Lipole

Lipoles are flying, bat-like organisms indigenous to Jupiter's moon, Io. They consume metal the find and appear to continue growing over time, and the oldest individuals can become enormous; however most are far smaller, indicating that most will likely die off before ever growing to a full size. This is likely due to their surprisingly suicidal nature, somehow transforming into a missile shape and flinging themselves at predators.

Small lipoles, despite consuming metal, can be frightened off with a handgun, though this seems to activate their defensive nature against predators, causing them to transform into a suicide missile and launch themselves at a foe or their transportation.

Giant lipoles seem to glow with radioactivity and drool acid, although why this is is unknown. Despite appearing to be mechanical in nature, they are referred to as "bags of protoplasm".