Thresher Maw

Thresher Maws are subterranean carnivores that spend their entire lives eating or searching for something to eat. They are enormous, violent creatures that burst up from the ground without warning when disturbed.

They reproduce via spores that lie dormant for millennia, yet are robust enough to survive prolonged periods in deep space and atmospheric re-entry. As a result, thresher maw spores appear on many worlds, spread by previous generations of space travelers.

Description
Thresher maws are solitary creatures; two or three at most can be found on a single planet. They live alone in nests spanning large areas underground. They can grow to be in excess of 30 metres tall above the ground, with a body nearly twice that size beneath the surface. The body of an adult thresher maw never entirely leaves the ground; only the head and tentacles erupt from the earth to attack.

Aggressive and highly territorial, thresher maws feed by absorbing huge amounts of solar radiation and survive best on planets, asteroids or moons with little or no atmosphere. They also consume minerals and ores from the ground itself and use an odd form of photosynthesis to combine solar radiation and minerals into energy they can use to fuel their significant mass.

Due to their size, and their burrowing style of movement, thresher maws are immobile above ground, but can move incredibly quickly below. They can take a lot of damage and can be very hard to kill. Their attacks consist of spitting powerful viscous acid that splashes on contact, burrowing up from beneath their prey, and smashing with their claws in close range while emitting infrasound. Due to the nature of their attacks, they completely ignore shields.

History
The Alliance first encountered threshers on the colony of Akuze in 2177. After contact was lost with the pioneer team, marine units were deployed to investigate. The shore parties were set upon by hungry threshers, and nearly the entire assault force was killed. Since then, thresher maws have been discovered throughout the galaxy, surviving even severely hazardous environments. Their physical and biological origins are unknown, although it is widely assumed they were "spread by a previous generation of space travelers", possibly before even the asari.

If Commander Shepard has the Sole Survivor background, Shepard alone survived the thresher attack on Akuze. However, Shepard may later encounter a second survivor in the mission UNC: Dead Scientists, Corporal Toombs, who claims that a black-ops group called Cerberus caused the massacre at Akuze deliberately. He says Cerberus scientists wanted to study the thresher maws, so they let them kill not only the colonists, but the marine rescue team as well, to watch and study. Cerberus was delighted that Toombs survived and held him captive for years, using him for experiments. It is likely Toombs' story is true, as Cerberus used a similar technique six years later, luring Admiral Kahoku's marine team to their deaths in a thresher nest on Edolus.

Habitation
The thresher maw usually lives in large flat open spaces on uninhabited planets. Thresher maws do not inhabit rolling hills, mountains, or valleys.

Specifically, thresher maw nests are uniquely identifiable by a distinct profile of landscape, which consists of a few hills and pits no higher or deeper than 2 meters on an otherwise perfectly flat circular area of land about 50-75 meters in diameter. Although barely discernible from radar, it becomes more apparent once it is seen from above. From below, it may appear as a jagged circular terrace. Thresher maws will not rise from the ground upon the hills or pits in their nest. They will retreat below ground if you leave their circular area for longer than about 5 seconds.

Threshers commonly have some sort of "lure" in their nest, such as a crashed probe to draw unwary scavengers, but there are some "stray" nests, identifiable only by their landscape profiles.

(This landscape profile may be a design decision to reduce development time to allow them to be "painted" onto maps in a single stroke, or more likely, it is to support their "rising from the ground" state of animation being correctly aligned with the surface of the terrain, and to ensure they have a radius in which they can attack without obstacle.)

In the Mako
When driving through thresher maw nests, be on your guard. They will abruptly rise from the ground after a short delay once you intrude on their nest. Once you hear a thresher rising up, look for it and put some distance between yourself and it quickly.

You should only try to attack one from a distance, because their melee attacks are devastating and rarely leave survivors. They have a sizable range beyond their appearance due to powerful infrasound. The ranged acid spit attack is fairly easy to dodge with propulsion jets as it is slow, as well as causing less damage.

The quickest way to eliminate a thresher maw is circle-strafing and shooting the Mako's cannon at it. If you must stop to snipe, time your stop immediately after a spit has passed you by, or otherwise when the acid has a trajectory that won't hit you or your team. It a good idea to use the Mako's cannon as much as possible in combination with the coaxial machine gun, in order to produce the most damage. However the Mako can be substantially damaged or destroyed in a single direct hit from an acid spit. If you are on foot and your Mako is destroyed by acid spit, do not get back into it -- go to the map screen and return to the Normandy instead.

An alternative strategy involves timed jumps and holding still. It appears that Thresher Maws only retreat underground and resurface if you move too far from them in the Mako or if you move a significant amount in any direction (closer or further away). Immediately after the Thresher surfaces (ideally for the first time), stop moving. Each time it spits acid at you, simply use the Mako's boosters to jump over the attack. If timed correctly, you should be able to avoid the attack ad infinitum. You may incur a very small amount of splash damage using this technique but the amount is negligible at best. If you continually hop over the acid while shooting (movement caused by aiming will not affect this method) you should be able to defeat any Thresher Maw with ease. It must be noted however that this technique relies heavily on positioning--if you are too close, you may not have enough time to react.

On Foot
If you kill a thresher while in the Mako, you receive significantly less experience. If you want to get the 'on foot' experience reward but still use the Mako's firepower, get the thresher maw down to as little health as possible using the Mako, then get out and finish it off on foot.

As thresher maws are unarmoured without special resistances, even your pistol can kill one. Use damage boosting skills as much as possible. Using Warp can reduce the thresher maw's defenses considerably. Even if you can't see the thresher's life meter or bullet impact effects on it, rest assured you're doing damage as long as you're aiming at it. Be certain to stay out of its melee range, as it is closer than it physically appears to be. Don't attempt to determine its melee range, just stay back. Keep enough distance between you to enable you to determine the path the acid spit is taking.

While circle strafing, your party members prefer to stop longer than you and don't even try to dodge the incoming attacks, so try to shoot while continuing moving in a linear fashion. They may still run into acid spit aimed for you, and you may take splash effect damage off of them, so find a semi-circular pattern that avoids this.

Whether combating a thresher maw in vehicular or infantry combat, you should be aware of your odds of survival. When on foot, the acid's splash effect may kill you, even if it doesn't hit you directly. High level Soldier health regeneration, and/or Medical Interface that provides toxic resistance can mitigate this considerably. Surviving a direct hit from an acid splash requires a very high amount of health, as it completely ignores shielding.

If you are fortunate enough to be a Bastion, try using Stasis to buy yourself some time.

Locations

 * Antibaar
 * Chohe
 * Edolus
 * Nepheron
 * Nonuel
 * Presrop
 * Trebin
 * Xawin
 * Tuchanka

Oddities
You get experience twice when killing a thresher maw - once when its severely injured and once again when it dies. It is unknown whether this is a bug or intended behaviour. In consequence, when playing on hardcore difficulty, do not mistake the first experience reward for an indication that the fight is over, or you might be in for a nasty surprise.

Unlike other enemies in the game, such as Geth Armatures, thresher maws do not have to be even close to looking in your direction to perform any of their attacks, so do not attempt to drive into or melee attack one.

Trivia
Thresher maws appear to be inspired by the giant sandworms of Frank Herbert's Dune. Their reproductive method is very similar to the Sarlacc of Star Wars.