In the docu-style, sci-fi thriller “District 9,” which arrives in theaters Aug. 14, hundreds of thousands of aliens become stranded in South Africa after their massive spaceship comes to a standstill above downtown Johannesburg. Unable to fix the craft, this massive population of tentacle-waving, exoskeleton-sheathed aliens eventually outstays its welcome; they become reviled by humans for burdening the country’s welfare system even though all they really want to do is go home. Corralled into District 9 — a rubbish-strewn refugee camp that calls to mind Mumbai’s septic squalor, captured to striking effect in “Slumdog Millionaire” — they are segregated from the general populace by barbed wire. There, the film’s sentient yet excitable aliens are denied such basic necessities as running water and are denigrated by native earthlings as “prawns” for their resemblance to Sasquatch-sized shellfish. More..