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I've been conceptualizing a species of intelligent insects. They would have 6 limbs, they can fly, but they walk bipedally. I've been thinking of having them get down on all limbs of they need to go fast and can't fly away from something, but I do want them to be at least mostly bipedal.

Here's my problem though: I can't find anything relating to insects walking bipedally, and I don't know where I should look as far as anatomy I can adjust to work in this situation.

How can I make a bipedal insect?

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    $\begingroup$ I would start with an insect like the Praying Mantis, which already walks on 4 legs and has specialised the front two. $\endgroup$ – Lee Leon Oct 10 '17 at 6:37
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    $\begingroup$ do dung beetles count? $\endgroup$ – user6760 Oct 10 '17 at 7:48
  • $\begingroup$ @user6760 great point, if the roach getting propped up by air resistance counts so does the dung beetle. $\endgroup$ – anon Oct 10 '17 at 20:42
  • $\begingroup$ Not an answer, but man, seeing your questions has really made me wish to read/see your final work. $\endgroup$ – Jayro Boy Neto Oct 11 '17 at 2:24
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Cockroaches can run bipedally.

J. exp. Biol. 156, 215-231 (1991) MECHANICS OF A RAPID RUNNING INSECT: TWO-, FOUR- AND SEX-LEGGED LOCOMOTION BY ROBERT J. FULL AND MICHAEL S. TU

bipedal running cockroach

image from http://www.berkeley.edu/news/media/releases/2002/09/rfull/locomotion.html

(Another wacky congruence between the bug world and ours: At top scuttling speeds, the roach actually rears up on its hind legs — which are longer than its front and middle pairs — and runs upright, like a human sprinter. The roach is also the world's fastest land insect, able to run the human equivalent of 200 miles per hour, as Full's students relished informing the Guinness Book of World Records.)

Interestingly it is when the roach is really running fast that it goes bipedal. Bipedal is its top gear. Look how far forward it is leaning.

I must say that I was disappointed I could find no videos of the cockroaches running bipedally. Dr Full, time to represent for your lab!

In any case - high speed 2 legged cockroaches. Maybe your bipedal bug goes everywhere fast. It occurs to me that an insect with wings could extend them to offer resistance against the top of the body falling forward (at the cost of some speed). Wings would be a good way to brake too.

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  • $\begingroup$ I suspect that the roaches shape is providing enough air resistance to lift it up like that. I don't know which species is in that test but many also have wings. $\endgroup$ – anon Oct 10 '17 at 21:01
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    $\begingroup$ 1 more reason for me to hate those things. $\endgroup$ – Virusbomb Oct 10 '17 at 21:19
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Short answer
Insecta are not designed for bipedal locomotion.

Background
The trick of insecta is that six legs allow for locomotion while keeping 3 limbs on the ground at all times (Fig. 1). This tripod gait is the direct results from having six appendages (Lanham, 1951). Importantly here, locomotion of a small animal encased in a rigid exoskeleton is not effective with less than 3 pairs of legs. Insects generally walk by lifting the two outer legs on one side and the middle on the other side, sweeping them forward and placing them down together. Hence, insects support their rigid structures with a tripod at all times. Tripods are among the most stable configurations, and they never wobble (why on earth do tables have 4 legs?) (Lanham, 1951).

Note that the praying mantis is stationary when praying (hunting) while it uses all six extremities when moving around. The dung beetle is a fascinating exception; when rolling a ball of dung it indeed appears to use just two legs for walking and four to roll the dung (Fig. 2); however four legs are also in constant contact with the ball so the tripod is still in effect, albeit on two different planes in this exceptional insect. Moreover, they 'cheat' by using their head for balance to (Fig. 2).

Further, while acknowledging the fallacy inherent in thinking that an absence of evidence is not evidence of absence, I couldn't find evidence that insects have a vestibualr system, or an equivalent control system of balance.

In mammals for example, the inner ear houses the vestibular system that registers acceleration in any direction through the semi-circular canals and the otolith system.

In all, given their rigid exoskeleton and the absence of a balance system as far as I know, I would reckon that insecta are simply not designed for bipedal locomotion.

One of the answers mentions running cockroaches; indeed they do, as do some species of lizards when in danger. This, however, is a matter of short bursts of rapid locomotive activity and is not their regular way of moving. The bipedal gait is simply maintained through speed and cannot be sustained for a long time and cannot be used other than sprinting away in a more-or-less straight line.

tripodgait
Fig. 1. Insects' locomotion resembles a double tripod. Insects have a cyclic gait which consists of two phases, the stance phase and the swing phase. The stance phase is the power stroke, it pushes the body forwards in the direction of travel while the leg remains on the ground. Three legs are used is this phase by forming a tripod with the front leg and the hind leg on one side of the body and the middle leg on the other side. This formation is why this gait is known as the tripod gait. Source: Insect robotics.

DungBeetle
Fig. 2. Dung-rolling beetle. source: Phys.org

Reference
- Lanham, Science (1951); 113(2946): 663

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Bipedal motion is semi rare in the animal kingdom

few mammals can even do it, and even fewer are purely bipedal (humans and kangaroos). Few reptiles ever managed it and they mostly went extinct (except the Jesus lizard). One common pattern between all of them is specialization or minification(T-Rex) of upper legs into arms and specialization of lower legs into more robust and capable legs. With this in mind there are some examples in the insect world approaching this trend.

Grasshopper

Grasshopper These guys have specialize rear legs capable of propelling their whole body forward great lengths under their own power. If they were to walk bipedally these legs could provide the strength to do so.

Praying Mantis

praying mantis

Here you start to see the erect posture of bipeds and the specialization of forward legs into arms.

So to answer your question one way. You could view the combination of the mantis and grasshoppers traits to come up with a structure capable of bipedal motion. This isn't feasible for insects simply because jumping and flying are often more easily achieved and offer more range and capability, but it is physically possible.

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    $\begingroup$ The manis is a great demonstration of why bipedal insects wouldn't happen, because of the fact that they have six legs to start with. The specialisation of the forward legs into arms has happened, but it still has four legs to walk on. I don't think bipedalism would happen unless you can find a plausible reason why they'd need all four front limbs for something other than walking. And as much as we'd all love to have an extra pair of hands sometimes, I don't think using all four forelimbs as arms would be a sufficient evolutionary advantage over two to outweigh the greater difficulty walking. $\endgroup$ – Simba Oct 10 '17 at 14:22
  • $\begingroup$ I never said it was naturally possible, bipedalism doesn't offer instects much because of their size. flying and jumping offer them far more. I was only describing the progression of traits to conceptualize a possible version. $\endgroup$ – anon Oct 10 '17 at 14:26
  • $\begingroup$ yes, I was agreeing with you. :) $\endgroup$ – Simba Oct 10 '17 at 14:29
  • $\begingroup$ @Simba But on your point, it could be that 1 set of arms is evolved for attack like that mantis while another set evolves hands for detail work. Our own form lacks a purely offensive structure. $\endgroup$ – anon Oct 10 '17 at 14:32
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Don't worry so much about what terrestrial insects look like. You're "evolving" something from those critters. So, let's look at the first problem: what do you need for bipedal locomotion?

Balance

You need something that provides the "gyroscope" that keeps the critter upright. For humans, that's a combination of...

  • Our inner ears (air pressure),

  • Sight (visual alignment with surroundings),

  • Touch (heat and air motion),

and a host of other systems all "detecting" how "upright" we are (based on the brain's "I want to do this" control). The result is muscle changes that put us in the position we want (e.g., "upright").

So, first and foremost you need to think abut how your target insect would evolve those basic systems (don't worry to much about the details, you're looking for "good enough" so readers can suspend their disbelief... not so PhD's can nod their heads in agreement that you correctly predicted a million years of evolution).

Goal: how would the insect create it's internal "gyroscope?" If it still has its exoskeleton, then it will need to compensate for the loss of touch (but, for example, it may compensate by developing the ability to detect minute stress against joint muscles).

Delicate Muscle Control

Without electronic help, we really can't detect the bazillion of muscule corrections that occur moment-by-moment to keep us in the position we want (well, when you're standing on your toes trying to screw in a lightbulb with the tips of your fingers you can tell...). However, those adjustments are needed. The basic problem with insects is that most of those limbs have very little in the way of muscles (or whatever squishy goo they use to create basic contractions). They may evolve muscles/squishy-goo such that they can, but that means...

Swiveling Joints

Here's the next problem. Balance requires the bendy parts to adjust in a lot of different directions. If you think about it, your toes, ankles, knees, hips, spine, and shoulders must all make minute adjustments to keep you upright. Nearly everything on those darn bugs is ramrod ridged. Now, exoskeletons means no internal bones. That's OK (...ish) if we evolve really tough "skin" that can better articulate the joints and allow for greater range (and more subtle range) of movement.

Perhaps your biggest challenge here will be side-to-side corrections. Imagine (probably because I saw the picture in another post) a grasshopper standing up. The ability of its legs to "rotate" forward (and, with evolution, backward) covers half the problem, but the basic design means very limited side-to-side correction. If you pushed on his "shoulder," he might just fall over because he can't do anything about it. Without an internal bone structure for hips, our friend might need a short but tough "tube" that extends from the abdomen to the leg, giving it a bit more separation from the body and therefore greater side-to-side range of motion.

The "Other Side" Muscles

Another thing your bugs will need is muscles on the "other side" of the "bone." Humans have muscles, for example, on the front and back of the leg. Those muscles work together to keep you upright. They also allow you to move both backwards and frontwards.

Insects can kinda do this (beetles and spiders better than most, grasshoppers would suck at it) because the legs tend to be engineered for just one or two motions. However, if we think of the "squishy goo" as hydraulics, then everything you need is basically already there: you just need a better pumping system that can precisely forward and reverse the fluid, so to speak.

Goals: joints and "muscles" (aka, hydraulics, I kinda like that idea).

Give your insect these abilities and, while the cute critter won't be the best dancer in the world, he/she would be capable of bipedal locomotion.

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By going the other way conceptually and then back again in the detail work, so take an existing biped like a human, why and how would you put extra arms and wings on a human? The actual anatomical design is going to be fairly similar it's just the surface details that say "bug" or "mammal" or "bird" for that matter.

As to some notes on an actual design; for my money you want not four arms but two pairs of arms, a fine pair for detail work and a heavy pair for brute force projects. I would go with multiple pairs of wings arranged down the back of the torso also, think dragonfly rather than angel. A tail may or may not be useful for balancing large weights etc... that's an argument that can go both ways when you're talking about technological species versus evolutionary necessity.

Now there may be an issue with size, true insects have no lungs; they have something more akin to gills that use air instead of water as a working fluid. They are therefore very strictly limited in their maximum size by oxygen levels, modern insects max out at either 71 or 115 grams, depending on the definitions being used.

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To start, there are few insects that don't have that long abdomen, and that's really what receives support on something like a mantis. I assume we want to keep this feature, as it really is the visual indicator of "insect". If we want that to be supported by two legs, they have to be bulky like on a cricket, but probably not made for jumping, as they'd need to be long, too.

Walking upright with that configuration seems to me as if it would require the mantis' thin upper body, as well. I have a little bit of an issue wrapping my head around the idea of specialized "arms" that double as "legs", though. It doesn't seem like the kind of thing that could happen. It really depends on the kind of arms/hands you want these creatures to have.

I think instead of running on all legs at a greater speed, I would suggest having the back legs be extremely good for running, and joint them in such a way that the insectoid can lean forward for maximum aerodynamics while running. The upper arms, in that case could be used to counterbalance the otherwise lightweight top.

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Your species sort of reminded me of the Mantid from the Warcraft universe. They are an insect race that have 4+ limbs and they are bipedal. They can fly and their bodies can support them walking up right.

If the no-fly thing is important, you can talk about how their wings atrophied as their intelligence or civilization advanced.

The wiki page is limited so you can just google for more information and also search for videos from the related Mantid dungeons on youtube to see how their animations work to get some ideas.

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  • $\begingroup$ Insecta do not have 4+ legs; they have exactly 6 appendages as a defining characteristic. $\endgroup$ – AliceD Oct 10 '17 at 21:13
  • $\begingroup$ God forbid in a fantasy world such as Warcraft, the Earth-specific insect anatomy is not followed realistically. The OP is already talking about intelligent insects walking upright. A possible solution to explain the 2 missing appendages would be due to atrophy during their evolution - like the human tail! $\endgroup$ – Xander Oct 11 '17 at 6:10
  • $\begingroup$ Insects evolved from centipede-like critters as far as I know. So they lost many pairs of limbs over time. The defining characteristic of the Class of Insecta within the order of Arthropods is that the loss of limbs stopped at six, for reasons outlined elsewhere here. Loss of more limbs would make it another class than insects. $\endgroup$ – AliceD Oct 11 '17 at 6:54

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