Thorne Sherman is the captain of a small supply boat sent to bring provisions to a lab on an isolated island. When he arrives, inclement weather prevents the offloading of provisions, and he finds the resident scientists nervously awaiting him with guns. Much conversation and beating around the bush ensues, until finally the truth comes out: The scientists have been performing experiments on overpopulation by genetically engineering shrews which grow to the size of sheep dogs, eat incessantly and breed profusely. These giant shrews have escaped and are overrunning the island, stripping it of food until the monsters must turn on the humans, trapping them in the small house/lab.
Unfortunately for the humans, the rains are weakening the house's adobe walls, allowing the Killer Shrews to burrow their way in. Although only a couple shrews actually make it inside, it's enough to kill a house servant and a lab researcher; the shrews also gobble up Thorne's sidekick Rook whilst attempting to bring items ashore from the boat. Realizing they can't stay in the house because the shrews are getting in, but can't go out of the house because the shrews are out there, Thorne gets creative and builds a portable tank out of empty oil drums. He, his Love Interest and her father the lead scientist all escape to the beach in this tank and finally ditch into the ocean and swim out to Thorne's boat (now safe, since shrews can't swim); but the last lab assistant panics and refuses to join them in their escape, and so gets himself eaten. The shrews are left trapped on the island, where it is assumed they will eventually starve and die off.
After decades of making jokes about doing it, Best starred in a 2012 sequel The Return of the Killer Shrews.
This film provides examples of:
- Artistic License Biology: Shrews can swim. They're also inclined to engage in cannibalism even when they haven't stripped their habitat of alternate prey, making them a poor choice of analog for experiments in human overpopulation.
- Artistic License Gun Safety: When the Mexican servant is bitten in the leg by a shrew, Thorne tries to stop the bleeding with a tourniquet. What does he use to tighten it? The barrel of his loaded revolver.
- Black Dude Dies First, and Mexican dude dies second.
- Closed Circle: The island. An imminent hurricane prevents a quick evacuation.
- Dirty Coward: Lab assistant Jerry.
- For Science!: The creation of the Killer Shrews was actually an experiment to study the effects of overpopulation, an experiment which has (everybody say it with me) Gone Horribly Right.
- Also, one of the scientists, when fatally bitten by a shrew, calmly records the progression of symptoms right up to the instance of his death, rather than say anything to all the people in the room with him.
- Giving Them the Strip: One of the girl's boots is torn off by a shrew, but she's not actually bitten.
- Island of Mystery: The island.
- Jerkass: Jerry.
- Karmic Death: Jerry, after repeatedly trying to feed the hero to the shrews, finally is taken down by them himself.
- MacGyvering: The solution to escaping from the house to the boat without getting bitten.
- Mad Scientist: Averted, surprisingly enough. Dr. Craigis may have accidentally created a pack of giant shrews as a side-effect of his experiments, but he gives a reasonable justification for everything he does and takes care from the beginning that nothing that he did could endanger anyone outside the island.
- Mad Scientist's Beautiful Daughter
- Minimalist Cast: Only 7 characters in the entire thing.
- Plucky Comic Relief: Rook, the hero's plucky sidekick (see also Black Dude Dies First)
- Rodents of Unusual Size: Shrews are sort of like rodents, although now all classified in different orders.
- Scare ChordSherman: How big do [the shrews] get?[chord]
- Slurpasaur: The eponymous shrews are played by dogs in very unconvincing masks.
- What the Hell Is That Accent?: Lampshaded by the heroine herself, who chides the hero for not even commenting on her unexplained accent.