Question: How many steel roller coasters of the same type as The Swarm are currently operating worldwide?
Context: A mountain coaster or alpine coaster is a gravity-driven amusement ride with bobsled-like cars on tracks installed on a mountain.  It is similar to alpine slides where a low-wheeled sled is used to navigate the track, but instead of running over smooth concave tracks like the alpine slide, alpine coasters run on rails with up-stop wheels like roller coasters.  Thus, an alpine coaster isn't necessarily safer due to the jerky movements the cart makes as it navigates its way on a fixed track.  Alpine coasters are undoubtedly slower than an alpine slide since alpine coasters have speed regulated carts that prevent a rider from experiencing the track at full speed.  Tracks are usually tubular rails, like a steel roller coasters, while some have monorail-type tracks.  Unlike a traditional roller coaster, the rider has the capability to control the car's speed with its rider-controlled brake system.  Alpine coasters can also operate year-round, even through light rain and snow. Viper is a wooden roller coaster located at Six Flags Great America in Gurnee, Illinois, which opened in 1995.  Viper features a layout that is a mirror image of the Coney Island Cyclone and is the only roller coaster ever to be built directly by Six Flags.  Viper is also the only wooden roller coaster that has ever carried this name, (all the other Viper roller coasters, both operating and not, have been steel roller coasters).  It was built by Rygiel Construction. Roller coasters are amusement rides developed for amusement parks and modern theme parks.  During the 16th and 17th centuries, rides consisting of wooden sleds that took riders down large slides made from ice were popular in Russia.  The first roller coasters, where the train was attached to a wooden track, first appeared in France in the early 1800s.  Although wooden roller coasters are still being produced, steel roller coasters are more common and can be found on every continent except Antarctica. A steel roller coaster is a roller coaster that is defined by having a track made of steel.  Steel coasters have earned immense popularity in the past 50 years throughout the world.  Incorporating tubular steel track and polyurethane-coated wheels, the steel roller coasters can provide a taller, smoother, and faster ride with more inversions than a traditional wooden roller coaster. Backety-Back Scenic Railway was a wooden roller coaster located at Crystal Beach, Ontario.  The ride opened to the public in 1909 and operated until 1926.  The Backety-Back Scenic Railway was notable for a backward-traveling innovation which would be adopted many years later in more modern steel roller coasters.  It was also one of the earliest shuttle roller coasters to be built, as well as being the second roller coaster to be built in the Crystal Beach amusement park.  The coaster has been cited as a particularly beautiful example of roller coaster architecture. Roller coaster phobia is a colloquial and slang term describing an individual's fear of roller coasters.  While roller coasters are the most popular theme park attraction, certain people feel nauseated, afraid, dizzy, or unsafe when riding roller coasters.  In the majority of cases, this fear is related to acrophobia, claustrophobia, or a traumatic event.  Roller coaster phobia can be overcome relatively easily, the best cure being going on the tallest/fastest roller coaster before riding roller coasters of a lesser magnitude.  Roller coaster phobia has been linked to previously experiencing an accident, vertigo, and fear of heights.  In rare cases, riders may be afraid of roller coasters due to a painful ride, tight restraints, being thrown around in the restraints, and excessive g-forces on the body of the rider. 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. 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. Giovanola Freres SA was one of the prominent thrill ride manufacturers in the world.  It was well known for thrill rides and also built electrical power stations, water storage tanks, pipelines, highway bridges, and many other steel products.  The company started out as a small metal forging shop, founded by Joseph Giovanola in 1888.  It served as a subcontractor to Intamin supplying rides and roller coasters.  In 1998 Giovanola started marketing directly under the name Giovanola Amusement Rides Worldwide.  The company was based in Monthey, Switzerland.  During its last years in business, Giovanola fashioned steel behind the scenes for companies such as Intamin and Bolliger & Mabillard.  The company also built its own thrill rides and roller coasters from 1998 to 2001.  Examples of Giovanola roller coasters are Goliath at Six Flags Magic Mountain, Titan at Six Flags Over Texas and Anaconda at South Africa's Gold Reef City. The Dark Knight Coaster is the name of three enclosed steel roller coasters that are currently operating at Six Flags Great Adventure, Six Flags Great America and Six Flags México.  They opened in 2008 and 2009, timed closely to the theatrical release of "The Dark Knight".  The roller coasters are manufactured by Mack Rides.
Answer: eight