Agro-Bots

Agro-Bots are huge, heavily-armoured machines once invented by the Martians of Mars to tend to the crop fields.

Description
Since these big machines are automated, they still mindlessly go through their now-useless tasks for a civilization that no longer exists. They usually ignore humans, but should an agro-bot detect one in its way or intruding into its fields, it will try to exterminate the "pest" that has "infected" the plants. Needless to say, fleeing is better than facing these huge machines in battle.

Usually found on the fields of Mars.