Jairus Dennis, a packer for the ritzy online retailer Gilt Groupe, works on a kind of warehouse dream team. Every few seconds, colleagues fetch him heavy shelves stacked with skinny jeans and red dresses. No one ever complains or slows down.

Dennis's colleagues are orange and just 18 inches tall: they are robots, and they do much of the work in Gilt's sprawling logistics center near Louisville, Kentucky. Sixty of the automated dollies crisscross the floor carrying shelves to humans, who pick, pack, and ship items without ever taking more than a couple of steps.

Dennis, a 21-year-old who has worked in the warehouse for a year and a half, likes the robotic help. "I prefer it. You don't have to walk around eight hours a day," he says.

The presence of the robots reflects a major shift for warehouses, where conveyer belts, forklifts, and a lot of manual labor have been the norm. Until recently, robots were too awkward and expensive to make much of a difference. But that is changing as Web retailers look for an edge in a business with low margins and sharp competition.