Oxy-Leeches

The Oxi-Leech of Mars feeds on the radioactive material Oxium. The leech itself -despite being proably 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. It's 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 kill them from a distance with maximum prejudice.