This is not about the cute Holywood variety of gremlins by Joe Dante. I am interested in the one that Wikipedia describes thus:
A gremlin is a folkloric mischievous creature that causes malfunctions in aircraft or other machinery. Depictions of these creatures vary. Often they are described or depicted as animals with spiky backs, large strange eyes, and small clawed frames that feature sharp teeth.
The real requirement here is an animal that, for whatever reasons, attacks airliners in mid-flight. The creature is likely able to match aircraft in flight ceiling and speed.
Evolutionary pressures leading to this and the creature's motivation (food, territory defense maybe?) are not required, but would be nice to have.