Skelerakks are an undead form of Rakk, presumably reanimated or otherwise affected by Dr. Ned's experiments. They are still able to fly, even though they lack any wing membranes to fly with.
Skelerakk have much higher health than normal Rakk, and are found on the coastline of Jakobs Cove and Generally Hospital. They generally do not attack unless they are approached or are shot at.
Shotguns and high rate-of-fire weapons are effective at countering the threat posed by a skelerakk. Explosive element is recommended.