Oxy-Leeches

The Oxy-Leech of Mars feeds on the material Oxium. The leech itself -- despite being probably one of the most disgusting sights on the planet -- isn't a threat in combat. It does next to no damage and is easily killed. Its true danger lies in that it snatches and devours the needed Oxium at an alarming rate, leaving the adventurer with bare hands, since Oxium is needed to breathe without too much trouble in the atmosphere of Mars.

Therefore, oxy-leeches should be killed from a distance with maximum prejudice.

Trivia

 * This creature fulfills the same purpose on Mars, as gremlins do in Britannia: eating away the rations (here oxium) at an alarming rate, while doing little physical damage.