A squid-like organism uses gravity powered flight but relies on jet propulsion for launch, pouncing, and evasive tactics.

It’s aerodynamically based on the way a true squid flies however it has evolved atmospheric jet propulsion to replace the constricting hydraulic jets.

Real squid currently fly like this, with water jets:

flying squid

I have already found a solution to cooling so it can now fly like this:

But it needs to charge the conflagration chamber then ignite it quickly after leaving the water. That timing is a different question; this one focuses on a gland or faculty that generates and manages the ignition chemistry.

About the creature:

It’s tentacles and fins have become much larger for sustained flight, two tentacles have become wings with a 10-foot wingspan (4 foot wings) which lock in their extended position when they jump out of the water. It’s other arms remain articulate for grappling and marine locomotion.

The jet deflagration chamber is the scavenged nearly perfectly flared cylindrical exoskeleton of another mollusk, with a diameter acoustically tuned to an OH deflagration cycle. This squid binds it to its body, having an intake on the nose and exhaust from the posterior of the animal. The material is unlikely keratin or calcium carbonate, it needs to have good thermal insulating properties and structural integrity.

The jet fuel is twofold: H gas is a natural fermentation byproduct stored in bladders; a symbiotic algae lives in a layer under its translucent skin, consuming its respiratory exhaust and producing O$_2$ which collects in another bladder. The two gasses are injected into the unvalved deflagration chamber for propulsion.

The jet only needs to run for 2-second bursts of possibly 8 - 12 pulses. It’s purpose is to simply gain enough momentum to get airborne, or evade a predator while in flight.

Assume the animal’s total gross weight is 5kg, and it can accelerate at 8 ms$^{-2}$ for two seconds. This flight is expensive, like a jaguar's chase, so they try not to waste this flight. Recharging their jet can take hours, or days without the right conditions.

Given the 960J of heat generated by this reaction, as calculated by Starfish Prime, and the 2-second burst requirement to reach cruise speed;

What biological ignition system could spark the O$_2$ & H fuel pulse jets most reliably?

The spark can be from chemistry synthesized by the animal, or generated by a symbiotic relationship, or harvested from the environment; but it must be a true exothermic ignition reaction.

  • 3
    $\begingroup$ There are already questions on how dragons can ignite their mix with a spark. What's unsatisfactory there? $\endgroup$
    – L.Dutch
    Feb 18, 2022 at 4:25
  • $\begingroup$ Is there something special about igniting hydrogen and oxygen that renders the other answers useless? $\endgroup$
    – sphennings
    Feb 18, 2022 at 5:04
  • $\begingroup$ @VogonPoet sorry but any question with "creature-design" and "hard-science" is a problem, imho. Hard-science doesn't require a creature to exist, but it requires a known RL principle: scientific references are required for hard-science answers. see banner. You can't calculate how big a spark my antimatter could yield, or provide evidence LDutch' piezo can be done biologically. It does not happen in Earth's nature. You may wait for a hard-science answer here, but I actually expect a (science-based) frame challenge instead... it may be impossible to achieve hydrogen ignition inside a body. $\endgroup$
    – Goodies
    Feb 18, 2022 at 18:26
  • $\begingroup$ @Goodies who asked for jet propulsion? I’m igniting real-world gas by a chemical means known to science. A simple calculation of gibbs free energy and configuration. I could have used the propulsion tag earlier however, and will edit that post. $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 20:53

5 Answers 5


The fish can grow a piezoelectric crystal next to the ignition chamber, and compress it with some muscles, so that it produces a spark in the mixture.

Most materials exhibit at least weak piezoelectric responses. Trivial examples include sucrose (table sugar), DNA, viral proteins, including those from bacteriophage. An actuator based on wood fibers, called cellulose fibers, has been reported. D33 responses for cellular polypropylene are around 200 pC/N. Some applications of cellular polypropylene are musical key pads, microphones, and ultrasound-based echolocation systems. Recently, single amino acid such as β-glycine also displayed high piezoelectric (178 pmV−1) as compared to other biological materials.

Basically and simply the same mechanism working in a gas lighter.

enter image description here

And hydrogen mixed with oxygen is just waiting for an excuse to lit up.

  • $\begingroup$ How does he crystal get into the scavenged shell and what natural high-voltage conductors could be used for the spark? This sounds like it required a rigid hammer to strike the crystal. I don't see this coming from biological processes, is there an example? $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 6:09
  • $\begingroup$ Wait… This is real? So.. like the Mantis shrimp hammer plus this = spark? It would need a spark gap right? $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 19:44


Hydrogen and Oxygen mixtures will spontaneously ignite under pressure, just like the derv or fuel-oil in many cars and trucks without any spark necessary.

Now, in diesel engines the pressure must reach as much as 24 atmospheres, but the much more dangerously flammable mixture of gasses here need much less, perhaps 12 Bar as suggested here, maybe even less.

  • Compression in a pouch or chamber.

A muscular chamber where the two gasses are mixed can be contracted with a squeeze of muscular-effort, resulting in the spontaneous ignition of the gasses and a pulse of plasma which begins the continuous flame process producing thrust. (As if they'd lit their own farts, no lighter/matches necessary).

  • Sound pressure ignition.

Alternatively, a whistle or short "beep" achieving 215 dB (very, very loud) is equivalent to 12 Bar and achieves the same effect with a different mechanism and gives them a bit of an audible signature to-boot.

  • $\begingroup$ This looks like a good base for a solution. For the hard-science part, can we find numbers on the ignition point for this fuel? An interesting concept I considered for ignition is the implosive collapse of cavitation bubbles. These collapse to form microscopic hot spots which have been measured at 5,075° $\pm $156K. But can such a small hotspot ignite the reaction? $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 6:02
  • $\begingroup$ I did the best I could to find figures, as you see the 12 Bar number comes from a weird mixture involving Nitrous Oxide. From experience, but not by evidence, O2 is as good for ignition, but the Nitrous produces more by-gassing of Nitrogen. The 215 dB is by calculation and close to the limit possible in air I believe. I've not time now to look into it further as sleep beckons, but maybe tomorrow. @VogonPoet $\endgroup$ Feb 18, 2022 at 6:07
  • 1
    $\begingroup$ @EveninginGethsemane I managed to find an abstract of an article that states hydrogen can auto combust at 3.5-7Mpa (35-70 bar). The web address is a bit long to post, just look up "Autoignition of hydrogen at high pressure - ScienceDirect" $\endgroup$
    – Sonvar
    Feb 18, 2022 at 17:24

Mantis shrimp are capable of generating a force of at least 1000N with their hammer-like appendages. If the animal had such a mechanism internally it could use the force to strike a natural piezoelectric crystal as suggested by L.Dutch and generate the spark needed to ignite the gas

Alternatively, if the force could somehow be applied to gas contained within a confined space, the pressure alone could be used to ignite it. According to this paper hydrogen gas can undergo ignition at about 3.5MPa of pressure, but to generate that the 'hammer' would have to hit a lot harder, which could be enabled by larger muscles since this squid seems be a much larger creature than a mantis shrimp, and/or by the impact happening in a very small area, just enough to create a spark.


Animal produces a (likely hypergolic) starter, that ignites the hydrogen.

(This is very similar to how some rocket engine starters work.)

Said starter can be relatively expensive to generate, as you only need enough to ignite the reaction. (This would work better if the duration was longer.)

As to which starter. My immediate idea would be hydrogen peroxide (and a catalyst), which works nicely with hydrogen. (H2O2 breaks down into high-temperature steam and excess oxygen, which should be enough to ignite the hydrogen.)

Main issue here is that yes, there are biological sources of H2O2, but not high-test H2O2. (That I know of.)

(Also, it does somewhat beg the question of 'if you're already making H2O2, why bother with switching over to pure H2'.)

  • 1
    $\begingroup$ That’s a good idea. As to the question, you answered it. H2O2 is less common that H2. Hydrogen peroxide is what causes our hair follicles to loose their pigment later in life, btw. It’s a naturally occurring product in small quantities. H2, as stated, results from fermentation as well as the symbiosis. Again, it’s a 2-second burn a couple times per day maybe. $\endgroup$
    – Vogon Poet
    Feb 19, 2022 at 20:36

A mineral swallowed by the animal will yield the spark

A little known fact about the above animal (and dragons) is they chew, or swallow certain crystals when they need a spark. In the mouth, the chewing of the crystals will yield a spark for ignition of the dragon's famous breath of fire.

Dunno about flying squids, but dragons fly forward, also when using jet propulsion

Your squid-like animal seems to be designed in reverse. I can only explain it for certain dragon species. In the case of jet propulsion, the mineral is part of the dragon's excrements. Stomach acids will dissolve the minerals the dragon swallowed, yielding a considerable spark coming out of the stomach, near its hydrogen container organ. The organ will start blowing hydrogen over the spark, which ignites it.

Scientific explanation for this

The cracking/dismantling of the crystal will result in freeing up a few particles of antimatter, which were kept confined in the crystal lattice by electromagnetic forces. When the lattice is destroyed, the antimatter particles will immediately annihilate and yield the spark. Dragons are a protected species nowadays, so I can't reveal the mineral.

"Other applications work best with confined antiparticles. Because antiparticles suffer annihilation when they come in contact with matter, they must be confined in vacuum, typically in an electromagnetic trap."


  • 1
    $\begingroup$ I don’t think antimatter containment—or even generation would be feasible for an organism? $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 19:45
  • $\begingroup$ Only a few particles are needed :) it's an ignition, just a little spark is needed. My speculation is particles of antimatter could be contained in certain crystals. You propose igniting hydrogen inside a creature.. there's no science, this is all fantasy.. that's why I put my answer. We could upvote eachother, when you would appreciate a non-scientific answer. Suppose you would use these creatures in your story.. would any reader of your story expect a hard-science explanation for these alien animals ? They just need to believe it, as plausible. Proof is not needed. $\endgroup$
    – Goodies
    Feb 18, 2022 at 23:47
  • $\begingroup$ Every living thing has hydrogen. We are all made of hydrocarbons. That’s not fantasy. Can you give a hard science example of anything with antimatter in it? And “what” antimatter? A positron? $\endgroup$
    – Vogon Poet
    Feb 18, 2022 at 23:49
  • $\begingroup$ @VogonPoet I upvoted your first comment. It depends on the crystal. The mass of both annihilated particles will translate into e=mc2 energy. Whether that yields a spark, or a valuable ignition I have to hand-waive, I'm not a physicist. About hydrocarbons: it is very difficult to harvest molecular hydrogen from hydrocarbons, these substances are to be "cracked" first and that will cost energy. Maybe it will be more difficult finding a plausible explanation for the hydrogen needed, compared to ignition.. the amount of hydrogen needed for your biologic pulse-jet deserves a separate question. $\endgroup$
    – Goodies
    Feb 18, 2022 at 23:58
  • 1
    $\begingroup$ As the question states, microalgae or cyanobacteria break water into oxygen and hydrogen. Done. Now, about those positrons? Where does a squid find one in the ocean? $\endgroup$
    – Vogon Poet
    Feb 19, 2022 at 0:13

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