Swarms

Certain insects like locusts create natural swarms, but occasionally people have encountered swarms of creatures too numerous, too large, and too violent to be explained by nature. These swarms are formed of creatures bound together by fell magic, and they are incredibly difficult to fend off through normal means. Combat is ineffective, and what's worse, the swarms surround and attack any and all creatures they come across, burrowing into clothes, hair, sometimes even the skin of their victims, occasionally creating aggravated wounds or causing their victims to become ill from the sensation. They can be fended off with fire, which can spread rapidly through the tightly packed bodies of the swarming creatures, or endured if shelter from them can be found. Do not try to outrun them, many swarms (especially aerial swarms) can descend on their prey with frightening speed.