Thresher maws were somehow distributed to other planets when the krogan race was given interstellar spaceflight technology to fight in the Rachni War. They have since become dangerous pests on many worlds.
Thresher maws can grow to hundreds of meters in length, and their thick carapaces are difficult to damage. They are fast burrowers, and they can spit acidic slime.
Thresher maws are sensitive to vibrations in the ground, which they use to detect prey and rivals. The krogan use devices called "maw hammers" to attract them for rites of passage.