Gecko (Fallout: New Vegas)

The gecko is most likely the first hostile creature to be encountered by the player in the Mojave Wasteland. Sunny Smiles describes them as "little monsters" who are "quick with a nasty bite."

Biology
Geckos can be found living across the entire Mojave Wasteland, although different species of gecko tend to live in different areas. There are three types of gecko in the Mojave: the "normal" gecko, the golden gecko, and the fire gecko. Another variety, the green gecko, is found in Zion Canyon in the Fallout: New Vegas add-on, Honest Hearts. Geckos in general are reptilian in appearance and tend to have a pair of fins behind its head. Their eyes are an orange tint, and their body colors differ greatly based on the gecko type. Geckos also all have five fingers and five toes.

Gameplay attributes
Geckos are generally found in small packs. They will charge at you quickly with their mouths open and attack rapidly with bites and swipes from their clawed hands. The most common reason for a player's death is a result of them letting a gecko get too close, which ends in a ravaging assault in which the player can't target the gecko. Therefore, the gecko kills the player because he/she can't hit the gecko with a ranged weapon. A melee weapon will work, but needs the gecko to be in close. When the player blocks the gecko's first strike, the gecko retaliates with surprising speed. All in all the gecko can be dangerous up close, but at a distance is easy to kill.

The standard tactic of a gecko pack is for the bulk of the group to attack head-on with the remainder of the group attempting to flank the player. Combined with the gecko's savage melee attack, This can prove a smart strategy. Unfortunately it is often short lived if the player is a higher level.

With a high survival skill, tanned gecko hides can be used to back leather armor or metal armor, strengthening its defensive capabilities and adding resistances to poison and other hazards.(Gecko-backed metal armor,Gecko-backed leather armor) This also works on the reinforced variants.

Geckos, green geckos, and golden geckos are affected by the Animal Friend perk. Fire geckos are not.

Gecko
Generally found in packs, geckos charge with mouths open and attack with bites and swipes from their clawed hands. Geckos can be found mostly around the areas surrounding Goodsprings and along I-15, towards Primm and the Mojave Outpost. This is the least dangerous species of gecko and can be easily killed even by lower level players.

Gecko hunter
These geckos do the hunting for the pack with deadly efficiency. They are very fast and use their numbers to rush and overwhelm the player. With greater strength and health, gecko hunters are more troublesome than normal geckos, particularly for lower level players.

Young gecko
Your standard geckos who have yet to mature fully. Despite being smaller and less damaging than your regular gecko, they can still be a problem to low level players when there are many of them.

Young gecko hunter
Geckos who yet to mature fully, yet are matured enough to go out on the hunt and learn from their parents and other pack members. They generally don't attack the Courier without reason.

Golden gecko
A type of gecko with brilliant golden scales. These are found around irradiated areas like Clark Field, Vault 34, and Cottonwood Crater. Golden geckos have been affected by high levels of radiation and as such, when they attack the player, they will become irradiated each time they take a bite.

Young golden gecko
Golden geckos who have yet to mature. They will seldom be alone and typically travel in packs with other, adult lizards.

Golden gecko hunter
These geckos go out on the hunt and bring back the food for the gecko pack. They can usually be found in packs of four to six, searching for an unaware creature to make lunch out of.

Fire gecko
Fire Geckos are the strongest form of gecko found in the Mojave (excluding Honest Hearts green gecko as seen below). Long after the regular and golden geckos have ceased to pose a serious threat, the fire gecko can remain dangerous even to high-level characters. Fire geckos are easily recognized by their spike-covered bodies, mottled purple-and-red hides (prized by trappers for making armor), and the quality that gave them their name: they can breathe fire.

It is hinted that their fire-breathing capability is derived from constant exposure to sulfur, due to the fact that there are many fire geckos in the sulfur caves of Vault 19.

Young fire gecko
These younger fire geckos still sport their parents' blue-violet hue, but are much weaker with shorter spikes running the length of their body. Don't underestimate these beasts because they're young; a pack of these can still be lethal.

Legendary fire gecko
The "king" of the fire geckos. It's roughly twice the size, twice as hardy, and twice as hard to kill. The legendary fire gecko is one of the four legendary creatures in the game. This "king" of fire geckos can be found in Fire Root cavern.

It is the second weakest legendary creature, sporting only 135 more HP and 15 more attack damage than the legendary night stalker.

It's powerful and fast attacks make the legendary fire gecko a potentially dangerous opponent in close combat.

Green gecko (Honest Hearts)
Green geckos are native to and only found in the Zion Canyon, and are even stronger than fire geckos. They can spit several slow-moving and far-reaching globs of poisonous saliva similar to centaurs.

Young green gecko (Honest Hearts)
A young, immature green gecko that is a lesser threat than adult ones, but still can spit poisonous saliva projectiles.

Giant green gecko (Honest Hearts)
Another type of giant creature living in Zion National Park, these geckos are larger than a human and have almost the same destructive power as the Legendary fire gecko.

Appearances
Geckos appear in Fallout: New Vegas.

Behind the scenes

 * Another type of fire gecko exists, but was cut from the final product. Its name is Gojira. Simply called "gecko" when spawned, Gojira is its editor ID. It's identical to the fire gecko, but about triple the size and has a whopping 8,000 hit points. Gojira is the original Japanese name of Godzilla.
 * Before the release of Honest Hearts, the green geckos were mistakenly referred to as "Greek geckos" in press material. This was corrected before the release.

Bugs

 * Geckos may not always be hostile to the Courier, even if the player doesn't possess the Animal Friend perk. However, getting too close or trying to speak to one may turn it hostile.
 * In the Mojave Desert, several young gecko hunters may be found superimposed upon one another, but not moving from the spot except to flail their arms and roar loudly. They cannot be damaged with guns, and when attacked and killed with a melee weapon, the game freezes and must be reset.