Sorry for the double post, but a legitimate question just occurred to me.
What about centipedes and millipedes?
Yes, I know, strictly speaking, they’re arthropods, not insects. (Also, centipedes and millipedes aren’t even in the same taxonomic class: Chilopoda and Diplopoda respectively.) But biologically, they’re a lot closer to insects than crustaceans (Insecta, Chilopoda, and Diplopoda are all in the same phylum, Uniramia). I wonder how the structural issues are altered by (1) the addition of anything from a few dozen to a hundred more legs, thereby spreading out the weight more evenly, and (2) the distribution of internal organs (and therefore the spiracles as well) along a lengthy tubule instead of contained in one central body.
Aren’t there a lot of big centipedes and millipedes? A far higher proportion, I think, than of large ants, beetles, aphids, dragonflies, and the like. Britannica.com doesn’t mention the largest millipede, but they say the largest centipede is around a foot long. (Relax, Nancy. It’s in the East Indies.)
Not that I really want to visualize a millipede or centipede as long as my arm, but are they structurally more viable than, say, a similarly enlarged tick or crane fly?
Balance, your construction of a giant cockroach was extraordinary. Even I understood it. But I’ve got to tell you something about xploder. He’s a good friend of mine. We party on weekends. I know him quite well.
He’s not going to read your construction post and say “Hmmm. Interesting!” No. He’s going to say “Cool! Specs!”
Regardless of what you say, he will find a way to make it work. And he’ll make a girlfriend for that sucker, too. So thanks, Balance. You may have inadvertently ended civilization as we know it.
Well then…using the specs provided by Balance perhaps we can construct something in time for the annual summer Flint Dopefest! Then again, if I were to actually DO that, half the people would go “blech” and refuse to ever show up again so maybe not…
Seriously folks, you all have provided me with some SERIOUS answers and it is MUCHO appreciated! I once asked this question to a biologist that was working with us in the Army and he pretty much blew it off.
Concerning the centipedes and millipedes, Cervaise, I think that they would have a considerable advantage–they would remain recognizably members of their “type” than most insects. The distribution of the weight over more legs would be a big help, though at some point they would also require reinforcemant along their dorsal lines to keep from rupturing under the weight of the upper half of the exoskeleton (especially millipedes). Also, I think the legs would need to be vertical for RFH specimens. The cylindrical body is the most efficient for an organism with a spiracle respiratory system, I think–which may be why the largest documented flying insects (both in the fossil record and, IIRC, today) are dragonflies. Flying insects require more oxygen to sustain flight. The spiracle system would still impose a size limit on a cylindrical body, though; remember that the system essentially relies on air migrating through the tubes on its own–it’s only going to go so far. Tropical conditions seem to be better suited for this (and produce most of the large insects), but even with ideal temperature and humidity and current ambient oxygen levels they couldn’t grow beyond (SWAG) a few feet (see UberRoach, Spiracle Function In) in diameter without developing some lung-like structures. You could have a centipede or millipede of almost indefinite length, though. You get a lot more :eek: for your buck this way–to remain in proportion, a 3-foot thick millipede might be almost 36 feet long! (I’m having really bad feelings about that Flint dopefest now. ))
I wasn’t going to resurrect this thread, but now that it’s back on page one…<BLUSH> I’m glad you guys enjoyed my ramblings.
I don’t think we need to restrict our critter’s respiratory system to the spiracles mentioned above. Some arthropods do have something analagous to lungs.
fromSpider info
If we are increasing the size, I think we can increase the sophistication as well. The thread title said “insect”, but the OP merely said “exoskeleton”. Our hypothetical Arthropod Of Unusual Size might well have respiratory and circulatory systems comparable to higher animals.
True, mbh, we have focussed mainly on insects here. One of the common stipulations here has been that lungs (or an unreasonable facsimile thereof) would change the restrictions. The efficiency of the book lungs seems to present a problem, though. I’m not sure about the relative efficiencies of copper-based vs. iron-based blood (no comments from the Trekkie gallery, please ), so I’ll discount that for the moment. Possibly the book lungs could support a larger creature, but it would be restricted to relatively sluggish movement. (Particularly if it uses its blood pressure to move, or to facilitate movement.)
<Interlude>
“There’s a giant tarantula coming this way! Run for your lives!”
“Um…Walk casually for your lives?”
“Dude, is that thing moving at all?”
“Mommy, I’m boooored.”
“Take a nap, darling, I’ll wake you when it gets past that next car.”
“Don’t wanna sleep that long!”
“All right, just until it gets past the trunk, then.”
</Interlude>
If an arthropod developed musculature to force pressurized air over the book-lung plates, it would help. The structure still seems inefficient, though–lungs need maximized surface area, and flat plates aren’t ideal. Also, any kind of forced-air respiration is likely to require a measure of flexibility that could present problems with the (necessarily reinforced) exoskeleton. Hmmm…I wonder how solfugids breathe–do they use the same system as spiders?
I’m sorry I haven’t had time to read all of the thread so far, but I would like to make two points. Firstly, arthropods grow by moulting their cuticle and inflating a new, soft one which then hardens. An arthopod can only grow as large as it can survive with no skeleton at all. A land animal with a continuously-growing exoskeleton might be able to grow much bigger. Echinoderms like sea urchins are a potential example, but cannot live on land (or even in fresh water), and giant tortoises get along very well with a limited exoskeleton.
Second, I disagree with everyone else (including the experts) about the efficiency of a tracheal system. Large insects pump air in one direction through their tracheae, which permeate their tissues like vertebrates’ capillaries. Air has about the same oxygen content as oxygenated blood, but it has a much lower viscosity. So a tracheal system should be at least as good as a heart-lung arrangement. Diffusion is probably only a problem in the head (most large insects have relatively small heads, not counting horns and other decoration).
This point is bolstered by the observation that the largest insects are about the same size as the largest spiders and scorpions, which have lungs, and the largest land crabs, which have gills. If the tracheal system was a limiting factor, other arthropods could grow much larger than insects. Semi-terrestrial crabs probably have an advantage in that they can moult underwater, where it is much easier to support their weight.
First, I’m gonna create a self contained, hyper-oxegonated habitat. I’ll give it tropical weather, and plenty of food, with no predators. I’ll fill it with cockroaches. ( ok, maybe just a few. They’ll take care of the rest.) ooops, better make it an infintely expandable biosphere, or they’ll eat everything and starve. And now, for the piece de resistance, I’m gonna put it on the moon! Viola! I bet we get some pretty large insects now. Check back with me in a couple of million years.
The point being that there are practical limits to insect size on Earth, but BEM’s ( Bug eyed monsters ) COULD certainly evolve in a different envirnment. Sci-fi fans take heart!
Er, Dave, I think we were all kinda assuming the OP meant “here on Planet Earth”.
And you don’t want to hear what happened to the mouthful of orange juice I was working on just now when I got to the part about “…and fill it with cockroaches…”.
Besides, how can you have an “infinitely expandable biosphere”? The Moon’s a big place, but not THAT big. But I simply adore the idea of the Moon being populated by giant cockroaches. Would we be able to see them from Earth? They’d be much bigger than the lunar module which the Big Brains of GQ so annoyingly tell me we can’t see.
And what would they eat? Once their biosphere had expanded to fill the entire Moon’s surface, and they had eaten everything in sight, would we have to schedule regular rocket shipments of stale pizza and Wal-Mart dog biscuits so their “World Heritage Site” could continue?
Regarding the cat-sized prehistoric cockroaches: would a three foot fall be fatal to such a roach, as given in the tarantula example earlier in the thread?
My rules, I can have any kind of biosphere I want. Nya :p. You didn’t have any problem with Balance crawling through his giant roach, did you? Nooooooo. And, just think what I’ve done. Why, if this came to pass, we on earth would never have to worry about stale pizza crusts again!!! I’ll take my Nobel Prize now, please.
About your uberroach… Have you thought about the musculature you would need on that baby? I mean, if you’re talking about elephant-sized legs, with three-quarters of the thickness being chitin, where are you going to put the muscles to move those things? Insect muscle is different from mammal muscle (although I don’t know much about those differences other than some pretty scanning EM pictures), and the attachment points will all be different since the skelton (which the muscle needs to lever against) is on the outside, not inside. Hire an engineer.
Also, if you have lots of internal chitin struts for miscellaneous supports, how are you going to thread your muscles around them?
BTW: A turtle’s shell is NOT an exoskelton, the turtle has a perfectly good skeleton (made of bones) on the inside and the shell is not functional in terms of support or musculature.
As you can see, I have considered the musculature problem–and even allowing room for the tissue, the critter wouldn’t be able to move very well (see also my “When Giant Tarantulas Attack” post). I don’t recall the exact differences in tissue structure either, but IIRC most insects tend much more toward “quick twitch” muscles. They make very fast, jerky movements; if the uberroach could walk at all, it would be in tiny, twitchy steps, jerking each leg forward an inch or two at a time (because the twitch can’t accelerate all that leg mass enough to go very far).
Dave, your low-grav roaches might work, but they couldn’t come here. I think we can all be happy about that.
Max, I suspect the damage from a fall would depend on how the roach landed–if it landed flat on its feet, it would likely be OK. I’m sure that it could die from such a fall, though, particularly if it landed on an uneven surface. Three-foot falls aren’t universally fatal among large tarantulas either, I don’t think.
Sorry for ressurecting this but I filt I needed to chime in.
When I was at the Cambridge Geological Museum or whatever the heck it was and took a tour a grad student was particularly proud of a fossil they found.
It was the body of a spider, about 3-3.5 ft long and maybe a foot wide.
He then said that based off of the proportions of current spiders it would be about 7-8 in diameter w/ legs.
Not at all–never apologize for bringing the UberRoach thread down out of the attic. I think I speak for all of us when I say that it’s one of our favorites.
Centipedes can grow to a foot long, so can a few species of stick insects (Phasmida). But at this size, the limits of a chitinous exoskeleton are already apparent. Both are relatively soft-bodied (though a foot-long centipede has no problem defending itself) and live in tropical rainforests, where dessication is not a problem.
Centipedes can grow to a foot long, so can a few species of stick insects (Phasmida). But at this size, the limits of a chitinous exoskeleton are already apparent. Both are relatively soft-bodied (though a foot-long centipede has no problem defending itself) and live in tropical rainforests, where dessication is not a problem.
), so I’ll discount that for the moment. Possibly the book lungs could support a larger creature, but it would be restricted to relatively sluggish movement. (Particularly if it uses its blood pressure to move, or to facilitate movement.)
