Month: May 2013

Insect Bits & Bytes (May 2013)
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Insect Bits & Bytes (May 2013)

This month’s topics:

Compound eye-inspired camera

Robotic Flyer

Water-repellent, self-cleaning cicada wings

Thin film interface inspired by moth eyes

Ants tunneling, falling and catching themselves

Sound perception in moths

Jumping Robots

Some of you might be thinking that the topic of this blog is rather narrow: “How can she possibly sustain this blog because she is going to run out of topics at some point…soon”.

Or is that just the voice in my own head talking?

I only have to remind myself that I have chosen a taxon, the Insecta, which is extremely diverse and that new species are being discovered and described every day, so it is very likely that I am going to be occupied for a while. Insects have adapted to many different environments, often through very novel and varied (compared to mammals) adaptations. Inspiration for innovation is bound to be found in common insects, but also in the obscure. And if I adopt the often ignored non-insect arthropods such as ticks, mites, spiders, etc., then I will be set until retirement. At the same time imaging and manufacturing techniques are making the small visible and producible so advances in engineering are helping me stay off the streets too.

In this inaugural “Insect Bits & Bytes” post I highlight some of the research I came across on Twitter (#biomimicry or #bioinspiration) during the month of May. These studies all involve new technologies that were inspired by insects or basic discoveries about insect biology that could lead to new innovations.

I have compiled a list of links to this work, as well as to coverage of the research by some of my favorite science writers. I hope to do the same at the end of every month.

Compound eye-inspired camera

The biggest insect-inspired technology story came from the University of Illinois at Urbana-Champaign (my home institution). John Roger’s material science lab was inspired by the insect eye to develop a new digital camera.

RogersBeeEye

New digital cameras exploit large arrays of tiny focusing lenses and miniaturized detectors in hemispherical layouts, just like eyes found in arthropods. Photo credit: John A. Rogers, UIUC

These hemispherical cameras depend on the manufacturing technique that has been perfected in the Roger’s lab – manufacturing flexible electronics.

Engineers have tried to manufacture compound eyes before. In 2006 UC Berkeley’s Luke Lee fabricated an artificial compound eye in his lab. He created thousands of closely packed light-guiding channels leading to pin-head-sized polymer resin domes and then topping each dome with its own lens. Each individual unit is very similar to an insect’s ommatidium (the individual unit of the compound eye). The fabrication method itself was based on the developmental stages of the insect, and resulted in a 3D artificial compound eye that is similar in size, shape and structure to the insect’s compound eye.

In my opinion, because of how the “eye” is manufactured and functions, Lee’s artificial eye is closer to its model than this new bioinspired eye from the Roger’s lab. Time will tell if, by adding engineering shortcuts in manufacturing, and by using materials that work better with how we currently use electronics, a more useful camera or sensor is created.

Reference: Song, Xie, Malyarchuk, Xiao, Jung, Choi, Liu, Park, Lu, Kim, Crozier, Huang & Rogers. 2013. Digital cameras with designs inspired by the arthropod eye. Nature http://dx.doi.org/10.1038/nature12083

Coverage:

Robotic Flyer

Over the years it has been exciting to see how small engineers can make flying robots. Research by people like Michael Dickinson on insect aerodynamics have helped engineers such as Ron Fearing and Rob Wood to develop microrobots that can fly. This past month we learned that the Wood lab at Harvard’s Wyss Institute has now manufactured a controllable robot, the size of an insect, that can fly. (Note: the manufacturing process for these types of robots is really cool too.)

One of the major remaining challenges, before microrobots will be used on a grand scale, is to get them enough power to walk, run, swim and/or fly for an extended time (note the tether in all the flying minirobot pictures and videos). There is just not enough room on a small robot to incorporate conventional batteries, or even smaller lightweight battery sources like a coins cell or solar panels. Future advances may involve biological motors as power sources. Maybe we can even learn more about basic insect flight energetics (a very interesting topic) and incorporate what we learn about basic insect physiology into microrobots.

Reference: Ma, K. Y., Chirarattananon, P., Fuller, S. B. & Wood, R. J. 2013. Controlled flight of a biologically inspired, insect-scale robot. Science. http://dx.doi.org/10.1126/science.1231806

Coverage:

Water-repellent, self-cleaning cicada wings

Cicadas all over the news these days. The East Coast of the US is in the midst of the 17-year periodical cicada emergence. This year cicadas are apparently also of great interest to those studying biological materials at the nanoscale. Earlier this year it was reported that nanopillars on clanger cicada wings can tear bacterial membranes apart. One can think of interesting applications for engineered materials that incorporate similar structures.

This month another study showed that cicada wings are also extremely hydrophobic; droplets pretty much jump off of the surface. The wings are thus self-cleaning. Again, one can think of multiple applications for an engineered hydrophobic material based on the cicada wing. Then again, there are many other examples of biological materials that have similar characteristics: lotus leaf, Namib beetle, etc. One interesting idea that Charles Choi brought up in his article (link below) is the use of cicada-wing technology in power plants. Jumping droplets would help dissipate heat.

Reference: Wisdom, K. M., J. A. Watson, X. Qu, F. Liu, G. S. Watson & C-H. Chen. 2013. Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate. Proceedings of the National Academy of Sciences of the USA. http://dx.doi.org/10.1073/pnas.1210770110

Coverage:

The coverage of this story was, and still is, plagued by a #TaxonomyFail (pointed out to me by @BrianTCutting). Most of the coverage associated with this story showed a picture of a wet fly, sometimes a wet fly that was upside down. Soon I hope to add a picture to this post of a wet Brood II cicada. Stay tuned.

Thin film interface inspired by moth eyes

The insect eyes have it, again.

Moth eyes were the inspiration for a new multilayered material which may find application in optoelectronic devices such as solar cells. For at least 40 years we have known how nature solves the problem of light reflection. We only now have the imaging and manufacturing capabilities that will enable us to engineer and produce materials that mimic the most effective nanostructures.

Moths are generally nocturnal and any light the eye can “harvest” is a plus, reflection of light needs to be minimized.

motheye

Moth eyes reflect very little incident light. (Image by Daniel Meyer)

The “moth eye” principle was first described in 1973 by Clapham and Hutley. Their electronmicrographs showed that the surface of corneal lenses of moths are covered with conical nanostructures and it was proposed that these structures suppressed interference (reflection).

Over the past decade nanostructured materials mimicking the moth eye have been manufactured through techniques such as ion-beam etching, but application was limited because the material could only be manufactured at a small scale. Recently researchers at North Carolina State University were able to manufacture interfacial nanostructures protruding from a silicon layer into a overlaying thin film and thus eliminated interference effects. It remains to be seen if the manufacturing technique proposed in this recent work can be scaled up to produce consistent nanostructures at a reasonable cost.

Reference: Yang, Q., X. A. Zhang, A. Bagal, W. Guo & C-H Chang. 2013. Antireflection effects at nanostructured material interfaces and the suppression of thin-film interference. Nanotechnology http://dx.doi.org/10.1088/0957-4484/24/23/235202

Coverage:

Ants tunneling, falling and catching themselves

Physicists and biologists worked together to explain how fire ants tunnel through the ground. The types of descriptions of locomotion will help engineers build more useful robots.

Obviously legs are important for locomotion on land, however, functional feet may not be just the distal end of a leg (cockroach). Also, appendages such as tails, are essential for dynamically stable locomotion (gecko). These types of biomechanical principles have already been incorporated into robots. Now a recent study from Georgia Tech shows that additional appendages, antennae, do not just serve as chemical or mechanical sensors. When falling the antennae help the ant grab onto the tunnel wall. Civil engineers might also learn from this biological example since ants build tunnels close in diameter to their own body length, no matter what the substrate, so that all legs and antennae can help get a grip when falling.

Reference: Gravish, N., D. Monaenkova, M. A. D. Goodisman & D. I. Goldman. 2013. Climbing, falling and jamming during ant locomotion in confined environments. Proceedings of the National Academy of Sciences. http://dx.doi.org/10.1073/pnas.1302428110

Coverage:

Sound perception in moths

Turns out that the animal with the best hearing is the greater wax moth (one of the many scourges of bee keepers). Moths have a tympanum on either side of the abdomen. Each tympanum is innervated by just two sensory receptors. These receptors start firing at the slightest displacement of the “ear drum”.  Turns out that the greater wax moth can sense displacement caused by frequencies up to 300 kHz. In addition, this type of auditory system works at a wide range: from 20 kHz up to 300 kHz.  Engineers are keen on building a mechanoreceptor as sensitive to ultrasound as this, and with materials and structure as “basic” as a moth’s ear.

Interestingly ultrasonic sensors are preferred over photoelectric sensors in certain situations – now bioinspired technologies based on the moth eye (see above) and the moth ear may blur those distinctions.

Reference: Moir, H. M., Jackson, J. C. & Windmill, J. F. C. (2013) Biology Letters. http://dx.doi.org/10.1098/rsbl.2013.0241

Coverage:

An illustration from British Entomology by John Curtis. Lepidoptera: Galleria mellonella

An illustration from British Entomology by John Curtis. Lepidoptera: Galleria mellonella

Jumping Robots

Also, everyone’s favorite feisty insect-inspired robot, Rhex, learned to jump.

Reference: Johnson, A. M. & D. E. Koditschek. 2013. Toward a vocabulary of legged leaping. Proceedings of the 2013 IEEE Intl. Conference on Robotics and Automation. http://kodlab.seas.upenn.edu/Aaron/ICRA2013

Coverage:

Miscellaneous

Not sure if this is biomimicry or bioinspiration, but it involves insects and it is cool:

It was a insect-spirational month! Let me know if I missed anything.

I wonder what June will bring.

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The Dawn of the Artificial Coprophages
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The Dawn of the Artificial Coprophages

A history of insect-inspired walking robots and how they “evolved”.

Earlier this year our Department of Entomology at the University of Illinois at Urbana-Champaign hosted the 3oth Annual Insect Fear Film Festival. This year’s theme was InsX-files and combined two “alternative” communities – those passionate about insects and those passionate about a TV show that has not been on the air for years, the X-files. You might be surprised to learn that even in the Midwest these communities can fill up a big lecture hall no problem (I was).

xfiles1

30th Insect Fear Film Festival Promotional Design (Theme: Ins-X Files). Designed by Joseph Wong for Illinois’ EGSA.

Special guests at the festival were series creator, writer, producer and director Chris Carter and the writer of some of the most popular episodes of the show Darin Morgan. (For scenes from the festival check out the tweets at the end of this post)

One of those episodes, entitled: “War of the Coprophages” (1996), was shown at the festival. This particular episode has achieved cult status here at Illinois because it features the character Bambi Berenbaum, who in her appearance and mannerisms is exactly like nothing like our fierce leader and Department Head May Berenbaum. (Morgan consulted various books authored by May and thus decided to give the fictional USDA scientist a name that honored her).

Another reason why I love this episode (besides the fact that it is basically a fantastic piece of suspenseful science fiction writing) is that it featured insect-inspired robots. In short, a town somewhere gets overrun with cockroaches that may be killing people. Some of the roaches appear to be mechanical rather than biological. Agent Mulder decides to visit a researcher named Ivanov at the Massachusetts Institute of Robotics to get a better idea about what engineers are up to.

SCENE 14: MASSACHUSETTS INSTITUTE OF ROBOTICS

(Mulder walks down the stairs and then a hallway. A small, insect-shaped robot walks down the adjacent hallway (and manages to erase the title of the location as he does somehow.) Mulder watches as it walks into a room, then comes out and looks at him. As Mulder takes a few steps towards him, the insect back away. Mulder follows the insect to a laboratory where the insect robot disappears. Mulder hears a similar whirring and turns around to see Doctor Ivanov approaching him on his wheelchair. The scientist talks out of a microphone that is near his throat. A laptop computer is hooked onto the wheelchair.)

IVANOV:For decades, my colleagues in artificial intelligence have attempted to create an autonomous robot. By struggling to give their machines a human-like brain, they have failed. A human brain is too complex, too computational. It thinks too much. But insects merely react. I used insects as my model, not just in design but by giving them the simplest of computer programs. “Go to the object. Go away from the moving object.” Governed only by sensors and reflex responses, they take on the behavior of intelligent, living beings.

MULDER: So this one is just programmed to head towards any object moving within the field of its sensors?

IVANOV: No.

MULDER: Then why is it following me?

IVANOV: He likes you.

MULDER: Your contract is with NASA?

IVANOV: The goal is to transport a fleet of robots to another planet and allow them to navigate the terrain with more intricacy than any space probe has done before. It, it sounds slightly fantastic, but the only obstacle I can foresee is devising a renewable energy source. In any case, this is the future of space exploration. It does not include living entities.

Robot1

Robot2

Screenshots from the X-files episode “War of the Coprophages” showing two of the insect-inspired robots featured in the episode.

Genghis

Darin Morgan could have gleaned inspiration from another University of Illinois Entomology Faculty member for ideas about robots, namely Fred Delcomyn who around 1996 was also working on a cockroach-inspired robot. Instead the Ivanov character is clearly based on MIT’s Rodney Brooks, a roboticist who, at the time, wanted to move away from incorporating Artificial Intelligence into robots and instead conceived of robots that were more adaptive to their environment. By programming only simple modules of behavior into the robot, rather than complex reasoning parameters, and let the robot thus react to the environment, Brooks felt that he could build some very functional robots. Much like the ones featured in the X-files episode.  Brooks’ mid-nineties robot is named Genghis (~1991). Genghis was the first robot created by the iRobot Corporation (now of Roomba fame) and was intended for possible planetary exploration.  Other insect-inspired robots from Brook’s MIT “Insect Lab” includes Boadicea which employs a differential leg design to allow for longer stride frequencies and an increase in speed (the cockroach Blaberus discoidalis served as the model). Both Genghis and Boadicea are robust to failures in leg function, much like animals that can adopt a compensatory gait. Choosing robustness over perfection is a characteristic that shows up again and again in successful bioinspired robot design.

Genghis

A hexapodal robot named Genghis from the Brook’s lab at MIT (designed around ’91). The robot was also relatively cheap thanks to innovative construction methods. Genghis used 4 microprocessors, 22 sensors, and 12 servo motors. (Picture from NASA.gov)

Around the same time that Genghis became famous other research groups in the United States also started building walking robots that incorporated the biomechanics of actual terrestrially locomoting insects.  I review some of the more successful projects here.

Why build robots based on insects?

  • Insects exhibit behaviors that are considered relatively simple, and thus easier to emulate. The resulting behavi0r may appear complex or purposeful to the observer but it is actually derived from fairly simple rules on how the nervous system perceives environmental inputs and how an internal “neural” pattern generator relays this information to “external” mechanical components (muscle, legs). Of course, “simple” is relative. Different situations may also result in different behaviors (and neural input). For instance, when cockroaches are close to wall they tend to amble, at this speed the animal is very sensitive to nervous feedback from its surroundings, each individual leg is more sensitive to this feedback. When roaches trot really fast across open spaces then a central pattern generator may “suffice”. This CPG generates rhythmic movements in a neural circuit, with little feedback from the environment.
  • In addition, the exoskeleton and the muscles stabilize insects without the involvement of the nervous system. Hexapod locomotion is dynamically very stable (this claim was conclusively proven by adding jet-packs to roaches…oh, yes, indeedy). Just like its model insect-inspired robots basically uses 2 tripods for locomotion; at any time during the gait the insect has three feet on the ground. The sprawled posture also results in passive stabilization of lateral motion, it is very difficult to push over an insect or a robot using 6 legs. (For a very detailed explanation of these two points please watch this March 2013 seminar by Princeton’s Philip Holmes)

Cockroach tripod 2013-05-23 (10.33.59-438 PM)

Phase Diagram 2013-05-23 (10.33.59-186 PM)

Top figure: Cockroaches walk with a tripod gait: they always keep one tripod of legs (the foreleg and hindleg from one side and the middle leg from the other) in contact with the ground, alternating the tripods as they walk.  In the bottom figure are respresented the stance phases of the two different tripods (red or blue) (Drawings by Marianne Alleyne)

  • Another goal of roboticists has always been to miniaturize their creation. Making cheap little robots is still the goal. Smaller robots can potentially survey areas that are currently not accessible. Also, if you have multiple smaller robots available then you can send more to one area, each carrying cameras and chemical sensors, while a robustness (missing or non-functioning individual robots) is built into the system. As we shall see, miniaturizing brings its own challenges. Insects are small, some insects live in social groups, so there is lots to learn about miniaturization and swarming from them.
  • It is also much easier to make a robot that has an exoskeleton that is segmented (rather than an animatron that has an endoskeleton). Insects are segmented animals and in some of the insect-inspired robots we see this segmentation too because it increases flexibility.

Since the 1996 episode of the X-files many other insect-inspired walking robots have spawned. Even evolved.

1. RHex – Robotic Hexapod.

Insects such as cockroaches served as the biological inspirations for RHex. Data on bio-mechanics and dynamics of insects maneuvering over rough terrain were obtained by the researchers from the PolyPedal lab at UC Berkeley (Robert J. Full is the primary investigator of the lab) (For full disclosure the author of this blog was once an undergraduate in the PolyPedal lab working on the energetics of locomotion in crustaceans). (Bob also gave 3 very informative TED talks)

Terrestrial animals (bipeds, quadrupeds, hexapeds, octopeds) all rely on a spring-mass system where the limbs (incl. muscle and cuticle) have a spring-like function to help support the animal’s weight over the course of the stride (larger animals have stiffer springs). In addition, the neural control of muscle action during walking and running is linked to muscle stiffness and thus the spring.

The biological data was then used by engineers Dan Koditschek (at the University of Pennsylvania), Al Rizzi (Carnegie Mellon University) and Martin Buehler (then at Boston Dynamics) to build a robust autonomous robot that was able to transverse uneven ground without actual terrain sensing or actively trying to control adaptive maneuvers.

Despite the fact that RHex legs have many degrees of freedom (many legs, joints and actuators), by incorporating real biological data and following the simple rules of a spring-mass system a robot was created that is quick (as measured in body lengths per second), maneuverable, and robust.

One of the most striking advancements of RHex was the compliant legs which were made of materials that helped with dynamic stability, shock absorption, energy efficiency, enhanced gait control, obstacle avoidance, etc. (RHex is now part of the Boston Dynamics robot-thoroughbred stables)

RHex

One generalized version of RHex (Robotic Hexapod), the first legged robot to run over uneven terrain, and the first autonomous legged platform to run at speeds above one body length per second. (Drawing by Marianne Alleyne)

Since funding for RHex started in 1998 RHex has evolved into different versions (species?). By 2012 feisty RHex had developed into this:

And very recently it was announced that RHex is also able to leap.

There is also a a cost-efficient education and research version called EduBot.

(For some great pictures and video of RHex click on this Boston Dynamics website).

For an explanation on how you can use biological research (by Joe Spagna and others) done with RHex in your college courses and outreach project click here.

2. Sprawl

Whereas I have always found RHex to have a spunky personality the robot Sprawl to me seemed to have something sinister about it. Must be because of all the wires and (pink!) tubing. Of course, some of the more “evolved” versions have names such as Franken-Sprawl or Sprawlita which does not help them win cuddliest-robot contests.

Member of the Sprawl family. One of the first fully dynamic locomoting hexapods. (Drawing by Marianne Alleyne)

Member of the Sprawl family. One of the first fully dynamic locomoting hexapods. (Drawing by Marianne Alleyne)

The Sprawl family of robots were created by Mark Cutkosky‘s group at Standford University’s Center for Design Research, again using data from Berkeley’s Polypedal lab. The Sprawl robot incorporates biological principles not only in its leg arrangement and design, but also in its construction and in the material properties of its structure. The robot was made using (then) modern manufacturing techniques (shape deposition manufacturing) to create limbs of the right shape and with the desired material properties, like stiffness at certain critical points. Early Sprawl robots used pneumatic actuators, whereas the later iSprawl robots used electric motors and flexible cable drives. The final result is a sturdy and super-fast robot that resembles a scurrying cockroach. Over the years Sprawl (now called Sprawlettes) have become smaller and smaller (currently you can hold one in the palm of your hand) and they can now be batch-manufactured.

3. Whegs

Another successful collaboration between biologists and robotocists can be found at Case Western Reserve University. Since the 1990s Mechanical Engineer Roger Quinn’s group has used data from neuroscientists such as Roy Ritzman to build cockroach-inspired robots that can walk and climb (for instance, the hexapod Robot III from ~1999). One line of robots is the WHEGs family of robots which use a Wheel-Leg hybrid. The robot was inspired by the European Space Agency’s Prolero robot and RHex, but instead of using 6 motors to drive individual legs (as RHex has) it only uses one powerful one, which can distribute its power to all or just a few of the legs.

Whegs...(Drawing by Marianne Alleyne)

Representation of an early model Whegs: this robot comines the advantages of wheels (speed) and legs (maneuver over obstacles) (Drawing by Marianne Alleyne)

The later models of Whegs mimic cockroach maneuverability to manage uneven surfaces. In addition, cockroach behavior during locomotion is copied by adding a variety of sensors. Cockroach rely on antennae to guide them over and under obstacles.  Whegs robots are fitted with mechanical antennae that mimic the movements of the cockroach antennae and to help the robot “make decisions” about the best way forward.

The future is here

All the robot research groups that have been working on insect-inspired robots such as Genghis, RHex, Sprawl and Whegs, and the students that came out of these laboratories to start their own groups, have branched out into other areas of research (some of which involve insects). The focus may have shifted to:

The biggest challenge to robotics is powering small insect-sized robots. We can still learn a lot from insect’s operational duration. Making a robot work for 5 min is great. However, insects work for days on end. We need to incorporate similar power management strategies and power budgets into our robots. This becomes even more critical as we scale down in size because available power doesn’t scale linearly with length. Less power can be stored per unit volume as you get smaller because the power/packaging ratio goes down. The miniaturization and power issue is especially critical for developing smaller flying robots. (Insect flight will be covered in a later blog post)

One area where we can also still learn from insects, and which in my mind has been somewhat ignored, is the fact that insects can recycle large parts of their exoskeleton...maybe this can become a focus too. I will explain more about the beauty of the materials that make up the insects exoskeleton in one of my next few blog posts.

Until then, all you need to remember about this post is that “The truth is out there”.

#IFFF30 Recap:

I did not do it first.
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I did not do it first.

To some of my entomology friends the title of this blog may not seem particularly original.  That is probably because they are familiar with the book “Insects Did It First” by Roger D. Akre, Gregory S. Paulson and E. Paul Catts (1992). I had my heart set on this blog title (with the subtitle “Can Engineers Do It Better?”) before I was aware of the book.

My used-copy of the book of the same name as this blog. (Picture by Marianne Alleyne)

My copy of the book with the same name as this blog. (Picture by Marianne Alleyne)

All three authors were entomologists and associated with Washington State University (Dr. Paulson now teaches at Schippenburg University of Pennsylvania). The book “Insects Did It First” is a collection of ideas, started in 1964 by Akre, that linked an “advanced” human technology to insects. The book is a perfect example of how to get the general public to become more interested in the natural history of insects. The book is even more endearing because of the wonderful, often humorous, drawings by Catts.

1stdome

Typically whimsical drawing by E. Paul Catts from “Insects Did It First”. – picture featured on Gregory Paulson’s website (click drawing).

All 81 short “chapters” of the book cover an achievement in which insects were far ahead of humans. Some examples are obvious and famous (e.g. insects as builders of energy efficient structures), other are less well known to non-entomologists (e.g. preserving and storing food without freezing).

In some ways this blog is similar to the Akre, Paulson and Catts book – but using a media that may be more accessible to more people. Just like the author-trio my ultimate goal is to promote insects as inspirational to those outside of entomology. I hope to especially reach engineers, designers and entrepreneurs. I may cover some of the same topics, but since the book was last published in 1992 (Dr. Akre passed away in 1994 and Dr. Catts in 1996) I will be able to give more updated information. The blog will also be different in that I want to go beyond natural history and delve a little bit deeper into the topics of technology and innovation. In addition, there are characteristics of insects bodies, their behaviors, the ecosystems they live in, etc. that I think have not yet been considered in depth by engineers. I will promote those topics too. For instance, the Akre book does not cover the springing mechanism of Collembola which I covered in my previous post (maybe because Collembola are not insects?).

Ultimately I hope that my blog will be thought of as fondly as the Akre book.

See Dr. Paulson’s website for some sample chapters and drawings.

And then get your copy of the book at Amazon. The book is out of print now but there are still some used copies available.

(Stay tuned for next week’s blog post (also on a topic not covered by the Akre book) on how insect-inspired robots evolved between famous X-files episode and now.)

Jump! Go Ahead, Jump, Little Springtail.
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Jump! Go Ahead, Jump, Little Springtail.

And here it is. Behold the best blog-banner ever – created by Nils Cordes*! 

Of course, the premiere of such a great banner also requires a blog post that explains it. So let me try.

The animal featured in this blog’s banner is a springtail from the hexapod lineage Collembola. Collembola are not insects but entomologists are an inclusive bunch so we gladly incorporate spiders and entognathous creatures into our studies and teachings.

Springtails are very likely the most abundant arthropods on earth. They occur in the soil (different species at different depths), in leaf litter, moss, under logs, etc. One of the most distinguishing features, if you can consider anything on an animal that is only 0.12 to 17 mm long distinguishing, is the forked furca at the posterior end of the animal. The furca is present in a lot of species, but not all. Those that live deeper in the soil usually lack the structure because they do not need it since its main function is for jumping.

CollembolaBoth

Generalized “elongate” (top) and “globular” (bottom) Collembola. Furca (springing mechanism) in red – the springtail at the top has the mechanism partly retracted and the springtail in the bottom picture has the furca extended. (Marianne Alleyne)

Collembola species can have varying body shapes, but generally there are those with elongated bodies and those with more globular bodies. Collembola can walk, run and climb, but the locomotory specialty that they are best known for (and which seems to be rather ancestral) is jumping.

Globular Springtail Dicyrtomina saundersi. Body length = 1.7mm. Picture by Lord V. Used with permission.

Globular springtail Dicyrtomina saundersi. Body length = 1.7mm. Picture by Lord V. (Used with permission.)

Picture by Lord V. Used with permission.

Elongate springtail. Body length = 2.3 mm. Picture by Lord V. (Used with permission.)

This excellent picture by Lord V is of a picture walking over a glass slide. Clearly visible is the forked furca that can prope the springtail into the air.

This excellent picture is of a springtail’s underbelly. The picture was taken by Lord V as a springtail walked over a glass slide. Clearly visible is the forked furca that can propel the animal into the air. (Used with permission.)

Collembola can jump multiple times in a row, those with globular bodies and more advanced tracheal systems more often (1). In general, springtails tire easily so that jumping is usually only used as an escape mechanism. The jump can take the animal in any direction. Since the furca is located at the extremity of the body, directly beneath the center of gravity, the dynamics of the jump cause the body to rotate head over end. Some Collembola species can jump very high, others take a shallower trajectory but land far away from point of takeoff.

This jumping escape response is quite successful but it does require modifications of the entire body plan. The cuticle, the (hydrostatic) endoskeleton, tendons, and muscles all work together to manipulate the body in such a way that the propulsion is optimal.  How exactly this happens is not very well understood, yet this system holds inspirational lessons for passively compliant locomotory structures.

At rest the furca is held within a ventral groove of the abdomen. At the time of the jump the furca moves from this resting (retracted) position to the extended position. Based on morphological and kinematic observations (there is no direct experimental evidence) it appears that as the furca moves it compresses a “spring”. After it passes a critical point of extension the spring releases all the energy, which in turn causes the springing organ to snap out at high speed. If this happens as the springing organ hits a substrate a force is created that propels the animal upward.

The springing mechanism of a generalized springtail; partially retracted (left) and extended (right).

The springing mechanism of a generalized springtail; partially retracted (left) and extended (right). (Marianne Alleyne)

What exactly comprises this “spring” is not clear. Earliest experiments done by Manton (2) in the early 1970s concluded that to evert the springing organ the body’s hydraulics (pressure on the fluid that makes up most of inside of the body = hemocoel) was important. However, later in the 1970s, Christian (3) concluded that direct muscle action, and not necessarily hydraulics, was the main force inducer. In the 1990s, when high-speed photography had advanced greatly, Brackenbury and Hunt (4) concluded from their experiments that hydraulic forces created by pressurizing the hemocoel increases tension on abdominal sclerites (the exoskeletal plates) that results in a click mechanism that propels the animal into the air. All these studies do agree that elastic elements within the base of the springing organ and within the exoskeleton, as well as the body as whole, are important too. To what extent is not known.

Click mechanism model of the furca. The furca, at rest, is retracted into an abdominal ventral groove. A pair of "basal rods" (springs) are embedded in ventral and lateral parts of the abdominal sclerites 4 & 5, these springs also attach to the apex of the furca. The spring/click mechanism gets help from muscle and active dorsiflexion of the body, which both help release to spring organ from the groove)

Click mechanism model of the furca (red) and distal end of abdomen. The furca, at rest, is retracted into an abdominal ventral groove. A pair of “basal rods” (springs, in blue) are embedded in ventral and lateral parts of the abdominal sclerites 4 & 5, these springs also attach to the apex of the furca. The spring/click mechanism gets help from muscle and active dorsiflexion of the body (in orange), to release the spring organ from the groove. After the furca passes a critical point of extension the spring releases all the energy. (Drawing by Marianne Alleyne based on Brackenbury & Hunt, 1993)

Imagine a beam or a chopstick that’s flexible transversally but somewhat stiff longitudinally. If you compress it, it doesn’t change…up to a point. Then it ‘snaps’ out and buckles. You get a rapid displacement as all the strain energy is released. The exoskeleton of the springtail does a similar thing. It stores the strain energy and then goes through a snap-through buckling phenomenon to produce large strain motion which is then amplified by the tail and presto…springtail in motion.

Many insects, and other animals, use musculoskeletal springs that are incorporated into the complete body plan.  These springs help achieve a high rate of acceleration, or a further jumping distance, and help save metabolic energy. Based on these findings compliant structures and materials have been incorporated into bioinspired legged robots (5). Compliant legged robots achieve a few important things: increased energy efficiency, increased speed, ability to avoid obstacles (in case of jumping robots), and the ability to use more simplified controls to enable enhanced gait control and shock absorption. Springs in bioinspired robots have used elements such as airsprings (e.g. compressed air) and compliant materials, but improvement is still possible. Airsprings, for instance, are not very efficient because they end up converting much of the energy they store into heat. In addition, some of the compliant materials are better than others. Rubbery materials, like elastomers, tend to have a fair bit of viscosity in them and so some (maybe lots) of the energy that it stores is lost to heat as well. For high efficiency, most robotic-type systems currently use mechanical springs (i.e. metals). Bioinspired robots also incorporate series elastic actuators that have linear springs intentionally placed in series between the motor and actuator output, which results in the actuator being bulky.

The variety of jumping mechanisms among insects is great (think: click beetle, flea, grasshoppers, treehoppers, etc.). The intriguing aspect of the jumping mechanism in springtails is that it operates so efficiently at a very small scale, much smaller than any bioinspired robot that has been developed. In the future we will be able to manufacture almost microscopic devices incorporating different characteristics into small structures using “springs” and compliant materials.

Maybe we can incorporate locomotory mechanisms that propel the object, using very little energy. Inspiration for what materials to use and how to construct the object can be found through further study of the springtail’s click mechanism. Somewhat surprisingly not much research has been published on this system since the 1990s. Yet with help from today’s high-speed cameras and microscopy techniques we should be better able to understand how the springtail propels itself. Advanced computer aided engineering (CAE) tools, like finite element analysis (FEA), could be used to augment the visual data and elicit some fundamental internal characteristics that are not visibly detectable.

By researching this topic I thought of a few applications for technologies based on the Collembola’s spring mechanisms. Click mechanisms at the scale of a springtail’s springing mechanism could possibly aid stent design or inspire development of other deployable structures that snap open or closed based on certain environmental conditions. Maybe small springing mechanisms can be incorporated in groups and serve as strain sensors on bigger structures. And who wouldn’t welcome millimeter-sized robots that can perform in a futuristic “flea circus”?

PLEASE LEAVE A COMMENT (OR CONTACT ME VIA TWITTER @COTESIA1) IF YOU HAVE ANY NOVEL IDEAS FOR A SPRINGTAIL INSPIRED JUMPING MECHANISM. JUST IMAGINE.

REFERENCES:

(1) B. Ruhfus and D. Zinkler, Investigations on the sources utilized for the energy supply fueling the jump of springtails, Journal of Insect Physiology, Volume 41, Issue 4, April 1995, Pages 297-301, ISSN 0022-1910, 10.1016/0022-1910(94)00122-W.

(2) S. M. Manton. The Arthropoda: Habits, functional morphology, and evolution. Clarendon Press, Oxford, 1977. ISBN: 019857391X

(3) E. Christian. The jump of the springtails. Naturwissenschaften, Volume 65, Issue 9, 1978, Pages 495-496, 10.1007/BF00702849

(4) J. Brackenbury and H. Hunt. Jumping in springtails: mechanism and dynamics. Journal of Zoology, Volume 229, Issue 2, 1993, Pages 217-236, ISSN 1469-7998, 10.1111/j.1469-7998.1993.tb02632.x

(5) Z. Zhou and S. Bi. A survey of bio-inspired compliant legged robot designs. Bioinspiration and Biomimetics,Volume 7, Issue 4, 2012, 20 pages 10.1088/1748-3182/7/4/041001

SPRINGTAIL RESOURCES:

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*My friends can attest to the fact that I have been talking for a long, long time about starting a blog about how we can use insects to inspire new technologies. One of these friends who had to humor me for so long is Nils Cordes. I met Nils when he was a student at Illinois, but he is currently finishing up his PhD at the University of Bielefeld in Germany. Nils is a great scientist, and a great communicator. He is also a wonderful artist. He offered, those many years ago, to create some art work for this (then still imaginary) blog that I was going to use to communicate my love of insects. And he did…behold the best blog banner EVAH!