District 9/WMG

Prawn color denote a caste system
Christopher and his "son" (they are asexual) are the only green Prawn. They are either leaders or engineer (or something like that) while the other Prawn are soldiers, workers, drone and the likes. Yellow/Wasp Prawn could be poisonous and indicate a warrior caste.
 * The prawn at the end that most assume was Wikus was also green. Which might explain why those prawns saved him, they recognized him as one of their leader caste.
 * This makes an awful lot of sense if you consider that Christopher's friend was yellow, a good fighter, very strong and really fast, which could signal he was his royal guard.
 * This troper believes that greens are Leaders, yellows are Guards, reds are Soldiers, and the rest of the colors (browns, blues and blacks) are Workers. Think about it; greens (Christopher, Oliver and Wikus) are smarter than the others, the only yellow with characterization (Paul) dies protecting a green, the prawn on 'warning sign' in the eviction montage has a red face painted on it, ...

Prawn society is much more complex and diverse than it looks
First of all, just because they have a hive mind doesnt mean they are mindless, like..the Zerg, Tyranids or Borg. Drone may be a little "dumb" but im sure they are not mindless. Its simply too complex and alien to be perfectly understood. They think for themselves AND receive direction from the hivemind, which ensure the cohesion of their society.
 * Hive society does not equal hive mind. The former is a social/reproductive pattern, the latter implies a uniformity of thought or an actual Psychic Link and does not really exist in nature.

The "fluid" is derived from the prawns themselves.
Probably to facilitate body disposal on intergalactic excursions. They've already shown a higher understanding of biotechnology than anything seen on Earth such as locking their weapons to only respond to their genetic code. It isn't much of a stretch imagining that knowledge applied in other ways. It would also explain how  from what is otherwise (essentially) rocket fuel. The reason the prawns don't try to synthesize more from their dead is that 1) they have moral issues with doing so, 2) the fluid's manufacturing technique is a secret even to the majority of aliens, or 3) they simply didn't have the right equipment.
 * Jossed via Word of God they're nanomachines that would fix the mothership
 * That makes perfect sense, as the first thing that begins to transform is Wikus' injured arm. Given that all of the alien technology seems to biological, then naturally prawn nanomachines could fix a person as easily as a spaceship.
 * Also would explain (partially) why Wikus began transforming to begin with. The fluid simply started to fix his injuried arm into the only biological entity it's familiar with.
 * Equally the nanomachines might have decided that Wikus was 'broken' and tried to 'fix' him...

The aliens were originally sent to Earth with the intent of forming a penal colony
Much like the British Empire did with Australia, the major powers on the prawn homeworld (or at least those from the region advanced enough to master space travel), decided the best way to deal with rising crime rates was to simply ship the bulk of criminals to a completely new planet. Either they weren't aware that Earth was already occupied by sentient beings or simply didn't care. The various alien weapons were meant to be used by the prison guards to keep order in the new colony, but at some point, whether out in space or in the intervening period between the ship's arrival on Earth and the first contact with humanity, the prisoners decided to revolt, ending in the deaths of most of the ship technicians and the more violent convicts. Most of the ones that survived to the present were the 'lesser' criminals; political dissidents, intellectuals, and the proverbial "bread thieves".
 * Word of God actually states they were colonists, and only landed on earth because the ship's auto piolet found it the only habitable planet in range.

Christopher and his son are the only surviving members of an Engineer Caste of aliens.
This is why he had the ship's control module buried under his house (he was trying to repair it at the time and crashed in it) and why these two aliens seem to be the only ones with more than catfood for brains.
 * There was an interview where Blomkamp revealed that the concept of the Prawn didn't come together until he thought of their caste system as more of a hive-mind that had lost its Queen. And just like in Real Life, the Prawns eventually spawn a new queen (Christopher).
 * Actually, since Christopher says he's been searching the junk for twenty years (ever since the ship came down), that implies he was full-grown (and not 'spawned') before District 9 was formed. Following that logic, since Christopher's 'son' seems just as intelligent as he is, it's actually more likely for Oliver (Olivia?) to become the new 'queen'.

Christopher is the Captain of the alien ship
He lived in the command section of the ship, which included a vehicle that functions both as the bridge and as a sort of "Captain's Yacht." At the beginning of the prawn exile on earth, he took advantage of the ensuing chaos and the fact that the "passengers" (more like sentient cargo) had never seen his face to go incognito as one of them. He had every intention of hanging everyone else (including Wikus, once he'd served his purpose) out to dry and returning to the homeworld with just himself and his family. However, breaking into the MNU lab and seeing with his own eyes the true plight of his people, he did a Heel Face Turn and acquired a sense of duty and honor.

Christopher and his son are transformed humans
Christopher and his son are green, just like Wikus was after his transformation. Perhaps he and his son came into contact with the fuel and became aliens. He soon began thinking of himself as part of the aliens, learning about their culture and technology and began planning to rescue "his people." This explains why he and his son are the only aliens that wear clothes, understand the human legal system, and why his son doesn't know how many moons are on his home planet. As for the "cure" for the fuel, Christopher might have been lying just to get Wikus to get him into the MNU facility and get the fuel.
 * Several of the other prawns in the film wear clothing, so it's hardly unique. His greater understanding of human rules could just be due to his greater intelligence and interest driving him to learn about them. And as for his son, well, the prawns had been on Earth for more then 20 years by that point. Chances are his son had been born on Earth.

The prawns, as a species, were created in a lab
As demonstrated by Wikus' transformation, the "fluid" is a genetically-engineered bio-agent that can make a prawn from any species with a suitable genetic codebase. This is further evidence by the fact that their method of reproduction requires a contrived method of providing external nourishment to their eggs.
 * The incubation chambers would seem more like an artificial womb, a substitute for the queen rather than any labratory grade equipment. The fluid has been revealed to be nanomachines.

The prawn homeworld is in the next solar system, or someplace similarly close
Recent studies suggest that any sort of communications signal known to human science gets lost in the galactic background noise after about one light-year, so it's entirely possible they've been there the whole time and we didn't know it. Considering how little fuel makes the difference between a three-year round trip and not moving at all, the prawns' method of interstellar travel provides only a slight advantage over subluminal travel. The ship that stopped over Joburg may actually have been their first attempt at interstellar travel. It would explain why no one from the homeworld has come after them, even though Christopher strongly implied that there's someone there to go back to.
 * Jossed. Visual cues in one scene near the end indicate that it's in an elliptical galaxy.
 * Also, current science actually says only that our normal commercial radio leakage get lost in noise, not "any sort of communications signal known to human science"; a sufficiently energetic and coherent beam would, in fact, punch through. That's why most plans for hypothetical interstellar probes feature a strong laser to communicate. The only reason we don't have a signalling device that could reach the near stars is that no one has ever bothered to spend the money to build one; the limit is budget and priority, not technology or physics.

The DNA lockout on prawn weaponry is a safety feature.
Prawn weaponry has been demonstrated to be extremely sophisticated, operating with almost surgical precision. Thus, it is most likely controlled, at least in part, by interfacing with the user's brain through the central nervous system. Since this would be calibrated to prawn neurology, and use by other species might very well cause the weapon to malfunction, for the sake of life and limb, the weapon is designed to make damn sure only the correct species can fire it.
 * Yes that was the point.
 * Maybe not; combining two other WMG's, if the Fluid is a nanotech designed to repair Organic Technology, and if the Prawns are not a natural species but the result of accidental Fluid exposure that remade them into biomechanical lifeforms, then maybe the tech only works because it recognizes them as other tech.

The aliens were once human-like creatures.
They created the fluid and used it as fuel for their ship. At some point, an accident occurred, and many or all of them were infected by the fluid, making them turn into prawns.
 * Two theories as to how this happened: Either they were purposely transformed by their mysteriously-absent overlords to serve as workers, or they were transformed by a fuel leak in the course of the incident that left their ship stranded. In the latter case, they completed their transformation over the three months that went by between the ship stopping and the humans cutting their way inside.
 * Alternatively, they were once Rubber Forehead Aliens in the distant past, but the fluid they used to power their technology permanently mutated the whole species into the bug-like forms they have now.

Catfood either makes the aliens stupid, or gives them a small amount of something that they need to be smart.
Being stuck on an alien world, with no access to their normal diet, the entire alien population is suffering from a severe vitamin deficiency that retards their intelligence. Catfood happens to contain trace amounts of the stuff, or something like it, but nowhere near enough to actually solve the problem. Christopher had access to vitamin supplements. Alternatively, the catfood is Instant Maple and Ginger Oatmeal, and Christopher and his son Just Say No.

The aliens and humans share a common ancestor.
This is why the fluid is able to alter humans so dramatically.

H. P. Lovecraft encountered one of the aliens prior to their arrival on Earth.
They went on to become the basis for the Cthulhu Mythos.

Wikus was set up to fail
Seriously, who puts a hapless romantic bumbler who makes paper-mache bowls for his wife in charge of a military resettlement operation? Against super-strong aliens with insane weapons technology? Seems like a recipe for one dead bumbling bureaucrat, to me. Unless Wikus' father-in-law wanted him dead, for whatever reason...
 * Not a WMG, it's pretty clearly canon.
 * It's pretty clear from the way his father-in-law acts that he's one of those creepy overprotective fathers who wants their daughter to stay single and got his son-in-law a job where he was likely to be killed. Is that a trope yet? Because this is like the third or fourth time I've seen it
 * Combination of Overprotective Dad and The Uriah Gambit.

The reason for the Prawn's social problems aren't based on any caste system, but are economic in origin
It fits the whole racism allegory better - the reason the other Prawns seem to be so listless is due to their new environment. They're hungry, they're lost, frightened, homeless, malnourished, and living on a planet where they're treated like dirt - dirt that you can eat to gain magical powers. They have no educational or autonomous governmental infrastructure. The whole 'they are unambitious and beaten-down because they're part of the worker caste' is just a canard to put a stop to humanity's guilt over the whole situation. Christopher and his son were just geniuses, not on a higher caste level, but just on the good side of the bell curve.
 * Part of this depends on how long a prawn lifespan is, though.
 * Note that this theory is exactly the same as what happens to humans in the same conditions. This movie is a even more depressing when you look at it as the Anvilicious allegory for racism/xenophobia/prejudice in general that it is, and realise that it's absolutely spot on.

The Prawns find a better home in District 10
This has appeared in the main article enough that a number of people must believe it. This Troper thinks it to be wishful thinking, but it's quite possible that they manage to find a reasonable standard of living before the Nigerians (or other corrupt humans) move in again due to Nature abhorring a vacuum.
 * Or, as a more likely alternative: Alien Auschwitz.
 * Looks like you kinda missed the end-notes about MNU coming down hard for crimes against humanity, no longer being in control (the main reason of the move is another nicer Megacorp is taking over) and D10 population being 2.5 million and growing (making it fairly clear their reproduction isn't being controlled).
 * For the time being... (But yeah, I forgot about that.)
 * Well seeing how the whole thing is based on apartheid with an anti-apartheid message at that, D10 becoming a death camp would make it a Broken Aesop, so the sequel would be about humans and prawns putting their past behind and working together.
 * True, but we could get a sequel along the lines of Inglourious Prawns if Christopher comes back to a Holocaust parallel. Just sayin'...
 * And I figured the sequel would be more like Independence Day, but the aliens have firewalls.
 * Which both would be massive Disproportionate Retribution because its only MNU fualt, and again, a Broken Aesop.
 * It's even more of a Broken Aesope if you act like it's only MNU's fault. Racism is never one company/institution/government's fault. It's insidious and a part of the population's attitudes. The worst kind of racism is the subtle, unconscious, unquestioned racism.
 * Don't hate me, but "all men are created equal", and the Prawns are big over-evolved bugs. Even if you can somehow argue (to the satisfaction of the general population) that aliens deserve human rights in the first place, you can tell why the natural human reaction is not to welcome them with open arms. Hell, at least in fiction-South Africa we give them a home, however bad the conditions. In the fictional versions of some other countries I might mention, aliens get dissected. Say what you like, but at least the Prawns are still, yanno, alive. For historical parallels, just think back on what happened to the native inhabitants of America, and know that the wholesale slaughter of the original locals is one thing that didn't happen in South Africa.

Ozymandias created the prawns
Assuming the public mood in the pre-alien Disctrict9 verse is anything like it would be in our world, apartheid is made illegal, but the issue is still being settled in the streets. The prawns show up, and extremely quickly blacks and whites alike are fighting side by side against this new threat. Sound like any entrepreneurial super villain and his giant squid that you know?

The Alien Homeworld doesn't care about what the humans did to the ones in D9

 * This is more about if they're a true Hive Mind, but like the Bugger the race as a whole really doesn't see a million drones being treated like crap a big deal (this explanation would make them just as bad as humans)
 * Or possibly didn't- they probably don't have any idea what happened to the Prawns on earth, if they were even still alive. Once CJ gets back with stories to tell, though...

The title is a Shout-Out to Plan 9 from Outer Space.
Really, it could be any number, not necessarily 0-9 either.
 * I took the 9 to be a flipped 6, for District Six in Cape Town, where 60,000 people were forcefully removed from their homes by the Apartheid regime.
 * Aye, I'm pretty sure that's what it's referring to...I think Blomkamp may have said so explicitley at some point, though I can't verify it. And really, if he was going to do a Shout-Out, why in God's name would it be to that movie?

The prawns' language is partially telepathic.
This explains how humans understand their unorthodox language so easily: the multitude of clicks and squawks produced by the prawns resonate at a frequency that, when heard, cause one's brain to "see" the words in a synesthesia-like manner. Those subtitles in the movie? They weren't edited in- Your mind makes them.
 * Why does the English subtitle still appear when the film is shown in non-English-speaking countries?
 * They've had twenty years to learn the prawn language. And South Africans would be used to languages with clicks and gutterals.
 * And when Wickus is told  he asks if he heard the last click correctly. If there was a telepathic aspect then he wouldn't need clarification on what "Christopher" said.
 * Then again, he may have asked for clarification out of sheer disbelief. Admit it, you've done the same; you've said "Did I hear that right?" when you know perfectly well you did. You just hope you didn't.

The film is set in the Warhammer 40,000 Universe.
Some time during the 41st Millenium, a Tau exploration ship gets sucked into a warp storm and teleported millions of years back in time. The warp jump kills the ship's systems, and the physically weak Tau soon perish, although some of their technology (battlesuits, plasma weapons) remains intact. The Kroot, after eating Earth insects, become the 'prawn'. The Nigerian gangs have seen the kroot's transformation through eating, and attempt to replicate it. Christopher is a Shaper, and if he successfully returns to the 41st millenium will bring the might of the Tau Empire down on Earth.

This will lead to Earth becoming part of the Tau Empire, causing a rebellion led by a man known as 'the Emperor'. How's that for a WMG?


 * There are more practical evidence for this. Firstly, the fact that the aliens in question could be said to resemble Vespids without wings-perhaps some twisted mutations (just look at this). Secondly, the power armour that has a near-replica armament layout and toughness of a Tau battle suit (somewhere between a XV81 and a XV9). Thirdly, the fact that the damn ship actually looks like a miniaturized carbon copy of Tau air caste space stations (compare this and this). Fourthly, the bar codes on the side of their heads resembling Tau writing. Finally, the alien's lack of decision seemingly pointing to a link between them and the now dead Ethereal. The Imperial Inquisition thanks the above troper for the alert...


 * Why does every single WMG need a Warhammer 40K section?


 * For the same reason that every single WMG needs a Time Lord section. By now it's just status quo.

The prawns are Decapodians or a related species
Crustacean like aliens who enjoy eating just about anything, especially stuff like catfood. The Decapodians were established in Futurama as being one of the first species to contact humans, although in this case, they arrived much earlier. When Christopher comes back to liberate his people, they'll probably end up consuming a massive amount of the anchovy population while there.

The prawns are the Glorft.
When word of their treatment reaches back to the prawn homeworld, their military forces arrive on earth and engage in a fullscale assault, eventually conquering the planet by the early third millennial. The remaining human army steal a prototype prawn mecha and reprogram it to allow them to access it, then plan to send it back in time to the turning point of the war, however a malfunction sends it further back than intended.

The prawns are a collective of many different species, all of whome were affected by that fuel. And their form is best suited for interstellar travel.

 * There were several different colors of them. It's also implied they are not a natural species, given what Wilkus goes through. It's possible that they are an empire or federation of sorts, and the insect form is simply best suited to alien environments. The prawns are very strong and acrobatic, their hardened skin supplies a natural armor of sorts, and those feline eyes are probably suits for darkness. Christopher said there's technology that could change Wilkus back. Why would they have that unless such transformations occur on a regular basis? My guess is they get turned into the prawn form when they go abroad, and when it's time to come home, they are changed back into whatever they were beforehand.
 * Or they could be into body art and consistently paint themselves.
 * No, im sure the chitin coloration is either a caste thing or simply ethnic (much like the variations in human appearance).
 * Maybe, maybe not. It's not explained in the film.

The prawns were prisoners of another species.
They were found trapped inside the ship with little food or supplies without any kind of leadership. The reason being that they were prisoners deliberately left to die on earth. The ship was filled with their technology, which their captors dubbed useless, then they were sent to a random planet by an automated control system, said control system then detatched itself from the main craft so that they could not turn it into a manual control (the prawns seem to be very good at messing with technology) obviously Christopher found the control system anyway, converted it into a manual control system and plans to use the ship to fight off the evil aliens that left him and his race to die on earth.
 * What are the evil aliens though, Combine?
 * That's it! The prawns are vortigaunts! The prawn weapons don't work with humans because they need to be powered by a vort's energy.

The film takes place in the same universe as the misadventures of the Trix rabbit.
Just as the humans keep the prawn in line with their addiction to cat food, they also keep the rabbits in line with their addiction to Trix.
 * Win.

The Mother Ship was an invasion ship
Just look at all the stray weapons the aliens are selling not twenty years after arriving, which apparently MNU did not manage to confiscate as they ferried them from the Mother Ship to Earth. All things considered, they must have had enough weapons to occupy Africa before arriving. Only the lack of demonstrated weapons, defenses and dropships on the Mother Ship itself imply it had another purpose. Even if they weren't expressly military, whether it was a mining, research, exploration or production ship, those were a lot of weapons. So, is space full of space pirate they have to fight, do they have gladiatorial Death Ray matches, or do they have a lot of internal policing to do? That's why they played the "stranded ship without any command and stuffed with scared, seek, aimless drones" card! To shake off suspisions and make people neglect them (they are useless, near-animalistic and generally dissapointing), to make an excuse for moving them to the ground (they are sick, hungry and helpless), to buy them time for collecting intelligence (they have no way of leaving). This way they wouldn't need to drop the landing troops during the actual invasion. The landing troops are already there! Adapted to the enviroment, familiar with the combat potential of the enemy, waitng for the signal to become the "fifth column". Oh boy, I just hope they have some Nukes armed and aimed at the D10.
 * I'd say not invasion per se, for invasion is ahead still, but a reconnaissance and landing ship. That's why they chose Africa - the most depraved and out of control continent (no offence, Africans) would be perfect jumping-off ground.
 * Offense taken. Why would they come to South Africa, anyway, if that were the case? You know, ... one of the most advanced countries in Africa (along with others like Nigeria, ironically)? And in Johannesburg, of all cities? I know what foreigners think of the place, but around Jo'burg and Pretoria side, we're about at the same level of development as Louisiana and Mississippi. Which, I'll grant you, isn't much, but it's not exactly an anarchistic hell-hole.
 * Well, excuse me, but that's the way it was portrayed.
 * Dude, television lies.
 * To round off the argument here, I'm fairly sure experts in the movie theorize that Africa has a climate that makes the most sense to them (although I know that South Africa's pretty varied geographically, it's odd that they would choose a relatively arid region otherwise).
 * That would kind of fuck up the whole message of the film. "That which is different is threatening after all! Nuke 'em!"
 * Welcome to the real world.
 * Actual explorers tended to be well armed in case the wherever they ended up had natives hostile to foreigners, animals that where pretty damn tough or just so that if they ran out of food they could hunt.
 * Fuck up...or rectify?
 * Rectify? In a movie about apartheid... yeah...
 * The Aliens are NOT heavlily armed by any means. Please consider: 1) their spaceship itself, if used as a weapon and crashed into earth, can wipe out the entire human civilization. In comparison, their guns and mechs mere peashooters; 2) They have a population of 1 million. If 1 out of 100 aliens had a gun, then they already have TEN THOUSAND guns. How many militaries do you know that gives 1 gun to 100 people? Lastly, if you think "they had enough weapons to occupy Africa before arriving", you vastly under-estimate the combined military might of Africa. 1 million infantrymen is NOT enough to take over africa (maybe if the mothership was a warship, or if it had a fleet of fighter aircraft in it's hangers, but there is "the lack of demonstrated weapons, defenses and dropships on the Mother Ship itself").

The Prawns eat cat food for the Taurine.
Taurine is either addictive to them or they require a diet high in it. Cats can't create Taurine and need larger-than-normal amounts of it in their diet, so in the absence of energy drinks or the biological knowledge to extract it from animals, cat food it the best source.
 * This troper just imagined the promo spot for new "Powerbolt" soda, featuring a Nike-clad prawn leaping in slow-motion from the half-court line to slam-dunk a basketball and the caption:

Christopher lied to Wikus about the possibility of reversing his transformation.
That the black fluid didn't kill him outright is surprising enough; that its effects could be undone three years hence would be little short of miraculous. Christopher has also demonstrated his willingness to be... economical with the truth, if it's in a good cause, and Wikus was more use to him the right side of a Despair Event Horizon.
 * Actually he had the aparatus in the mothership,but Wikus saw that they couldn't get inside of it without cover so he choose of his on will to stay and give a chance to Christopher to go to his home,and when Christopher said he would come back wasn't to cure him but to free him of hellhole he was,so yeah he won't be able to come back to human life but he and Christpher already knew that when they escaped.

The "prawn" shown in the final shot is not Wikus.
It was a friend of his who ritualistically injured its arm to match his own in a sort of promissory "I will complete your dying wish, my limb is your limb and you can live on in me until we complete this" thing.

Exposure to gasoline would turn prawns into humans.
It's not that the alien fuel has random unusual transformative properties. That's just how things work in the District 9 universe.

Cat food has no special effects on alien biology.
They eat it because they're destitute and it's pretty much the only thing the humans are willing to give them (or sell them at an astronomical markup.) The idea that it does something for them is a rationalization conceived by the humans doing the selling, to justify their actions.
 * No, they're seen eating other things, mostly cow heads, and some references to eating tires from cars.
 * Doesn't mean that they have the required nutrients. There are numerous cases of pregnant women eating dirt (any other usual things) due to having nutrient deficient diets. Who's to say chewing on tires isn't the same equivalent or just mindless crap made up by the news.

The liquid is nanites like in The Empty Child/The Doctor Dances
Extra material says the liquid includes nanotechnology to fix the ship. It is also programmmed to heal Prawns, and when in contact with Wikus, assumes it needs to fix his body big time.
 * Isn't there a mention somewhere in the early Mockumentary part of the film that Prawn tech is partly organic? The Fluid "heals" the machines too.
 * Which leads to the possible corollary that the reason the Fluid turns lifeforms into Prawns is not intentional, it sees biological organisms as malfunctioning biotechnology and tries to "repair" them to perform whatever task it "thinks" they're designed for-- manual labor, most likely, judging by the strength of the Prawns.


 * And thus returns the status quo mentioned in the Warhammer 40,000 entry. Lolsocks.

The Fluid made the Prawns stupid.
The crew was originally smart—a Fluid leak not only turned them all into prawns, it made their brains too sluggish to repair their own vessel; The Mind Is the Plaything of The Body, after all. Only the brightest genius on board, "Christopher Johnson", was able to retain enough intellect to repair the command module. There never was a hive structure, the entire crew was the "smart class"... until they weren't.
 * It's also possible that Christopher wasn't a genius before; the effect of the fluid is starting to wear off, and his is the first intelligence to return. In a few years District 10 is going to be a very interesting place...

Prawns are a previously unknown form of The Flood.
Firstly, the "pets" look incredibly similar to the infection form, just with additional tail stingers. The prawns are the combat form, which has corrupted some unmet form of alien (the general colour scheme was retained, but somewhat dulled, much like the elite-based flood in the later games. For some reason the gravemind and carrier forms aboard the ship were destroyed, leaving them aimless and without their usual desire to infect (plus with only a few infection forms, all of which were kept away from humans they didn't have much chance). Therefore, they realised they were supposed to do something but didn't know exactly what, leading the the violence mentioned in news reports. The liquid is made from the infection forms, explaining why it causes such changes. Christopher is a rare mutation that allows some individual thought. After Christopher rescues the remaining prawns, the leftover technology is researched, giving humans intersteller travel (but the energy weapons remain useless). By the time of Halo, no-one thinks to equate the period of 20-odd years where aliens inhabited earth over half a millenia ago with the flood.

District 9 is a prequel to Bad Taste.
When Christopher returns to his homeworld, the government is unwilling to rescue his people, and the only ones willing to take any action against the evil humans are the fast-food corporations, who launch a small-scale guerilla invasion of Earth to exact revenge upon the oppressors, using the excuse of a food harvesting mission to fool their government. Alternately...

District 9 is a sequel to Bad Taste.
The alien vessel is a factory/processing ship sort of like the ones used to tend fishing trawlers, and was intended to capture, process, prepare, and store large quantities of food. It was even loaded with extra defensive weaponry in light of what happened to the last group they sent in.

District 9 is a prequel to Ender's Game
The aliens are actually buggers/Formics and are a reconnaissance group sent out before the first invasion. Acutally many thing point into this direction, mainly the theory that they are drones. Christopher comes back with an army and declares war on humans, and thus, the First Formic War takes place. Prawn is just another word for bugger. And honestly, except the wings, prawns are pretty much Buggers. But hey, maybe they EVOLVE wing in a short time. They maybe can't use wings on earth and therefore haven't been seen using them. WMG at its best.

The fluid, once it turns you into a prawn, makes you go insane.
Come on! Your human mind (Well, I just eating, time to read a book) is currently battling the growing prawn mind (CLICK CLICKITY CLICK CLICK!) and your body is currently changing into something that doesn't even resemble your human form. Around the time of the interviews, Wikus has now gone completely raving mad, and cannot remember what is was like as a human, except the memory of his wife, which is why he made her the metal flower. Poor Wikus, once he gets healed, he'll be so far gone his mind would get worse, mainly because the exact thing is happening to him, except in reverse (Prawn mind meets human body).

District 9 is a prequel to Avatar
Immediately following the events of the film, RDA (a rival corporation to MNU) was dispatched to pick up the pieces and try and get some good press for the D10 project. However, their investigations revealed that the "fluid" was actually a biologically processed form of an alien mineral that happened to be on a nearby planet. In addition to this, a lot of Prawn tech was confiscated and (sucessfully) reverse engineered to create military technology (such as the AMP suits.)

The Prawn mining ship was actually trying to reach Pandora when it malfunctioned and brought them to Earth. This is also why the Na'vi did not seem to have any kind of fear/xenophobia about the humans arriving on their planet- they had already seen another race visit to mine. However, the Prawns (with their advanced technology and kinder demeanor) didn't have as much of an impact on the environment as did the humans. It's quite possible that the Prawns opened up successful diplomatic negotiations with them and managed to get some to peacefully relocate.
 * Or, in a more entertaining and canocally accurate event, the Na'vi attack the Prawns at sight, begining a war between them. Think about it, the Na'vi killed the humans on sight at first, and they look a lot like each other, and with the Na'vi being the xenophobic bastards that they are, They would want to kill the Prawns, not giving a chance at diplomacy. The Prawns thoroughly pissed at this, they declare war. The vain and confident Na'vi think they can take them on like the humans. The Na'vi are extinct in a matter of hours. The Prawns share the unobtanium with the humans, finally making peace between the two and saving the human race.
 * Alternatively, both the prawns and the Na'vi decide they've been being kicked around by the humans too long and gang up on attacking Earth.

2012 will be caused by the returning aliens
Christopher said he will return in three years time (in travel time since his planet takes three years to go to and get back from) and the movie was in 2009. Seems like the prophecy will entitle ass kicking aliens that may cause planetary destruction.
 * Except that actual Mayans say there's no "prophecy", the end of one calendar just triggers a rollover into the next one's year-zero.
 * And the movie is set in 2002. The aliens landed in 1982 and have been around for about two decades when the audience meets Wickus.
 * 2010, explicitly stated. The narration as the ship leaves states "The ship is moving for the first time in 28 years". A three year return would be 2013.

The small pit-fighting alien bugs are newborn Prawns.
They go through a pupal stage, and emerge as humanoid miniatures of the adults like CJ junior. Which leads to a corrolary WMG, that the humanoid form is adopted as protective camouflage; during this pupal transformation they attempt to emulate the shape of the local dominant lifeform, at least enough to trigger some social-animal empathy (not a notably successful strategy in this case); expressive eyes, same number and layout of limbs, head on top, etc.
 * However as soon as the humans cut into the mothership the footage shows that the adults are already in humaniod form.
 * It could be a side effect of the aliens hive-mind telepathy. They're able to tap into a planets morphic-field, an automatic body process(like breathing or digesting food) then transforms them into a similar form to whatever pings the strongest morphic resonance and is therefore the dominant species. Also considering Wilkus changed-species in a few days three months would be long enough to change body shape.

The Prawns don't eat cat food; something in it is a necessary ingredient for making the nano-Fluid.
They just store it in an internal pouch for later use.

Humanity is less than a century away from Vichy Earth.
What happens to a dream deferred...

Christopher and his friend...
... were actually a couple they both parented Christopher's son.
 * This would make sense as the prawns don't seem to have genders.
 * If this were so, Christopher's son would not have said "Where's your friend?" but the far more poignant "Where's Mom?"
 * Or, Christopher carried Oliver, but Paul did a disappearing act when he found out. Several years later, he came back and asked if he could be part of his son's life again. Christopher being Christopher, let him in for a trial period, in which he helped with the fuel collection and took the risk of having the lab in his home. Then the MNU showed up with an eviction noticed and it all went wrong.
 * Could be that they were a couple, just not for that long. This troper referred to her mum's boyfriend as 'her friend' until he'd been around long enough to become a permanent fixture. And before someone says that they'd been working together for 20 years, Paul shows signs of being new at what they're doing. So Paul helping out is kinda like him taking an interest in his partner's hobby, but sucking at it.

The ship came to Africa deliberately to find people to convert into Prawns.
Africa is full of the poor and disposessed. The alien ruling caste sent the ship there to convert more people into workers, but lack the ability and/or desire to convert the entire population, so they figured the best way to do it would be to find a place with a lot of people nobody would miss.
 * Geez, thanks! I sure feel special now... *is African* Call me crazy, but I like to imagine the rest of the human race would care if aliens land and start creating an invasion force by turning people into more of themselves, whether their victims were African or not. Then again, judging by how involved y'all are when you need to help us out rather than strip-mine our favorite continent, maybe the rest of humanity not giving a sh** if we all die is a realistic scenario...
 * Mr President aliens have invaded and attacked - OH God what do we do, Defcon 1 people - let me finish, they've attacked Africa and seem to be leaving. - Oh well in that case organise a couple of concerts. Seems like a fair assessment, I'm sure a lot of people would care, at first. While the news is all over it and people would talk about it but generally speaking people are rather selfish. Perhaps we need to be to be able to function.

The ship uses an Infinite Improbility Drive.
That's how Wikus' transformation happened. Transformation is a fairly common side effect of the stuff.

The prawns home planet is called Golgafrinch.
The prawns who arrived on Earth were so starved and generally useless because they weren't colonists at all, they were really all the Telephone Handser Sanitisers, Insurance Salesmen, Public Relations Executives etc which the prawn didn't want on their home planet.
 * The Golgafrincham arrived on Earth two million years ago, so... no.

There is a third species out there, and the Prawns are at war with them.
The Prawn ship has powerful weapons that only work for Prawns, and no other species. Why else would you give such firepower to colonist, like a nuclear grenade launcher?

James Cameron's Avatar is an Alternate Future of District 9.
Note: Not just an expanded version of the "District 9 is a prequel of Avatar" guess above. In the District 9 timeline, the poleepkwa/prawns/formica stay in their ship, and the government has enough time to organize a group and resources to "study" them before sticking a can opener in the ship. In the Avatar timeline, they try to leave the ship for help as soon as they arrive, the humans neutralize them, find a couple of inhabited planets on the charts, and head for the nearest one. When they get there (or partway there), they find that the phluid couldn't get them back home, and only barely got them to Pandora. They find that the ships recognize the local Green Rocks that were kicked up by the crash as an alternative fuel source, head back to Earth at a slowed rate, then return once they've adapted the technology to run more efficiently on Unobtanium (still not as quick or efficient as the fluid, though) and drill for more space-oil. The humans don't care who they harm because they learned back in the 1980s that killing xenospecies for their resources results in consequence-free profit. Unfortunately for the Earth-Pandoran press, the Na'vi were too pretty to pin as a demonic race of human-eating, Exclusively Evil pests.

The Prawns are related, but not closely, to Xenomorphs.
They have similar insect-looking body structures, have language unpronoucable to humans, have no genders (they are both hermaprites.) The prawns could be refugees from the planet both them and Xenomorphs originate from, after attacks from the Xenomorphs. The reason they were in such a state at the start of the film is because they left quickly and without suppilies. The weapons they have were designed to fight them, which is why they really go for it.

The Prawns are converted human slaves being deposited back on Earth
For years, the aliens would come to Earth and abduct humans, using a bio-compound to turn them into controllable insect-like slaves. The bio-compound is so chemically rich that they also burn it in their ships for fuel. The converted human slaves, however, just weren't working right, so their masters put them on a cargo ship and had it programmed to go back to Earth and strand itself. Their memories of the home planet are the result of brainwashing to conceal their origin. Christopher's son was his actual son, a child, and has not grown since being converted. The masters did not kiil the slaves because that is illegal in their world.

The Prawn weaponry in the movie is just the equivalent of a gun locker and some exploratory weapons
The real guns and mechs that the Prawn army has are fuckin' terrifying.
 * That is disturbingly (and awesomely) plausible. Not to mention that the Prawns had to build those guns themselves while on Earth. That gun that shoot lightning that makes you explode? The Prawns built that in a slum. With a BOX OF SCRAPS!!! When the Prawn army arrives the humans are gonna be totally screwed.
 * Completely agreed. A space fairing civilization should have much better weapons than mechs and rifles. We've only seen their jeeps and hunting shotguns. If and when they decided to whip out their F22s, we are going to cry!

Prawn children of the Worker or Engineer castes like candy
Presumably, like the way a queen bee has royal jelly as opposed to regular honey, the Prawns of lower classes have simple food, while the Leader caste has higher quality stuff, whatever that may be. Prawn children of lower classes eat a kind of hardened sugar water solution, remarkably similar to hard candy, which is why Wikus thought that Christopher Jr. would take the candy. However, as Leader castes eat much higher quality food (gourmet sugar water, so to speak), Christopher Jr. didn't want it. In essence, he threw the candy in Wikus' face because, by giving him food for lower, "stupider" classes, because Wikus had offended him.
 * Or perhaps it was because Oliver didn't have the proper mouthparts to eat the candy. Their madibles are used to tear and swallow food like most predators, and Oliver would have likely choked on the candy when trying to eat it.
 * Or building on the original theory, Oliver is older than he looks and giving him the candy is offensive for a totally different reason. Imagine giving a ten-year-old a dummy.

MNU is a division of Reliable Excavation and Demolition...
And RDA is a division of Builders League United.

The prawns are Space Pirates
Specifically, the Zebesian species that serves as the Space Pirate's mook army. Aside from the obvious point ( They're both insectile humanoids of large but slender stature, with significant physical acuity), consider: Zebesian pirates are described as "almost feral," and are generally completely useless and ineffectual without a leader like Ridley or Mother Brain to guide their actions. Space Pirates have always been incredibly mysterious in the Metroid 'verse, and they are said to have been a dangerous presence even at the earliest points in Galactic federation history.

what happened to the District 9 group is as such: Their ship was traveling through space and tried to raid an alien vessel or Fortification, but underestimated their target. In the attack, their leader-figure was mortally wounded, surviving long enough to send the ship on a retreat course, but dying before it could finalize the navigation systems. Since the entirety of the crew was Zebesian mooks, noone on board was capable of using the system to return to Space-Pirate territory, and they just waited on the ship as it followed an autopilot to the nearest habitable planet. This took much longer than intended, and the ship was damaged enough that it couldn't support the massive crew on board.

The reason Christopher is more intelligent than the other prawns/zebesians is that he's a higher-level "sub-leader" caste, like the tougher Zebesian mooks that Samus fights in later parts of the game. (there's actually a type of Zebesian in super metroid that's green and resistant to everything except missiles, so the color scheme even fits!) He's smarter than the other Prawns/Zebesians because his type of Zebesian is intended to lead small groups, but he wasn't trusted with enough responsibility to actually control the ship. The reason he can do it in the movie is that he's spent all of his time repairing the command module and teaching himself how to use it.

The reason why the prawns didn't have any leaders is not because of malnourishment.
If supplies were running low the leaders could order the other prawns to gather the necessary food. However Christopher's faction mutanied against the other leaders' factions when they were still in space. He then brought the mothership over to Earth and dropped the command module miniship onto the ground so he could escape the chaos of the leaderless factions. Without any leaders at all the food and other resources were not rationed and so when the humans cut into the mothership they found many malnourished prawns.

The non-Mockumentary scenes were actually a dramatic reenactment made for the mockumentary.
The Wikus we see is not the real Wikus, and the ending was slightly candy-coated to hide the complete eradication of the prawn colony (Wikus included) at the hands of the human race.
 * THEY KNOW

The arrival of the prawn to Earth paved the way for Dead Space
We silly humans doubted alien existents until the prawn arrived. Many years into the future (enough for some planets to be prohibited) a young engineer gets a message from a ship near by....

The fluid is the black oil, or related to/derived from it.
Black fluid that turns people into another species and has some connection with that species' technology? Where have we seen this before? The prawns are either the original creators of the black oil, which was then appropriated by the Colonists, or one of the many races in the universe which have been taken over by the black oil, or one of the races making up the Colonists, which was implied to be a group of several species of which only The Greys were shown, or some kind of genetically modified warrior race created by The Greys.

The Prawns lost a war against a rival species on their home planet.
This would explain why their weapons are designed only to work for their own species.

Poleepkwan scientists are...

 * Crazy Prepared.
 * In love with really big guns.
 * Mentally hardwired to provide overkill.
 * Really big drama-queens who over-react, a lot.