Venomous spiders get exposed to a noxious chemical that causes them to grow to monumental proportions.
After a long absence, Chris McCormick returns to his quiet hometown of Prosperity, Arizona, to reopen his late father's mines. However, a chemical spill and lethal toxic waste have created an unstoppable army of giant spiders who prey on the unsuspecting locals, turning Prosperity into an endless buffet. Now, it's up to Chris; Sheriff Sam Parker; her son Mike; Sam's plucky daughter, Ashley; the conspiracy theorist, Harlan, and a handful of survivors to stop the hairy menace, and save the town. But, who can stand in the way of the disgusting eight-legged freaks?—Nick Riganas
In Prosperity, Arizona, a toxic waste barrel falls off a truck in a creek. The spider collector Joshua "Joss" Taft feeds his spiders with crickets from the creek and notes that they are growing in a high rate. The boy Mike Parker, who loves to learn about arachnids, visits Joss and he shows his big spiders. When Mike leaves Joss, one spider escapes from the aquarium and attacks Joss, who accidentally breaks the other aquariums during the attack. Meanwhile, Chris McCormick returns to Prosperity after leaving the town ten years ago and is welcomed by his aunt Gladys. Chris is in unrequited love with Sheriff Samantha "Sam" Parker and left Prosperity after punching her ex-husband. The town is now decadent since the gold mines that belonged to his father are closed, and Chris intends to reopen the mines. When Mike sneaks out to visit Joshua, he finds a big spider leg and web, but nobody gives credit to the word of the boy. Out of the blue, the spiders attack Prosperity and the residents must defend themselves under the leadership of Chris and Sam.—Claudio Carvalho, Rio de Janeiro, Brazil
The residents of a rural mining town discover that an unfortunate chemical spill has caused hundreds of little spiders to mutate overnight to the size of SUVs. It's then up to mining engineer Chris McCormack and Sheriff Sam Parker to mobilize an eclectic group of townspeople, including the Sheriff's young son, Mike, her daughter, Ashley, and paranoid radio announcer Harlan, into battle against the bloodthirsty eight-legged beasts.—Sujit R. Varma
In the quiet mining town of Prosperity, Arizona, an accident involving a rabbit causes a barrel of toxic waste to land in a reservoir. An exotic spider farmer named Joshua (Tom Noonan) has been making regular visits to the site, where he collects crickets for his spiders. Although the spiders have ingested the toxins, he is oblivious since the arachnids seem unaffected. Joshua shows Mike (Scott Terra), a local boy, his collection, which include Jumping spiders, Trapdoor spiders, Tarantulas, and orb-weavers, including a female orb-weaver named Consuela. After Mike leaves, Joshua is bitten by an escaped tarantula and accidentally knocks down the spider cages. He is killed by the spiders and, after devouring him, the spiders grow to even huger proportions.
On his way home, Mike is accosted by his mother, Sheriff Samantha 'Sam' Parker (Kari Wührer) and Deputy Pete pulling the toxic barrel out of the pond. Wade, the Mayor of Prosperity, is holding a town meeting in the mall about whether they should sell the mines and relocate. Chris McCormick (David Arquette), whose father owned the mines before he died ten years ago, shows up and stands against Wade's proposition. Chris also sparks a romance with Sam.
Meanwhile, Harlan Griffiths (Doug E. Doug), the local radio DJ and an eccentric extraterrestrial enthusiast, is broadcasting his theory that various missing pets around town have been abducted by extraterrestrials. Inevitably his theory is dismissed as the product of a deranged imagination. Mike sneaks out on foot to find Joshua but finds the spiders missing, the farm covered in webbing, and the dead body of Joshua. Although he sees an enormous spider shadow in the mines and tells Chris that the spiders have grown to enormous sizes, based on a giant spider leg he found at the mine entrance, Chris disbelieves his story. Meanwhile, the mines have reopened with the miners searching for a famous gold lode.
One miner is eaten by a gigantic spider, whose clan have made the mines their home. Seeing as the entire town is connected in some way to the mines, spiders show up in many different places. Deputy Pete Williams (Rick Overton) cat has a fight with one of the spiders in the air vents before being eaten, and some of the ostriches on Wade's farm are devoured by Trap Door Spiders, Ashley breaks up with her boyfriend Bret, and he and his motorcyclist friends are chased by jumping spiders, with him being the only survivor, accidentally cutting off the telephone line and being stuck in the mine. Chris finds out that his Aunt Gladys and her dog are abducted by a male orb weaver in their basement. Sam is convinced Chris and Mike are delusional. However, her skepticism fades and she realizes that Chris and Mike were right all along when she witnesses a giant male orb-weaver attempting to abduct Ashley (Scarlett Johansson), Sam's rebellious teenage daughter and Chris; Sam saves them both. Meanwhile Bret, still wandering the mines, gets a good peek at the giant Consuela during her feeding.
Sam contacts Pete and tells him to bring all guns in the police station's possession and they escape to Harlan's trailer, knowing he has a radio station that he operates from within his trailer. As Sam broadcasts the threat over the radio, a giant tarantula, the "tank" of the horde, assaults the trailer but they manage to escape. As the town is besieged by vicious spider hordes, many people are killed and eaten, Chris tries to convince Harlan that the spiders are "from Earth" but ends up convincing him that they are "Spiders from Mars" to make him happy, Sam tells everybody to evacuate to the mall. Chris, Sam, Mike, Ashley, Harlan, Wade and many other townspeople all escape and barricade themselves in the mall (but the cowardly Wade flees into the mines and locks the gate before the attack) and defend themselves from the spiders. Meanwhile, Harlan and Chris climb onto the roof and ascend the radio mast and try to get a signal to call the US army as they are being attacked by the spiders, but are believed to be pranksters. Harlan jumps from the roof, after the tarantula breaks open the gates and lets the spiders enter the mall, and lands in some bushes, where he meets up with Pete. The two run from spiders as Chris meets up with the remaining townsfolk and goes down to the basement. Meanwhile, Bret, still wandering the mines, encounters the cowardly Wade before his abduction.
While the townsfolk are in the basement, Bret arrives on a forklift that brings down the locked gate, and they all head to through the mines straight to the front entrance, discovering the methane-filled tunnels. After losing Norman and freeing Wade, Chris goes to look for his Aunt Gladys in the mines and finds her - and the gold his father was searching for, but is confronted by the gigantic Consuela. He uses perfume to distract the spider and then escapes using Bret's motorcycle. Chris then blows up the spiders and the mines utilizing Gladys's smoking addiction and the high concentrations of methane gas. The police finally arrive. They had not believed the reports of the spiders but believed Harlarn's theory that the assailants were extraterrestrial in nature, until Pete tells them that the assailants were "just spiders, that had ingested extremely high levels of toxic waste." He attempts to prove this by removing his hat, showing us that he is bald. He runs his hand back and forth over his head saying; "All new growth, just look at this, all new growth!"
In the final scene, Harlan is heard making a radio report about the spiders. He concludes that the town has decided to cover up the whole incident, but have let Harlan continue broadcasting the incident, knowing nobody will believe him. He also mentions Chris reopening the gold mines and putting everyone back to work, but tells us "that is another story altogether." As the camera zooms in close on his mouth, it is clear that he now has three gold teeth.
