloud and let the rabble run on through. Thankfully, the fucking things were rare and thus, probably hard to make (grow, whatever.) Hence, their extinction.
Ultralisk: The advanced strain we all wish had gone extinct, and still hasn't. Standing about twenty feet tall at the shoulder and bearing a pair of monomolecular scythes on its wrists, the ultralisk is heavily armored, fast, and terminally angry. These things shrug off siege tank rounds, gauss rounds, and laser weaponry with impunity, although they were noted to have some trouble with biotics. Naturally, we don't have any biotics. Fortunately, these things are rare, only cropping up on worlds with major infestation (so, most of the Athena Nebula and parts of the Traverse) and their rampages are usually easy to avoid.
Apparently there was also some sort of super strain at the Battle of Thessia that was continually resurrected by Cerebrates after being mangled by the protoss. They called it a "torrasque," but if it existed it should be long dead by now.
Leviathan: Massive zerg flying organisms that have not been seen in years. They were responsible for carrying entire brood into battle, and engaged capital ships on a regular basis. They were basically zerg dreadnoughts, used to shatter the bigger enemy ships and terrorize the planetary populace below. They commonly took down enemy vessels by either physically pulling them apart or spraying a corrosive substance over the hull and melting it into slag within an instant. Dead now. Good riddance.
Hybrid Strains
Infested humans, turians, salarians, and batarians: Lumping them all together because they were all completely fucking useless for the most part. Turns out taking the guns away from humans, salarians, batarians, and turians kind of is a big "fuck you" to combat efficiency, and no amount of back mounted super talons is going to change that. For the latter two I found that biotic individuals manifested a slightly more impressive strain, but they were so fucking rare that there wasn't much to read about.
Infested asari (witches): Turns out giving the zerg biotics turns them from a deadly horde of space bugs to a skittering apocalypse. Witches look like asari with serrated nails and teeth, purple carapace instead of blue skin, and a horrible predilection for charging into battle using biotics, shattering the front lines. Despite possessing the ability to claw and bite their way through neosteel, they prefer to use biotics to strike, pulling foes over, warping their armor, or even using biotics to assist their punches and sending foes flying.
Witches are extremely aggressive and hunt in groups. They also, rather disturbingly, have the ability to issue limited commands to feral zerg, meaning encounters with them in the Athena Nebula are usually heralded by the arrival of a hydralisk ambush first. Avoid at all costs.
Infested volus (banelings, "rolly pollies," "rolly bastards"): Volus live in high pressure ammonia environments and tend to burst when their suits are ruptured outside their space, but that didn't deter the zerg from weaponizing the helpless fucks. The zerg encased them in a carapace and gave them a trigger mechanism to let the carapace split open. They also fed the stupid things vespene. In low pressure environments, banelings light the place up, and their usage was crucial in the initial stages of taking Thessia. They were used primarily to bust open fortifications and large numbers of troops. Being fat, fragile, and glowing a vibrant green, most banelings were usually unable to close the distance to enemy troops before detonating and making a mess of the zerg's back ranks. To compensate, they usually got carted around by overlords and were dropped directly on the heads of whoever was unfortunate enough to be fighting the zerg that day.
There don't seem to be many banelings around these days, probably because suicide bombing does not lend itself to reproduction opportunities, but all it would take to bring these guys back is for the zerg to somehow get their shit together and start another rampage. So… extinct, basically.
Infested elcor (Dekuunalisks, "lost ones,"): The most famous infested strain after the vorcha, dekuunalisks became a common sight after the elcor lost their homeworld. They are known for two things: firing massive spines in huge arcs at enemy forces, letting them serve as artillery for zerg forces, and their ability to speak. The translators adult elcor are all fitted with remained with them through infestation, and the sick Cerebrate that made them even saw fit to make sure next generation dekuunalisks somehow had the capacity for speech.
Their statements are generally prefaced with a "disgusting mockery" of elcor speech patterns such as "gurgling exclamation," "frenzied scream," and "enraged roar," followed by some declaration of an intent to kill their prey. Dekuunalisks are quite vocal in combat, and even in the back ranks their cries can be heard for some distance.
At medium and close range, dekuunalisks still possess the ability to fire spines, but do so at a lower rate as they have difficulty aiming. There have also been reports of them running down their foes and trampling them to death, but this generally only happened during routs. Dekuunalisks feature heavy armor and an astounding mix of durability and speed. They are also, unfortunately, one of the most common zerg breeds, and can be found throughout zerg space. Like the vorcha, it seems they were able to figure out reproduction without Cerebrate assistance. They easily outnumber actual elcor at this point.
Infested krogan (viscerators): Fortunately only found on Tuchanks, the viscerators are easily the most dangerous hybrid zerg strain (excusing maybe the witches) and were created through the idiocy of one Warlord Okeer. The brutes have staked out a large section of Tuchanka for themselves, and apparently commonly prey on Thresher Maws in addition to other local clans.
How to describe them… picture the resilience of the ultralisk, the adaptability of the vorcha, the sadism and intelligence of the hydralisk, and then give them fucking biotics because OF COURSE OKEER WANTED SPECIMENS FROM THESSIA FOR HIS EXPERIMENTS.
In battle, viscerators work as teams, usually leaving one or two to handle the ambush from underground while the others close the distance or begin a biotic attack. Like witches, they too possess a biotic charge and commonly enter battle with it. Their hides are thick and hard to penetrate with weapons fire, and viscerators frequently enter blood rage during combat, making them disturbingly difficult to take down, and all too prone to suffering hideous injury, falling over, and then getting right back up as their secondary nervous system is kickstarted.
One public domain Umojan report stated that a team witnessed a viscerator's wounds literally closing before their eyes, and that the entire battle was punctuated with what might have been laughter.
If there is a silver lining, it is that even the krogan clans are united in thinking these things are abominations to be purged, and four different clans are currently making headway into doing just that. The dark cloud on that silver lining is that the Genophage cure was, in fact, effective, so their numbers are only being kept in check by their own natural aggression and their continual skirmishes with Thresher Maws and the aforementioned tribes. Current viscerators are notably more vicious than the original strains thanks to the constant conflict. It might be best to just have Tuchanka destroyed at this point – sounds worse than New Jersey.
Infested vorcha (…vorcha): There are no unmodified vorcha anymore. Of all the races to be attacked by the zerg, the vorcha were the only species to adapt and then thrive off of the Hyper-Evolutionary Virus.
Unlike the rest of the strains, it is a near certainty we will run into these things. They populate the Terminus and Traverse systems in great numbers, and sometimes hire themselves out to the KMC. They are the closest the galaxy has seen and probably ever will see to "civilized" zerg. The extended lifespan granted by the zerg cells has, if anything, let the vorcha become more civilized than they were beforehand.
Unfortunately, all data on vorcha indicates that they vary widely in physical characteristics, as each is a product of the environment they live in. The only universal traits are a predilection towards violence as a means of communicating and solving problems, a weakness to fire, extreme regenerative capabilities, and the ability to reproduce like you wouldn't believe. Omega was apparently overrun by these things in a matter of months, and "pest control" is becoming increasingly difficult. Hell, if these things continue on the path they're on right now, we might see a (much slower) zerg invasion over the next few decades! Torch these things wherever you find them, Vice Admiral. They hire themselves out as mercenaries as a means of slowly colonizing the galaxy, I am sure of it.
Threat Level: Green
You chose a good time for your invasion, Vice Admiral. The zerg's planet munching days are done – if you really wanted to and were willing to spend the lives, you could probably render the zerg totally extinct barring the vorcha within three decades. I'm not opposed to it. Good hunting!
Captain,
Thank you for your efforts. Kindly never send anything to my desk again.
-Vice Admiral Alexei Stukov, Head of Special Projects Division