Lurker

Lurkers (Russian: singular Кикимора) are a pack-based species of burrowing mutants in the Metro universe.

Overview
Lurkers are comparably small creatures that are on the lower ends of post-appocalyptic food chain. They are very fast, with a tendency to jump up from holes in the ground and launch themselves at threats or food. They often show up in packs of one to three at a time, even if more are in the area. Lurkers are mostly scavengers that press in upon carcasses, and rarely hunt live prey. They have almost pink skin and no body hair whatsoever. They also possess a second pair of eyes, which are very small and probably useless as they appear to be milky white (a sign of blindness).

Lurkers congregate in recently abandoned metro stations, feeding on the corpses of humans and mutants alike. They have warrens, burrows that allow the lurkers to transit between holes as a means of flanking prey. The holes that they use are often (if not always) above lower rooms of the stations, indicating that their burrowing abilities are not very good and that they prefer to use large, empty spaces to save them the trouble of digging a new warren.

Lurkers tend to only attack lone humans as opposed to large groups, another behavioral trait of scavengers, such as when Artyom is making his way through Hole Station and carrying Sasha. Bourbon warns Artyom of this early in the game when a lone lurker is seen fleeing before them.

The lurkers of Metro: Last Light look completely different than their counterparts in Metro 2033. They have light brownish tan skin, a short neck with a pronounced droop, and a head that resembles a cross between a reptile's and an insect's with very small, beady eyes. This dramatic change may simply be attributed to artistic license, but it could imply that the name lurker is just a catch-all term for a number of mutant species, many of which may be related to watchers.

Metro Exodus features a redesigned lurker. This variant has the appearance of a hunchbacked, very large, simian-esque rat. The lurker's body is covered in pink skin and mangy black fur that seems to be balding heavily around the head and chest areas. It has large back paws twice the size of its front paws, and possesses opposable thumbs. The large back paws are possibly an adaptation that helps in the digging of tunnels. These variants also appear to be much more aggressive and are prone to attack, even when unprovoked.

Tactics
Dealing with lurkers depends on how they are approached. While individual lurkers can cause severe damage, they frequently attack in groups at a time. After striking or missing contact, they will retreat into their holes. Caution is advised, however, as they can come out of the holes behind Artyom at any time.

Moving into lurker territory with guns blazing is not recommended. Instead, trying to find a spot where there are no holes behind, like a solid corner or structure with one entrance, will guarantee a better chance of survival. If Artyom moves into the middle of their territory, he will provoke them, if this happens, retreat to a safe spot. Doing this will force them to run squarely into the barrel of a revolver (or any other weapon), which can dispatch any lurker with one shot to the head (an easy shot to make when they are running straight at Artyom). Shotguns are also a good choice, but only at Hardcore or Ranger difficulties where its stopping power is large enough so that Artyom can take them out at longer distances. Like most melee enemies, however, they tend to jump when they are close. That means Artyom may pull the trigger just as they are flying over his line of fire.

It should be noted that lurkers are the only mutants that are actually more dangerous in Ranger pack difficulties. Their normally modest damage is made much higher, and their mobility is their defense, so increased damage of Artyom's weaponry will not help as much. Because they attack fast and in groups, Artyom can be shredded in a matter of seconds.

Similar tactics as used against librarians can be used against lurkers, as they usually do not come out of their holes if the player character looks at them, and tend to attack from the opposite direction. They often retreat if the player character spots them while trying to sneak up from behind. This could be very useful when playing in ranger difficulties as they are much more powerful. It's advised to not rely completely on this, however, as they might still come out and attack.

When dealing with lurkers in the area requiring a gas mask in "Defense", it's best to provoke them and then retreat to an area with no gas (like at the top of the stairs). Otherwise, they might seriously damage the player character's mask.

Lurkers will rarely appear out from a burrow the player character is staring at, instead, milling about beneath, waiting for them to look away, given away by the sounds of their movement and growls. A stick of dynamite down the warren (provided it doesn't fall too far down) will kill any lurkers nearby.

As a final note, there are no places in the game where lurkers spawn indefinitely. Even in the first area of "Child", they will eventually stop spawning (Artyom will need to kill somewhere in between 20 and 40 of them, however).

Trivia

 * Kikimora, (sometimes anglicized as "Kikimore") the name used in the Russian translation, comes from Slavic mythology. The Kikimora is described as a small humpbacked woman, with a thin body and small bird-like head. Creatures with the same name also appear in another game series by a Slavic studio, CD Projekt, namely in the Witcher series (they appear in both The Witcher and the The Witcher 3: Wild Hunt, as well as in the Wiedźmin book series by Andrzej Sapkowski, on which the games are based upon/are continuation of).
 * If Artyom falls down a hole belonging to a lurker, the sound of gnawing on his body can be heard, shortly before he dies. Likewise, in 2033 Redux, this results in a short cutscene of Artyom falling down the hole, followed by a Lurker jumping in and pouncing on him.
 * According to the game developers, these monsters are truly navigating their way between their holes in the game, not just being placed in a random hole near Artyom.
 * Lurkers are the only mutants known to have been domesticated in any numbers. A performer at Theatre Station uses one in his show (though it's rather poorly trained or the creature itself is not suited for training for show), and Kuzmich owns a much smaller and more tamed one that he allows to perch on his shoulder; thus they are one of the few mutants that do display a considerable degree of intelligence.
 * The Metro 2033 model is used for baby watchmen in "Dead City" in Metro 2033 Redux. All instances of actual Lurkers, on the other hand, are replaced by the Last Light model.
 * While the lurker is usually identified along with the watchmen, the game series shows the lurkers are indeed a separate species as their dwellings/nest and behavior towards the watchmen are noticeably differentiated or hostile.
 * It is unknown what the Lurker might have mutated from, but considering their average quadrupedal form along with a noticeably elongated tail, it's possible that the animal might be the heavily radiated and mutated result of pre-war cats. This would also explain their tendency to attach to humans and capacity for being domesticated. Although other explanations, such as smaller dog breeds or even large rats, are highly possible. However, the re-design/appearance of the lurker for Metro Exodus openly confirms that they are likely descendant/evolved (albeit heavily altered/mutated) from large rodents. Most likely the semi-feral rodent population of Moscow and perhaps Siberia.
 * Lurkers were suspected to be juvenile/sub-adult stage of watchers. There are notable visual similarities between the two, both physically and behaviorally. This is evident in "Defense" when a lurker can be seen performing a rare start-combat animation, the watcher's trademark pose. Furthermore, in Metro 2033, both lurkers and watchers had two sets of eyes, and in Last Light, both now only have one set of eyes. Both hunt in packs, share the same general body composition, and very similar movement and attack animations. However, there is no concrete evidence to legitimize this claim. The creatures potentially exhibit what is deemed similar behavior as a result of sharing, potentially, the same ancestor, or a result of convergent evolution to adapt to the same ecosystem. The games also seem to differentiate the two creatures; this is more evident in Metro: Last Light. This is further re-enforced in Metro Exodus, as that game features a considerable redesign of both species, with the lurker now resembling a rat much more closely.
 * Lurkers are, very likely, on the lower ends of the post-apocalyptic world's food-chain. Despite their enlarged size and intelligence, they are likely hunted by every predator on the surface such as demons, watchmen, elder/adult shrimp, and even nosalis. Seeing as their scavenging (and likely hunting smaller creatures) and elusive/more prone to run rather than attack/behavior, along with the fact that lurkers are more of an underground dwelling species, it's likely lurkers come to surface only when they have to.
 * While exploring the railway terminal in the Volga level of Metro Exodus, Artyom will encounter several dead lurkers and fanatics atop one of the concrete fuel storage tanks. Upon closer inspection the lurker corpses are those of Last Light's lurkers, rather than Exodus' lurkers. This might suggests a differentiation on lurkers (as different breeds/variants/subspecies). Alternatively, it could be an oversight, or even an Easter Egg.
 * The Last Light lurkers are encountered a second time while infiltrating the Munai-Bailer oil rig in the Capsian level, where they are found alongside dead spiderbugs.

Gallery
Кикимора