Special Collection: Insect Biomechanics

This special collection of articles from the Journal of Insect Science brings together some recent papers that focus on insect biomechanics. Biomechanics is an interdisciplinary field with a long and highly influential history, attracting researchers from the fields of physics, engineering, and material sciences. It has served as a major inspiration for the development of new technologies (including robots), and it has provided insights into questions of physiology, neuroscience, and ecology. Mechanics is fundamental to understanding how biological systems work since all living things are structures, acted on by forces, or applying forces to their surroundings to generate movements.

Although biomechanics research is dominated by human (and other vertebrate) studies, insects make particularly attractive model systems for this sort of work for the following reasons:

a) Insects are relatively easy and cheap to collect or to maintain in the laboratory (they are robust, quick to reproduce, and subject to few regulations). 

b) The equipment required to make measurements from insects is generally small and inexpensive (although frequently requires custom design and fabrication). 

c) Insects are remarkably diverse and specialized morphological adaptations can be found for almost any environment. 

d) Because insects are small, complex tissue functions (including neural processing) are frequently achieved using a relatively small number of cells. 

e) Insects have an extremely rich behavioral repertoire with impressive sensory and motor capabilities that are enviable from an engineering perspective.

Ever since the start of modern entomology, there has been a strong interest in the mechanisms of insect movements and the neural processes that control them. This is exemplified by the surgical experiments on Lepidopteran larvae in the early 1900s that attempted to explain how caterpillars coordinate crawling [1-3]. Later on, as new electronic equipment and high-speed film became available, it was possible to study rapid movements such as insect flight [4] or jumping fleas [5] and locusts [6]. This work continues today, making use of digital cameras, pulsed lasers, and semiconductor force sensors to record and analyze the extraordinary acrobatic performance of fast-moving insects [7].

In the last two decades, similar techniques have been employed to study terrestrial locomotion and the kinematics and dynamics of running cockroaches have been described in exquisite detail [8]. This work is particularly important because it has led to the realization that a simple mechanical model (the spring-loaded inverted pendulum, SLIP) is a reasonable description of legged locomotion, from one-legged hopping, through bipedal walking and running, to the scurrying gait of hexapods [9].

From Biology to Engineering. It is widely accepted that insect biomechanics is a mature and fruitful field of study with strong and reciprocal ties to engineering. The impressive motor performance of insects has inspired numerous attempts to emulate their movements using mechanical systems [10]. In engineering, this approach has been called bioinspiration or biomimetics. The motivation behind this method is that solutions to real-world engineering problems have been fail-tested by millions of years of evolution. Although individual mechanisms might not be optimal solutions (natural selection does not act on a single system), they are often very robust and efficient mechanical designs. Of course, this concept extends beyond biomechanics and is useful in the study of sensory systems, neural processing, and materials development.

The outcomes of this approach are too numerous to list but recent insect-inspired devices include robotic caterpillars [11], flapping micro-flyers [12], robots that jump [13], and hexapod machines that can run over complex terrain [14]. Some of the most successful bipedal humanoid and quadruped robots were built using the SLIP model of locomotion as a template for the mechanical structure and movement control systems [15].

From Engineering to Biology. Inspiration can also be drawn in the opposite direction. From a biologist's perspective, these engineered systems can sometimes be used to understand the constraints imposed on a biological system, or to carry out experiments that cannot be done on living animals. This is similar to formulating a mathematical model but using a physical device. One advantage of building a tangible model is that it can be used in a real-world context rather than relying on an approximate physics engine simulation.

Remarkably, this approach has been used to study insect locomotion and behavior for almost 70 years. Relatively few researchers are aware that in the early 1950s Kenneth Roeder built an electromechanical cockroach (“Blatta electromagnetica”) to test some of his theories of photo-taxis and adaptive behavior (related in [16]). A more recent example is the “Robofly,” a scaled insect wing that was used to estimate induced forces during insect flight [17]. Studies on this physical model helped us advance from the perplexed conclusions of classical aerodynamics that “bees cannot fly,” to a detailed understanding of vortex shedding and the effects of viscous drag at low Reynolds numbers.

Efforts are now underway to use these mechanical principles to build micro flying machines that were unthinkable a decade ago [12]. Another example from terrestrial locomotion is the small robot “DynaRoACH,” which was developed to explore the “robophysics” of running on granular media and has provided insights into the challenges faced by small animals trying to move quickly on sand [18].

The Engineering of Biology. This intersection of engineering and biomechanics is now creating entirely new fields of insect research. Some are aimed at understanding the remarkable sensory systems that allow insects to move and navigate so effectively. Others exploit the highly accessible nervous system to study the neural basis of sensory-motor integration. Insects make particularly good model systems because they appear to process sensory information quickly, using fewer components than a comparable vertebrate nervous system.

Some of the more adventurous research in this area is the development of “cyborg” flying insects. Engineers have constructed sophisticated electronic backpacks for large beetles and cockroaches that interface with their sensory or motor systems. Wireless signals are then used to directly drive flight muscles, or to stimulate sensory nerves, so that the insect can be steered during its normal flight [19-20].

The motivation behind these controversial technologies is to avoid “reinventing” entire sensory and motor systems for robotic applications and instead try to exploit existing biological systems. This research could also lead to a better understanding of the basic biology of insect neuromechanics.

Finally, research biologists are interested in using insect muscles as the starting point to grow biological machines that will eventually be living robots [21-22]. Insect tissues have major advantages for this sort of technology and it is hoped that these robots will be recyclable and powered by environmentally sustainable fuels such as sugars and fat. These devices are still a long way in the future, but this research is helping to understand how insect tissues develop and interact to produce some of the most successful and charismatic organisms on the planet.

Barry Trimmer, Ph.D.
Biology Department
Tufts University, Medford, MA. USA

Locomotion

Caterpillar climbing: robust, tension-based omni-directional locomotion
Samuel C. Vaughan, Huai-ti Lin, and Barry A. Trimmer

Honey bees Prefer to Steer on a Smooth Wall With Tetrapod Gaits
Jieliang Zhao, Fei Zhu, and Shaoze Yan

Individual Thigmotactic Preference Affects the Fleeing Behavior of the American Cockroach (Blattodea: Blattidae)
Michel-Olivier Laurent Salazar, Isaac Planas-Sitjà, Grégory Sempo, and Jean-Louis Deneubourg

Drag Reduction in a Natural High-Frequency Swinging Micro-Articulation: Mouthparts of the Honey Bee
Guanya Shi, Jianing Wu, and Shaoze Yan

Orientation

Orientation Inside Linear Nests by Male and Female Osmia bicornis (Megachilidae)
Justyna Kierat, Hajnalka Szentgyörgyi, and Michal Woyciechowski

Wing Kinematics in a Hovering Dronefly Minimize Power Expenditure
J. H. Wu, M. Sun

Body Part Movements

Switchable Wettability of the Honeybee's Tongue Surface Regulated by Erectable Glossal Hairs
Ji Chen, Jianing Wu, and Shaoze Yan

Critical Structure for Telescopic Movement of Honey bee (Insecta: Apidae) Abdomen: Folded Intersegmental Membrane
Jieliang Zhao, Shaoze Yan, and Jianing Wu

Movement Analysis of Flexion and Extension of Honeybee Abdomen Based on an Adaptive Segmented Structure
Jieliang Zhao, Jianing Wu, and Shaoze Yan

Other

Identification of Nanopillars on the Cuticle of the Aquatic Larvae of the Drone Fly (Diptera: Syrphidae)
Matthew J. Hayes, Timothy P. Levine, and Roger H. Wilson

Measuring the strength of the horned passalus beetle, Odontotaenius disjunctus: Revisiting an old topic with modern technology
Andrew K. Davis, Barrett Attarha, Taylor J. Piefke

The Only Blue Mimeresia (Lepidoptera: Lycaenidae: Lipteninae) Uses a Color-Generating Mechanism Widely Applied by Butterflies
Zsolt Bálint, Szabolcs Sáfián, Adrian Hoskins, et al.

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