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Dorsal tubes

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Dorsal tubes on a NECA figurine.

The Dorsal tubes, also called protuberances and spines[1], are structures that occur dorsally on most variations of the Xenomorph and are arguably the most mysterious piece of external anatomy on the creature.



Unlike the inner jaw and acid blood of the Xenomorph, the dorsal tubes do not seem to have any purpose. They are never referenced in the films or games and even the expanded universe doesn't make much mention of them. As a result, their purpose -- if there is one -- is largely unknown.

Possible ExplanationsEdit

Swimming AssistanceEdit


Xenomorphs approaching Two-Stripes.

Xenomorphs have been known to use their dorsal tubes in a manner similar to that of sharks. Like a shark, its tubes will break the surface of either sand[2] or water, while the rest of its body remains hidden. Despite popular belief and media depictions, sharks only rarely do this, typically because they are lured to the surface or are simply swimming in shallow water.[3] The tubes would be counterproductive to a Xenomorphs hunting for obvious reasons if used in such a way, so they may just be used for underwater steering, again similar to the shark.[4] If this is true, their lack of use on land is because they have no use on land.

Hunting ToolEdit


Xenomorphs "swimming" through soil.

Some media have portrayed Xenomorphs as "swimming" through soil, with their dorsal tubes above ground. For obvious reasons, this doesn't appear to be an attempt at stealth. Rather, it may be a hunting technique, as this would inspire fear and either a flight or fight response. Similar to wolves, Xenomorphs may use their dorsal tubes to panic and scatter prey, so that the slower, weaker individual will be revealed. They then go after these prey items, harvesting or killing them.[5].

However, the Xenomorph doesn't appear to be terribly discriminate in what it attacks. More dangerous enemies are handled with more care, but attacked all the same, so this may not be the case.

Vestigial AnatomyEdit

The dorsal tubes may have no inherent use and, assuming the Xenomorph is a natural creature, just may be a vestigial piece of anatomy, similar to how whales retain their pelvic bones despite lacking hind limbs and Humans retain their appendixes and coccyx, despite no longer being able to safely consume raw meat and lacking tails.

Temperature ControlEdit

The Xenomorph aversion to fire[6] and possibly any kind of extreme heat is well known, therefore the dorsal tubes could act as a cooling system or all around temperature regulator in more humid environments, still allowing the alien to function in an otherwise uncomfortable climate. The dorsal fin[7] of a sailfish and ears of a fennec fox[8] serve the same purpose.

Non-Universe ExplanationsEdit


One image from the Necronomicon, featuring a Xenomorph-like creature with it's dorsal tubes.

It is possible the dorsal tubes were added without much thought to their actual purpose concerning the creature. Instead, their protruding appearance may simply be fitting the sexual overtones already present in the alien in its head shape and the penetrating nature of its tongue and tail. The tubes are vaguely phallic and rigid, likely incorporated from the Necronomicon, a series of images drawn by Giger which the Xenomorph was heavily based on. Therefore, they may be a holdover from that creature's design.

Giger has said the tubes were added to balance the creature's design and make it look less human; they have no higher purpose in his mind.[citation needed]


Queens and PraetoriansEdit


A Praetorian

Queens have a variation of the dorsal tubes. Instead of actual, tube-like structures, spines run down it's back, numbering at six instead of four. Praetorians have a similar set-up along their spines, being genetically similar to a Queen Alien[9]. Breeding facehuggers also have these spines and go on to implant immature queens.[10]



A Predalien, lacking dorsal spines.

Some Predaliens shown also lack dorsal tubes, similar to the runner. However, Predaliens are not optimized for speed, being explicitly described as heavy assault units for the hive, so it is unknown why they lack the anatomy. Predaliens do not begin exhibiting back spines until the resident Queen forces them to evolve. Then, they begin to develop them with every successful battle and molting.
Cystic predalien

An evolved Predalien, with backspines.

While there is no known limit to a Predalien's molting strength, they can only grow 8 back spines, four down the left side of the back and four down the right. Interestingly, the back spines of a Predalien resemble that of a Praetorian and are the only ones to do so. It is unknown if this is just an aesthetic similarity or if there is anything more behind it.



The Dragon, a runner Alien.

Runner aliens completely lack spines, instead having a smooth back. This is likely so that the creature, more tuned into it's speed than its strength, is more aerodynamic, making it faster. However, this could be a side effect of a non-humanoid host.


Carrier model

An upgraded carrier.

Carrier Xenomorphs have specialized back spines, which have evolved to carry around the otherwise vulnerable Facehugger. Their spines shed nutritious material that Facehuggers consume.


  • In Alien: Isolation, the Alien's dorsal tubes can be seen vibrating from time to time when it stands still and is searching for the player. This may indicate the tubes are a sensory organ of some sort.[11]


  1. Aliens versus Predator: Extinction Bestiary
  2. Aliens vs. Predator: Three World War
  4. Shark Dorsal Fins
  5. Wolves hunting Caribou - Planet Earth - BBC wildlife
  6. AVP:2010
  7. Aquatic Life of the World pp. 332–333, Marshall Cavendish Corporation, 2000. ISBN 9780761471707.
  8. NatGeo, Fennec Fox
  9. Aliens versus Predator: Extinction Bestiary
  10. Aliens: Theory of Alien Propagation
  11. Alien: Isolation (2014), Creative Assembly, SEGA [Microsoft Windows, PlayStation 3, PlayStation 4, Xbox 360, Xbox One].

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