Question: How many steel roller coasters of the same type as The Swarm are currently operating worldwide?

Related documents: [0]  [DOC] The Swarm is a steel Wing Coaster at Thorpe Park, a theme park in the United Kingdom. "The Swarm" was the world's second Wing Coaster designed by Swiss roller coaster manufacturer Bolliger & Mabillard and the United Kingdom's first Wing Coaster. Construction commenced in May 2011, and the coaster opened on 15 March 2012. Starting in 2013, the last two rows of each train face backwards, while the first five rows face forward. This was removed in 2016, with all riders facing forward once again. [END] 
[1]  [DOC] A Wing Coaster is a type of steel roller coaster manufactured by Bolliger & Mabillard where pairs of riders sit on either side of a roller coaster track in which nothing is above or below the riders. Development of the Wing Coaster began between 2007 and 2008 leading to the opening of Raptor at Gardaland, the world's first Wing Coaster, on 1 April 2011. There are currently eight Wing Coasters operating worldwide. [END]  
Answer: eight
eight