Staff Report: Are giant sci-fi bugs physically possible?

I’m not so sure about that. Arthropleura could grow over 8 feet long (longer than Eurypterid, which was reported as the largest arthropod in the article). I don’t know about you, but a giant carnivorous millipede would sure give me a scare.

Note that the arthropleura may well have been herbivorous. Still a pretty impressive bug, though.

I guess you could have even bigger bugs with major physiological modifications – like a real circulatory system and lungs – but how much could you change the anatomy before it was no longer an insect? If it developed an internal skeleton, I guess by definition it’d no longer be an arthropod.

And as long as you have an exoskeleton, there is the molting problem.

Archgallo, just so we know what we are discussing, it is a good idea to provide a link to the page that generated your post. Perhaps this is the one?

Welcome to SDMB!

Musicat, thanks. I realised last night after I shut down the computer that I should have provided a link. The one in your post is indeed the one I was referring to.

Baldwin, you’re right: it may have been herbivorous. Still, I wouldn’t let a bug of that size near me!

The non-intensive system of breathing is the main size-limiting factor for insect on Earth. It requires large ratio of surface area to volume, hence the small body size. In times of those giant insects the earth atmosphere was over 30% oxygen.

So it is either air richer in oxygen, or higher atmospheric pressure (2-5 fold would do nicely) - or the bugs would have to develop a better active air transport - something like air sacs in birds.

Also bigger creatures should have harder time flying (unless they learn to glide) so they have to have faster metabolism (and eat and poop more), be preferably at least partially warm-blooded- but the thermoregulation could develop for larger creatures.

This article reminds me of a sci-fi story I read this week that left me wondering… why are so many fictional aliens huge and bug-like, especially considering the trouble bugs would have with getting very large? I assume there’s a pyschological reason.

Vertebrates and arthropods are the only forms of terrestrial life with a half-way decent chance of evolving into tool-using, intelligent species, the cephalopods being, perhaps, a distant third.

I would guess because sci-fi writers often like their aliens to be, well, alien. We can empathise with human-like beings, mammals, and the like. Bugs are the most apparently un-human-like animals on the planet, both biologically and (for lack of a better term) socially. They already seem very alien and different.

The hugeness also works psychologically in that a human-sized (or bigger) threat is going to be seen as more impressive than a race of beings that come up to your ankles.

Ever seen closeups of bugs? Don’t they look much more frightening if enlarged than, say, a cat or dog? Their features are more foreign to us due to their evolutionary history.

Obviously no one here has ever played Earth Defense Force 2017. Most of the bugs are the size of a tractor trailer (spiders and ants). And of course the leaders are twice the size of a house.

I saw some of those as recreations on the Discovery Channel. Impressive. But the O2 level was much higher then.

That depends on how much time and change you are prepared to allow - If presented (out of context) with a specimen of our own very distant ancestors (say, some kind of wormy thing), I think we could be forgiven for being doubtful that it would ever evolve into something requiring a tool shed.

The bad guy in that noted documentary Men in Black was pretty big, when finally revealed in all his roachy glory.

I don’t think they used a real bug for that movie.

A fish-like thing appeared among the annelids one day.
It hadn’t any parapods nor setae to display.
It hadn’t any eyes nor jaws, nor ventral nervous cord,
But it had a lot of gill slits and it had a notochord.

 Chorus:
It's a long way from Amphioxus. It's a long way to us.
It's a long way from Amphioxus to the meanest human cuss.
Well, it's goodbye to fins and gill slits, and it's welcome lungs and hair!
It's a long, long way from Amphioxus, but we all came from there.

It wasn’t much to look at and it scarce knew how to swim,
And Nereis was very sure it hadn’t come from him.
The mollusks wouldn’t own it and the arthropods got sore,
So the poor thing had to burrow in the sand along the shore.

He burrowed in the sand before a crab could nip his tail,
And he said "Gill slits and myotomes are all to no avail.
I’ve grown some metapleural folds and sport an oral hood,
But all these fine new characters don’t do me any good.

(chorus)

It sulked awhile down in the sand without a bit of pep,
Then he stiffened up his notochord and said, "I’ll beat 'em yet!
I’ve got more possibilities within my slender frame
Than all these proud invertebrates that treat me with such shame.
My notochord shall turn into a chain of vertebrae
And as fins my metapleural folds will agitate the sea.
My tiny dorsal nervous cord will be a mighty brain
And the vertebrates shall dominate the animal domain.

(chorus)

    -- Philip H. Pope, ca. 1920

N.b., Amphioxus and the chordates generally are no longer thought to be directly related to the annelids. One might substitute “deuterostomes” for “the annelids”.

Nonsense. I bet the bug was a Culver City mechanic who showed up for work as an extra and they gave him an audition, which, obviously, he nailed.

An earlier thread that may be of interest, making some of the same points: http://boards.straightdope.com/sdmb/showthread.php?t=392004