From Destinypedia, the Destiny wiki
Shanks are small floating drones employed by the Fallen as scouts, fire support, or to serve as a distraction. They are propelled by a pair of vertical jet engines which allow them to both fly and hover in the air. Standard shanks are only equipped with a weak, rapid-fire, Arc-based weapon, and are rather fragile, in that they can be destroyed in only a few shots. Although, during Nightfall Strikes and certain Public Events, Shanks can have a Solar shield, making them more difficult to dispatch. Individually, they are little more than a nuisance, but they are often found in swarms, or as part of a larger group of Fallen, which makes them considerably more dangerous. They can also be spawned during battles with Fallen Walkers.
In addition to the standard Shanks, some Fallen Houses also employ different varieties which possess different characteristics. For example, the House of Wolves utilize Repeater Shanks, which act as fire support, Exploder Shanks, which act as a kamikaze unit, and Tracer Shanks, which act as snipers.
List of appearances