"While some have theorized the tubes are used for spinning and cocooning the resin for their hive, that has generally been discounted as a fallacy. The current line of thinking is that the tubes are a type of breathing apparatus, filtering out airborne toxins and allowing the creatures to breathe underwater. However, as aliens have been observed surviving the vacuum of space, it is possible they do not need to breathe at all."
Alien: The Roleplaying Game

Dorsal spines on a NECA figurine.

Dorsal spines,[1] also referred to as protuberances or simply spines,[2] are tube-like structures that occur dorsally on most adult variations of the Xenomorph.


"Among other things, it introduces us to the PredAlien, which will become a feature of the AvP computer games, and shows us exactly what those tubes on the Aliens’ backs are for."
Beautiful Monsters regarding Aliens vs. Predator: Duel

Most adult forms of Xenomorph have been seen to exhibit a series of tube-like dorsal spines from their backs; notable exceptions are the Runner and Prowler, which lack dorsal spines altogether. In cases where they are present, there are typically four such spines arranged in pairs, with a larger pair close to the creature's head and a smaller pair beneath those. Their exact purpose is unknown, although studies conducted by Weyland-Yutani have concluded that they are part of the Xenomorph's respiratory system, acting as atmospheric filters and delivering the requisite elements to the Xenomorph's body, similar to spiracles found on Earth-based insects.[1] Several terrestrial aquatic creatures likewise use spiracles to absorb oxygen without inhaling water, explaining the Xenomorph's proven ability to remain submerged for extended periods.[1]


Queens and Praetorians[]


A Praetorian

Queens have a variation of the dorsal spines. Instead of actual tube-like structures, spines run down the back, numbering at six instead of four. Praetorians have a similar set-up along their spines and general appearance to a Queen, being genetically similar to a Queen Alien[2].

Predalien Bony Spines[]


A Predalien, lacking dorsal spines.

The Predaliens on LV-742 were shown to lack dorsal spines, prior to genetic evolution forced by the Queen. After the adaptation, however, they would gain dorsal spines in accordance to how tough their mesoskeletons were. The dorsal spines of the Predalien are notably similar to those of the Praetorian; it is unknown if this aesthetic similarity has anyting more behind it.

Runners and Prowlers[]


The Dragon, a runner Alien.

Runner and Prowler aliens completely lack spines, instead having a smooth back. For Runners, this is likely so that the creature, more tuned into its speed than its strength, is more aerodynamic, making it faster. However, this could be a side effect of a non-humanoid host. Prowlers, a more recent Xenomorph variant, is similar to the Runner and also lacks dorsal spines. However, instead of speed, it hides among Runner packs, blending in among them, in order to ambush prey.

Runners, when they evolve into Sentries, do eventually evolve Dorsal tubes. They maintain them even in their final evolutionary forms as Crushers.

Carrier Launching Spines[]

Carrier model

An upgraded carrier.

Carrier Xenomorphs have specialized back spines called "Launching spines", which have evolved to carry around the otherwise vulnerable Facehugger. Their spines shed nutritious material that Facehuggers consume while aboard them called "Exadrenaline". When evolved by a Queen, these spines can carry up to 12 facehuggers and nourishes them so that they may travel farther than normal to find a suitable host.


  • The Xenomorph's creator, H. R. Giger, originally included the spines in the creature's design to balance out its elongated head.[3]
  • Alien writer Dan O'Bannon originally wanted the spines to extend from the Alien's chest, but director Ridley Scott ultimately chose to have them on the creature's back.[3]
  • In Alien: Isolation, the Alien's dorsal spines can be seen vibrating from time to time when it stands still and is searching for the player. This may indicate the spines are a sensory organ of some sort.[4]
  • Xenomorphs have been seen swimming in sand and water with their dorsal spines protruding from the surface, not unlike a shark. It is unclear why they do this.
  • In the video game Aliens versus Predator: Extinction, the number of dorsal spines is directly related to the strength of an individual Xenomorph.



  1. 1.0 1.1 1.2 Weyland-Yutani Archives (2008), 20th Century Fox [Blu-ray]
  2. 2.0 2.1 Aliens versus Predator: Extinction, EA Games, 2003.
  3. 3.0 3.1 "Monster Legacy - Star Beast — Alien". Retrieved on 2017-02-22.
  4. Alien: Isolation, Microsoft Windows, PlayStation 3, PlayStation 4, Xbox 360, Xbox One version, Creative Assembly, 2014.