The scariest thing about freshman director Carter Smith's new horror movie "The Ruins" is the closing credits that list comedian Ben Stiller as one of the executive producers. What was Stiller thinking when he sank his bucks into this chiller about cursed carnivorous undergrowth that creeps up on its victims and devours them. Oscar-nominated scenarist Scott B. Smith of "A Simple Plan," adapting his own bestselling novel, sticks steadfastly to the standard clichés and conventions of all twentysomething scary sagas where reckless youth do everything but tote signs begging the forces of evil to eat them. Were cretinous characters not enough to contend with in this nihilistic nonsense, we're treated to yet another film where American tourists find themselves in jeopardy simply because they are Americans. Furthermore, unlike really good horror movies that explain why the monsters have a need to feed, "The Ruins" provides no explanation for the supernatural shenanigans of its villainous vines. <br /><br />The set-up for "The Ruins" resembles the 2006 horror movie "Turistas" where slimy South Americans trapped brainless American backpackers and harvested them for their internal organs. Indeed, "Turistas" generated some legitimate thrills and chills. "The Ruins" spawns nothing in the way of either thrills or chills. A malicious mastiff that suddenly lurches on-camera to snarl at our heroes is as close as it gets to a thrill. <br /><br />The rest of "The Ruins" borrows from another movie: "The Descent," a superb, 2006 chiller about a bunch of babes plunged into a nightmare experience when they get lost in warren of caves inhabited by albino mutants with a blood lust for murder. A couple of other movies that served either intentionally or unintentionally come to mind, too. They are the straightforward 1968 Hammer horror classic "The Lost Continent" about murderous vegetation that menaces innocent bystanders in a sea of derelict ships and the Roger Corman cult class "The Little Shop of Horrors" (1961)about a New York florist that grows a man-eating plant in his shop.. <br /><br />"The Ruins" unfolds in the scenic, sunny Mexico where four frolicking American college kids, Eric (Shawn Ashmore of the "X-Men" movies), Stacy (Laura Ramsey of "The Covenant"), Jeff (Jonathan Tucker of "Sleepers") and Amy (Jena Malone of "Pride & Prejudice"), are wrapping up their tequila-soaked spring break. Stacy loses a prized earring in a motel swimming pool, but a helpful Teutonic, twentysomething tourist, Mathias (Joe Anderson of "Copying Beethoven") recovers it, and the group embraces him as newest best friend. These people live to party, and they have already made friends with a trio of Greek tourists. Mathias tells them about his wayward brother who has accompanied a cute female archaeologist to a remote Mayan pyramid that isn't listed in any guidebooks. He offers to take them with him and they accept. <br /><br />First rule of horror movies: if nobody knows about the place where you're going, you'd be well advised to avoid it. Since they have only one day left, and they haven't done anything adventurous, our two couples along with their Spanish-speaking Greek friend, Dimtri (newcomer Dimitri Baveas), decide to follow Mathias and check the pyramid out. They catch a bus into the interior of Mexico and look for a taxi to take them on the next leg of their journey. A cabbie glances at their map and warns them to stay away. Second rule of horror movies: when the natives warn you to steer clear, you steer clear. A crisp twenty dollar bill helps him change his mind, and he hauls them off to their destination and then he skedaddles in a heartbeat. <br /><br />No sooner have our heroes found the mysterious Mayan pyramid covered with undergrowth that looks suspiciously like a variation of Mississippi kudzu in the jungle than superstitious natives appear. They know that the pyramid is haunted, and they kill Dimtri without a qualm when he tries to dispel their fears. The remaining protagonists scramble to safety atop the pyramid while the paranoid natives surround them to prevent them from escaping. Eventually, the vines slink out to greet our heroes and eat them. At this point, "The Ruins" turns into "Bug," the recent and ridiculous Ashley Judd schizoid movie about insects that get under your skin. Before long our heroes are carving each other up in a futile effort to extract the vines from under their skin. One particularly gruesome scene shows the Americans lopping off the German guy's legs to save his life. By comparison, it makes the tortures of the Spanish Inquisition look tame. <br /><br />"The Ruins" ranks as just another vine mess with nothing to redeem it.