Spiders in Space

Oh, the nerdity of it all. I just read about a discussion of how spider-aliens would survive in space. This is my kind of thought-experiment!

In my stellar empire, the sapient life of the home world are arachnids. Due to an oxygen-heavy world with certain evolutionary characteristics, spider-like beings developed intelligence and formed society, leading them (eventually) to start looking toward the stars. This led to the development of space suits for the pioneering arachnid astronauts.

What would these look like? How would space suits be differently designed to support arachnids?

Let us posit that the arachnids are roughly 4 feet from “spinneret” to fangs. Their legs are large enough to support them (I don’t know what that is). They’re light compared to us (maybe 25 pounds at the heaviest – bear with me on the whole square cube law deal). They have roughly equivalent technology levels to ourselves at the time of our first missions into the stars.

Just by coincidence, I’ve been reading up on spider physiology recently, so this piqued my interest. Most of the answers in that thread are pretty good.

I’d first have to state a caveat: multi-legged alien beings evolving on a distant planet will not be spiders. It’s unfair to compare limitations and abilities that they have to those of terrestrial spiders — they aren’t related! Just blowing up an Earth spider to 1.2 meters long is not a valid comparison. But OK, let’s play a game and imagine an alien “spider” that evolved from an ancestor living in a similar niche to that of our spiders. Traits that are probably relevant are:

  • Obligate carnivory. It’s a predator with a need for live food. Unless there’s a way to store frozen bug juice shakes that this species will willingly eat, this sounds like a big problem — space-faring “spiders” are going to have to bring along along bug ranches to maintain livestock. And food for said livestock. Forget the spacesuits, there are going to be some demanding requirements for life support on space ships.
  • External digestion. Why, you might ask, would they need live food? Spiders inject enzymes into their prey which break down the guts of the animal into a liquid soup that they can slurp up. The food is both the container and the meal. “Spider” Tang is going to be a tough recipe.
  • Ambush predator. This has pluses and minuses: most spiders have notably lower metabolic rates than other poikilotherms, about 70% of what is expected in animals of equivalent size. So, lower oxygen consumption — that’s great for spacecraft/spacesuit design. On the other hand, they can have extreme surges in activity, for instance, when prey is captured. Oxygen consumption is going to be somewhat unpredictable.
  • Pulmonary system. The linked discussion mentions how spiders often have a dual respiration: they have two or four book lungs in the ventral abdomen, but also many of them have a trachaeal system, an array of small tubes that penetrate the cuticle and permit atmospheric gases to flow in to the tissues. This one might not be a problem, though: trachaeal systems are less and less effective the larger the animal, and they rely more on discrete respiratory organs, like lungs, as they grow to a larger size. At 1.2 meters long, these alien “spiders” are almost certainly going to have “lungs” and “nostrils” — it’s just that if they’re like our spiders, they won’t be on the face, but low on the abdomen.
  • Respiratory pigments. This is where it becomes obvious that you can’t simply extrapolate from Earth spiders to space “spiders”. Our spiders use hemocyanin to carry oxygen, which has a significantly lower O2 carrying capacity than our hemoglobin. You’d think along the way to evolving larger size and metabolically demanding intelligence they’d have to be using a more efficient respiratory pigment…although blue-green blood is kind of cool.
  • Sensory apparatus. Look closely at a spider sometime: they are covered with hairs. These aren’t dead insulators like our hairs, either, but are all invested with nerves for mechanical and chemical sensory functions. Putting them in a suit that limits them to only visual input is going to be like dumping them into a sensory deprivation tank.
  • Motility. There is a suggestion that they could use “an enclosed pod that the spider can sit inside with legs folded and have mechanical arms/legs that support the pod and allow it to walk around.” Maybe. But that throws away many of the virtues of a space-walking “spider”. They are incredibly agile, are accustomed to maneuvering in 3 dimensions, and are beautifully adept at manipulating objects in their environment. Watch one wrap a prey item in a web — they are weaving with all 8 legs simultaneously, flipping it around and dancing about delicately. It would be a shame to limit that by stuffing the “spider” astronaut in a barrel and making it manipulate its environment with a few waldos.

It’s a fun exercise, but if we ever find such a creature I suspect it will have less similarity to our spiders than we humans do to an acorn worm, so much of the speculation is moot.

Real spiders are more interesting. As I said, I’ve been reading up on spider physiology, so here’s a diagram of the main elements of the spider circulatory system (“h” marks the heart, on the dorsal side of the abdomen.)

That’s the cartoon version — here’s a resin cast of the full circulatory network of the opisthosoma of Cupiennius. It blows me away that they were able to do this — Cupiennius is fairly large as spiders go, but still pretty tiny.

Even more impressively, people have measured the blood pressure in the spider circulatory system — no, not with an itty-bitty sphygmomanometer. I suspect they used optical methods to visualize pressure changes, but that’s a paper I haven’t tracked down yet.

Systole and diastole are still valid concepts in a spider. In case you were interested, their hearts beat at a rate of 9 to 125 beats per minute. That’s quite a range, but as I mentioned above, one of the challenges is a highly variable metabolic rate.

Ultimately, though, if you’re going to design an SF “spider”-like alien, you shouldn’t be constrained by the form and physiology of terrestrial spiders. A homeothermic creature with an endoskeleton, but with a bunch of limbs and eyes and a sclerotized cuticle, and maybe some funky spiky complex mouthparts, is going to look enough like a spider to Zapp Brannigan that that’s what he’s going to call it anyway.

Schmitz A (2016) Respiration in spiders (Araneae). Journal of Comparative Physiology B 186(4):403–415.

Wirkner CS, Huckstorf K (2013) The Circulatory System of Spiders. In: Nentwig W. (eds) Spider Ecophysiology. Springer, Berlin, Heidelberg.


  1. brett says

    Do you think an eight-limb body plan could become dominant among an alien world’s vertebrate equivalents, in the way that the “four leg plan” kind of did with ours? I’m wondering if it’s just pure chance and path dependency, or if biomechanical efficiency would favor creatures with lower-limbed body plans when it comes to getting bigger?

    Ultimately, though, if you’re going to design an SF “spider”-like alien, you shouldn’t be constrained by the form and physiology of terrestrial spiders. A homeothermic creature with an endoskeleton, but with a bunch of limbs and eyes and a sclerotized cuticle, and maybe some funky spiky complex mouthparts, is going to look enough like a spider to Zapp Brannigan that that’s what he’s going to call it anyway.

    Pretty much. If I saw an alien with eight slayed limbs around a squat torso and a head with multiple sets of eyes plus strange looking jaws, it’d be close enough for the nickname to stick.

  2. says

    Spiders inject enzymes into their prey which break down the guts of the animal into a liquid soup that they can slurp up.

    And that’s why criminals should fear Spider-Man.

  3. monad says

    When people are in a space suit they lose all chemical and tactile interaction with the outside world, too, and we make do with the mobile sensory deprivation tanks. I suppose it would be worse for a creature that depends entirely on them, but anything that could build such a suit is probably going to have developed decently high resolution vision too.

  4. A momentary lapse... says

    Portia might be an interesting jumping off point for how to do an intelligent spider. Not sure what the current state of research is, but they seem to show fairly remarkable (though slow) planning abilities in their hunting strategy despite having low neuron count. Trading off speed of cognition versus resources needed might provide an advantage for a spacefaring species that can spend a lot of time “idling” while travelling between destinations.

    Peter Watts did something to this effect in Echopraxia.

  5. says

    IIRC, the aliens in Vernor Vinge’s A Deepness In The Sky were arachnoid, living on a world with a highly elliptical orbit that took it far from its parent star and into ice ages that they had to hibernate through. It’s been a while since I read it though.

  6. Gregory Greenwood says

    Tabby Lavalamp @ 3;

    And that’s why criminals should fear Spider-Man.

    It does put a rather dark spin on the line from the old Spiderman theme song “Spiderman, Spiderman, does whatever a spider can”, doesn’t it? Especially since there are species of spider which aren’t exactly opposed to a little light cannibalism here and there.

    It jut goes to show that Spiderman could work just as well as a horror franchise instead of superhero story.

  7. Gregory Greenwood says

    I am now amusing myself by imagining first contact between an advanced civilisation of arachnid aliens with come similarities to terrestrial spiders and humanity, where the arachnids hail from an enlightened, post-scarcity, Federation/Culture type civilisation. We are terrified by their appearance (even people who aren’t arachnophobes might by discomforted by a being that looks like a human sized spider) even as they are horrified by our continued barbarism. Plenty of opportunity for a little commentary on the human tendency toward knee-jerk xenophobia and the ongoing failings of our species to live up to its moral aspirations.

  8. nomdeplume says

    People never think clearly about aliens. There was no inevitability about spiders being an important group on Earth. The original speciation event in which the ancestor of all spiders evolved might have easily come to nothing as a result of some climatic event etc. Conversely there are millions of speciation events which might have started something but didn’t. There might be chance superficial similarities between alien species and some Earth species, but that is all they would be.

    I similarly get annoyed by the often stated idea that species living in extreme environments on Earth tell you about potential for life elsewhere. No, they only exist here because of the huge pool of other species from which extreme adaptations can evolve.

  9. Callinectes says

    It seems to me that a spider is going to lose the sensory inputs from its body hairs in a vacuum whether it is in a suit or not, so that won’t factor into the design.

  10. says

    PZ – If you haven’t read it already, you may enjoy a book called Children of Time by Adrian Tchaikovsky. It involves artificially uplifted spiders evolving on a planet as the apex species. I thoroughly enjoyed it, it’s a really entertaining sci fi novel that also involves humans and rogue AIs, but mostly intelligent spiders evolving and the evolution of their society.

  11. says

    Being oviparous means they could travel by mailing an egg-sac, to be quickened robotically as a ship approached its destination. Human live births cause all kinds of headaches for long distance/time travel because you need to ship a uterus and a woman to carry it. As I have noted elsewhere, testicles are wasted luggage for space travel, especially colonization.

    So a deep-time spidership looks like a frozen egg-sac and a robotic egg timer. Huge win for spiders!

  12. John Wilkins says

    It’s pretty obvious how to do an arachnosuit: Just replace chitin with some sort of polymer that will retain pressure, and then electroplate the exoskeleton so they are able to reflect heat.

  13. says

    You could rig up some system to stimulate those mechanical sensory hairs, maybe rig it up to a radar array? I have an altered hominid species in a game concept of mine that uses modified vibrissae as an interface system for their tech.

  14. Artor says

    Conversely, I had an idea for a sci-fi alien race of sentient cephalopods. While the creatures themselves are boneless, they learned to build armatures that they could manipulate and allow them to walk upright and use leverage, like an octopus on stilts. If we grant them the same abilities as, say, a mimic octopus, one could even imagine such a creature being able to pass for humanoid. They would probably develop a more leathery skin to allow them to function out of water for longer. Unless they developed lungs, their communication might be by shifting color, or gesture, or who knows what?

  15. Artor says

    As for the obligate carnivore with external digestion problem, I’d think an advanced race of spiders with modern technology could come up with some kind of bottled bug juice they could stockpile or synthesize. Sure it would be more complex than Tang, but so is a cheesecake. I can see a Starbugs on every corner in downtown Spiderville.

  16. unclefrogy says

    well intelligence as exemplified by humans gave us an obvious survival advantage we have little else that set us apart from other primates that are not a weaknesses.
    Looking at the spiders that live on earth they seem to have very successful survival abilities without any obvious need for some form of higher level intelligence.
    I have a hard time imagining some alien intelligent that realistically does not share our comparative weakness and strengths but maybe not our humanoid form.
    space monsters are somewhat easier to make up. just let the old Id take over the thinking.

    uncle frogy

  17. says

    Spiders do have a few “legs up” on us in the astronaut department with 8 legs inside a hard exoskeleton they have the makings of a pretty good space suit. I know they wold have to seal up their trachea and enclose their soft abdomen and book lungs somehow but their exoskeleton is sort of partially pre-adapted for space.

  18. says

    I’ve been working on a sci-fi novel involving first contact with aliens — radio signals, not space travel, no FTL — and while I’m still struggling with putting together an engaging plot (the aliens are essentially a very important B plot, with Earth’s eco-socio-political system furnishing the A plot), I’ve got some ideas lined up for the aliens.

    The species that’s most fleshed out: vaguely analogous to an Earth millipede, in that they’re descended from detritivorous ancestors with lots of legs arranged in pairs around body segments. However, they had a dietary shift millions of years ago to a mutualistic relationship with a protein-rich fungus-analogue that parasitizes the local tree-analogues, which they now farm as their main food source. In the process, they’ve grown much larger: roughly four feet long as adults, 8 inches diameter (give or take), internal lungs, a closed circulatory system, an endoskeleton developing from calcium stores in their ancestors’ nerve cords, a dramatically thinner and softer exoskeleton, specialized forelimbs that function as hands, fingers, and/or mouthparts as needed, and a reproductive strategy of ovoviviparous hermaphrodism with high investment in young and polygamous communal child-rearing.

    They’re unique among the Milky Way’s known sapients for being the only wholly non-predatory technological species — it takes a lot of protein to be able to afford a big brain, and all of the other half-dozen-ish known sapients got there via carnivorous or omnivorous diets, i.e. hunting things that were only slightly less intelligent than they were. Combine that with a relative lack of predators in the “millipedes” evolutionary history, and they have the most radically different psychology in the backstory, both from humans and from the other sapients in the galaxy. (I’m still working out the details of how their psychology is different, but they’re definitely very chillax in the face of problems and have very little sense of urgency, are inclined to take the long view, but also tend toward double- and triple-checking their work with a perfectionism that humans would consider pathological — they’ve been farming those goddamn mushrooms for hundreds of thousands of years, by gum, and they’ll be damned if this year’s crop is going to be ruined by some interloping infection because the relative humidity was wrong.)

  19. pgmoni says

    To PZ I’d question your premises 1 and 3 : in order to become social, you might think that spiders should have had their
    agricultural revolution and have gone beyond the stage of hunter-gatherer. Which they might well do, since there is at least one vegetarian species on earth, Bagheera kiplingi.

  20. lakelover says

    I’d like to second the Children of Time recommendation. I’m no expert but I imagine that Adrian Tchaikovsky plays pretty fast and loose with the ‘science’ by the time the book reaches its totally bonkers ending. But a book that can have me rooting for giant space spiders has definitely got a lot going for it! It was great. I also loved Dogs of War by the same author, which brilliantly explores the perils of battlefield AI and a host of other potential issues around tech that could be just around the corner.

  21. anfaith says

    My son was in a First Lego League robotics team this year and the theme was space. His small team of 7th-graders studied multiple aspects of living in space. Since the coach was a professional entomologist, she made sure one of the things they looked at were Bugs In Space!! (this was always said with great emphasis).

    One interesting thing they learned was that spiders initially have difficulty weaving webs in microgravity, but eventually get the hang of it and figure out how to make a go of it. https://www.space.com/11818-space-spiders-weightless-webs-station-shuttle.html

    They also got to visit a research team trying to identify genetic strains of plants that can grow without the gravitational cues that normally tell plants at which end to put the leaves and at which one to put the roots. But I thought the spiders were cooler.

  22. DanDare says

    The bug juice problem is probably one of preservation. We humans had to solve that too. Each spider would inject and then preserve in personalised bundles. Or there could be a synthetic venom that could be shared by many individuals when time to ingest.

  23. Chris Capoccia says

    lots of interesting details… comparing 9–125 bpm to humans, i don’t know enough of why I should be surprised about the range. many human athletes have resting heart rates below 40 and younger athletes can have max hr above 200.

  24. says

    I don’t think we will meet spiders (like our earthling ones) in space, but not for physiological reasons. Their feet and claws are not fit for manipulation things, nothing like fingers. Once intelligent enough they could overcome this limitation but that’s an chicken and egg problem … They shouldn’t be able to develop the kind of intelligence needed (usage, manipulation, building of objects) with their kind of legs.
    But never underestimate a spider … Bagheera kiplingi isn’t the only spider with a taste for plants. We met another one while working on a carnivorous ant-plant (Nepenthes bicalcarata & Camponotus schmitzi) in Borneo: Orsima ichneumon. This jumping spider also feeds on nectar (as has just been published), but we were blind for it. I wondered why it was so often living on our ant plant, but found no connection. For I knew spiders never eat plants …
    So we’ll see whom we find on the other side of the moon. They are much older than we are …

    Still I would rather expect another eight legged creature: the octopus! Intelligence and hundreds of “fingers” should be a good starting point. Sadly the ocean is not, as you need fire for nearly every technology needed on the way.
    But I have an idea, I have to write it down …