Thresher Maw
Biographical information
Homeworld:	Tuchanka
Status:	Active
Physical information
Height:	60 meters (only 30 meters is exposed at any time)
Skin color:	Brownish green
Lifespan:	200-300 years
Distinctions:	Four mandibles. Worm-like body with multiple legs and two retractable arms. Flexible back. Levo-amino chirality. One heart. Eight lungs.
Types:	Kalros
Political and military information
Nomenclature:	Daemonium de Arena Killer worms Threshers
Notable:	Kalros

"Standard protocol for fighting a thresher maw is to run the hell away...no, I'm serious. No fucker I know has been stupid enough to try and take one on foot. Only a krogan would be dumb enough to try and fight one."

— Zaeed Massani.

Thresher Maws (Latin: Daemonium de Arena, literally meaning "Demon of the Sand"), colloquially referred to as Threshers, are a sentient organic species of giant subterranean carnivorous worms native to their homeworld of Tuchanka and of the polychaeta classification. Similar to the bobbit worms of Earth, thresher maws are enormous carnivorous worms that roam the nuclear wastes of Tuchanka underground, bursting up from under the surface to feed on unsuspecting prey. Utilizing vibrations to hunt, thresher maws are extraordinarily violent, attacking anything and everything that disturbs them, even machines and vehicles: thresher stomach acid is extremely virulent and deadly, and they possess the ability to regurgitate and utilize the acid as a projectile, spitting it from their mouth to hurl at a victim: the acid is so potent that it can melt through most armor, and is lethal to most organics. Threshers also possess natural armor that covers much of their upper body, making them highly resistant to projectile-based weaponry and tough to kill: as such, thresher maws are used by the krogan during the Rite of Passage to test their participants, with the expectation that they must survive and fight off a thresher to pass the test: in exceptionally rare cases, participants may end up actually killing the thresher maw, but this is nor required or likely. The Tucker Doctrine, as established by the Systems Alliance following the Akuze Massacre, was that any foot units were to withdraw or avoid combat with a thresher unless in possession of vehicle-mounted ordnance, and even then this was to be used to fight off a thresher long enough to escape rather than kill it.

Following the krogan's introduction to the galactic community, thresher maws have spread to hundreds of worlds, with their method of reproduction allowing them to spread to virtually any world. Thresher maws reproduce via spores which can lie dormant for centuries, but once they hatch and begin to grow, they will birth a mature thresher maw in the span of just a few years. These spores can survive virtually any atmospheric conditions, including re-entry and the vacuum of space. Thresher maw populations are tightly controlled, limited to unpopulated worlds: planets that are heavily colonized have dedicated extermination practices for dealing with thresher maws before their populations can get out of control, largely by using neutron purges to cull them. To date the largest thresher maw population remains on Tuchanka, with the largest and oldest thresher maw in history being Kalros, known to the krogan as the "mother of all thresher maws" and the subject of one of the krogan's most ancient religions. Kalros' origins are hotly debated to this day, with some believing she may be part of an older species of extinct thresher maws due to her enormous size compared to standard thresher maws, and with no reported cases of any thresher maws living long enough to reach her size. Further proof is Kalros' age: being thousands of years old, her lifespan is in excess of that of a standard maw, who average a life of 200-300 years.