Michael Nies wrote an answer about La Sportiva Tarantulace Climbing Shoe on June 23, 2014
Since climbing shoes need to have a snug (NOT TIGHT!!!!) fit, many climbers recommend getting climbing shoes a US size smaller than your street shoe size. By that logic, if you wear a size 44 in street shoes, you should aim for a size 42-42.5 for your climbing shoes. La Sportiva fit, though, is a strange animal, and tends to run much smaller than street shoe size. I wear a US 14 (Euro 48) in street shoes, but a Mythos 44.5, a Testarossa 45, and a TC Pro 45.5. The only way I know this is because I tried on lots of shoes until I found what fit.
Unfortunately, getting well fitting climbing shoes isn't quite that easy, as several people have pointed out. Different shoes fit differently, and the only way to know is to try them on. These are definitely good starter shoes, and you can send them back to Backcountry if they don't fit. For your first pair you want something that is snug, but not painful. These will stretch (as will most climbing shoes), so starting with a pair that is a bit snugger than you think is comfortable is advisable. Good luck, and welcome to the rabbit hole that is climbing shoe fit!