Biomimetics - Biologically Inspired Technologies - Yoseph Bar Cohen Episode 2 Part 3 ppt

In general, camouflage and armor are inimical; the tendency is for the more primitive ¼ evolutionarily older animals of any particular phylum to be well armored but slow and relatively e

13.10 Riot Control Agent 358

13.10.1 Chemical Mace 358

13.11 Operational 359

13.11.1 Long-Term Disablement 359

13.11.2 Passive Deterrents 359

13.12 Physiological 359

13.12.1 Neurochemical 359

13.12.2 Diversion 360

13.13 Surveillance 360

13.13.1 Electrosensing 360

13.14 Conclusions 361

References 361

Whilst there are several proposed uses of biomimetics in defense or attack (martial, general law enforcement) systems, at present they seem to be mostly development of novel materials (occa-sionally novel mechanisms) in an established context Examples are armor, personal or otherwise, made of analogs of silk, mother-of-pearl (nacre), or wood I do not intend to rehearse this topic further Camouflage is another area that has been examined, especially adaptive camouflage, but since there is still much to be learned about camouflage techniques in nature (which I take to include mimicry — camouflage is ‘deception’), I have included it In general, camouflage and armor are inimical; the tendency is for the more primitive (¼ evolutionarily older) animals of any

particular phylum to be well armored but slow and relatively easily seen, whereas the more highly evolved ones are less well armored, or have no armor at all, but are fast-moving, or very well camouflaged, or both Thus they rely on speed and behavioral adaptiveness and subtlety for their safety The inevitable conclusion is that nature often employs guerrilla techniques rather than what

we think of as ‘‘conventional’’ ones This may be related to the perceived financial investment In human warfare, an infantryman is seen as more expendable than the combination of a pilot and aircraft Indeed a significant reason for having a pilot is as a hostage to the aircraft’s expensive technology, so that it is brought back in one piece from a sortie

The preparation of a chapter like this is especially difficult since I could not think of a suitable narrative to cover all the possibilities that exist in nature Also, I have little understanding of the techniques that are available to, or desired by, the military and police (the obvious users of defense mechanisms) I decided, therefore, to adopt a classificatory approach, and to use an existing military classification as my template (Alexander et al., 1996) I have removed the obviously nonbiological techniques that involve explosives, lasers, etc., have retained others which, although biology does not present us with the same resource, are obvious functional analogs, and have included some that seemed to be missing from Alexander’s list but are present in biology These latter are presented without citations

Man has many martial devices that have their reflections in nature, but the similarities have either not been recognized or have not been developed And since the outcome in nature is, mostly for all parties, in an intraspecific encounter to live to fight another day (or at least live), perhaps we have still much to learn As for the rest, I suspect we have an untapped resource for biomimicry;

I have mostly left the extrapolation from biology to technology to the reader, otherwise this chapter would have been too long But most of the examples quoted either have a technological counterpart

or could be realized without much difficulty

The Department of Defense defines (non-lethal) weapons as designed and deployed so as to incapacitate people or their weapons and other equipment, rather than destroying them; also to

have minimal effects on the environment Unlike conventional, lethal, weapons that destroy theirtargets principally through blast, penetration and fragmentation, non-lethal weapons have rela-tively reversible effects and affect objects differently (Alexander et al., 1996).

13.2.1 Blast Wave Projector

Energy generation from a pulsed laser that will project a hot, high pressure plasma in the air infront of a target It creates a blast wave with variable but controlled effects on hardware and troops(Alexander et al., 1996)

This could be akin to cavitation bubbles that are the loudest source of sound from shippropellers

Snapping shrimps (Stomatopods or mantis shrimp) are very noisy; it has been long assumed thatthe noise was caused by their claws closing InOdontodactylus scyllarus, the sound is caused by thecollapse of cavitation bubbles due to the high speed at which the claw moves, powered by a highlyelastic part of the exoskeleton The shrimps appear to use cavitation to stun their prey (small crabs,fish, and worms); it certainly wreaks havoc with the shrimp’s own exoskeleton Although the claw

is highly mineralized, its surface becomes pitted and damaged; stomatopods moult frequently andproduce a new smashing surface every few months (Patek et al., 2004)

13.2.2 Infrasound

Very low-frequency sound that can travel long distances and easily penetrate most buildings andvehicles Transmission of long wavelength sound creates biophysical effects; nausea, loss ofbowels, disorientation, vomiting, potential internal organ damage or death may occur Superior

to ultrasound because it is ‘‘in band’’ meaning that its does not lose its properties when it changesmediums such as from air to tissue By 1972 an infrasound generator had been built in France thatgenerated waves at 7 Hz When activated it made the people in range sick for hours (Alexander

et al., 1996)

Whales are certainly able to generate low frequencies (15 to 30 Hz) which they use forcommunication over long distances (the capercaillie, a ground-living bird of the Scottish wood-lands, uses low frequencies for the same reason) but they have not been tested for any damagingeffects (Croll et al., 2002)

Although it does not really belong to ‘‘infrasound,’’ animals (e.g., frogs, birds, and deer)advertize a false impression of exaggerated size by making low frequency sounds (Reby andMcComb, 2003) The implication for other animals is that a low noise can only come from alarge resonant cavity, so the animal producing the noise is probably large and therefore probablystrong Producing low frequency vibrations is therefore a premium especially if the animal cannot

be seen and the assessment of size can be made only from the frequency range of the noise.13.2.3 Squawk Box

Crowd dispersal weapon field tested by the British Army in Ireland in 1973 This directional deviceemits two ultrasonic frequencies which when mixed in the human ear become intolerable Itproduces giddiness, nausea or fainting The beam is so small that it can be directed at specificindividuals (Alexander et al., 1996)

There are many reports of dolphins using a similar technique, either when hunting or whenswearing at a human experimenter In a U.K radio programme some years ago, a researcherrecounted playing back its own sounds to a dolphin to see what it would do, including listening

to the dolphin’s response with a hydrophone The dolphin was quite amenable to this game andcooperated well But by mistake the experimenter sent the dolphin a rather loud signal to whichthe dolphin obviously objected The dolphin looked at the experimenter through the walls of theaquarium, then went to the hydrophone and blasted into it before the experimenter could rip off hisearphones The experimenter experienced much pain! The implication is that we could probablylearn about physiologically damaging noise from dolphins and other cetaceans that are also muchmore experienced with the technique, having been using it for longer than we have.

13.3.1 Body Armor

Many animals have a hard outer covering that serves as armor, but there are many different ways inwhich the function is realized Whereas the armor developed for individuals or vehicles is based onthe inevitability of attack, and relies on resisting by strength, biological armor can come in manyguises Obvious ones are armadillo and tortoise, although nobody seems to have made anymeasurements of the protection that is given The same is not true of ankylosaurs (Figure 13.1)and their relatives, herbivorous dinosaurs that grew to 10 m long during the late Jurassic andCretaceous They had centimeter-sized osteodermal plates that covered back, neck, head, and alsoprotected the eyes In polarized light, sections of the plates show where collagen — a normalprecursor of bone and an essential component of skin — was incorporated Comparing similardermal bones from stegosaurus and crocodile, the polocanthids had extra collagen fibres that mayhave stabilized the edges of the bony plates But in nodosaurids — which also had plates between 2

and 5 cm thick, the collagen fibres ran parallel and perpendicular to the surface, and then at 458 to

each of these axes, providing reinforcement in all directions Ankylosaurids had thinner plates thatwere 0.5 to 1.0 cm thick, convex shaped, which will have increased their stiffness in bending, andwith the collagen fibres randomly arranged

The dinosaur structure seems to be repeated in the bone-free collagenous skin of the whiterhinoceros, which is three times thicker and contains a dense and highly ordered three-dimensionalarray of relatively straight and highly crosslinked collagen fibres The skin of the back and sides

of the animal is therefore relatively stiff (240 MPa) and strong (30 MPa), with high breakingenergy (3 MJ m
3) and work of fracture (78 kJ m
2) These properties fall between those of tendonand skin as would be expected from a material with a large amount of collagen (Shadwick

et al., 1992)

Figure 13.1 An ankylosaur.

Unfortunately the data on ‘‘soft’’ body armor (e.g., Kevlar) does not quote performance in theseunits, preferring to equate energy of an incoming threat to depth of penetration through the armor.Presumably one has to go to reports from the old big game hunters to get similar information aboutthe rhinoceros However, leather is still tougher than Kevlar, although nobody really understandswhy, since the collagen fibres are not dissimilar from Kevlar in general morphology.

A concept that is entirely alien to the current design of man-made armor is the porcupine quill,although the pikestaff of the medieval infantryman might be considered analogous, and parts ofmediaeval armor and their weapons were equipped with spikes to keep the enemy at bay Theporcupine has several different types of quill; those with a length-to-diameter ratio greater thanabout 25 are mostly rattles to warn enemies that there are quills here Those with a lower length-to-diameter ratio (15 or less) act as columns when they meet an end load, and with the sharp tip, caneasily penetrate flesh They are sometimes brittle and the tip can break off, but they also have weakroots in the porcupine’s skin and so can easily be pulled out when the impaled attacker moves away.The quills are filled with a variety of reinforcing foams, struts, and stringers, so that they rarelybreak when buckled (Vincent and Owers, 1986) Quills are modified hairs and are made of keratin

In general, plants have totally passive defense mechanisms, which is energetically probablymuch cheaper They are thus built to survive a certain amount of damage due to grazing, and mayeven grow more vigorously in response Many plants, especially those living under dry conditions,such as the acacia, have spines, thorns, or hooks that cause pain to the animals attacking them.Presumably the giraffe, which feeds on such plants, has a reinforced surface to its tongue so that itcan cope with the abuse Many of the grain-bearing plants (Graminae) have silica particles —sometimes as much as 15% of the dry weight — which wears down the teeth of the animals feeding

on them Indeed the performance of the teeth is frequently dependent on such wear, exposing acomplex of self-sharpening cutting and grinding surfaces (Alexander, 1983) The literature onplant–animal interactions is large, mostly concerned with how plants control the ease with whichthey can be grazed, commonly by limiting crack propagation with inhomogeneities such asembedded fibres; and their chemical defenses which range from repulsive taste or smell, throughmanipulation of the digestion or behavior of the grazer (by psychoactive drugs) to lethal chemicals,mostly in those plants which cannot afford to be eaten since they grow so slowly

In both plants and animals, spines and thorns are passive and are of use only at close quarters.The closest equivalent is barbed wire which many claim to be biomimetic

Horns and antlers can be used for both attack and defense, an unusual concept for technology —the closest analogy is the sword, which can be used both to deliver a blow and to parry one Theutility of antlers (dead, made of bone, replaced each season, grown from the tip) and horns (living,made of a thick keratin sheath over a bone core, incremented each season, grown from the base) hasbeen questioned by animal behaviorists who find difficulty coping with the wide range in sizes ofhorns and antlers, and the range in forces imposed on them during fighting These problems werelargely resolved by Kitchener, who showed that there is a linear relationship between the secondmoment of area at the base of the horn or antler and the body weight of the animal, and that thisrelationship is constant for any single style of fighting Most styles are ritualistic and akin towrestling; sheep and goats are far more agonistic, throwing themselves at each other resulting inmore random forces being exerted on their horns (Kitchener, 1991)

Ever since their discovery in the 16th century, the enormous antlers of the extinct Irish elk orgiant deer (Megaloceros giganteus) have attracted scientific attention Mechanical analysis of theantlers of the Irish elk shows that they are massively over-designed for display (for which, as JohnCurrey pointed out, they really only need to be made of waterproof cardboard) because the forceexerted by gravity acting on the antlers is less than 1% of their strength In contrast, the antlers seem

to be optimally designed for taking the maximum estimated forces of fighting, that are more than50% of the strength of the antler, as would be expected for a biological structure of this kind.However, this analysis assumes that the mechanical properties of the bone of the Irish elk antlersand living deer are similar It would be unwise to measure directly the mechanical properties of

Irish elk antler after more than 10,000 years in a peat bog Instead, neutron diffraction, whichmeasures the degree of preferred orientation of the hydroxyapatite crystals that comprise bone,showed that the orientation of the hydroxapatite is predictable from the presumed forces generatedduring fighting Thus on the tensile faces of the antler, the orientation was along the length of theantler, whereas on the compressive faces, the orientation was more orthogonal to the long axis —exactly what the theory of fibrous composite materials predicts (Kitchener et al., 1994).

Many animals and plants, especially insects, can look like inert objects such as bits of wood

or stones (e.g., the succulent South American plant Lithops) Because of their colored wings,many moths can conceal themselves when placed against a suitable background such as the bark

of a tree The peppered moth (Biston betularia) in industrial areas of England has been held

as a classic example of natural selection, with birds eating those moths that they could seeonly when they were sitting on an unsuitably colored bark In this instance the moth wasoriginally light with small black speckling, but pollution produced in the early industrial revolutionblackened the trees, so an initially rare dark form of the moth was selected by being less easily seenand eaten (Kettlewell, 1955) Later, with reduced pollution and clearing of the woods, the bark waslighter and better lit and the lighter-colored form again predominated Similarly many nesting birdsare difficult to see; ground-nesting birds have camouflaged eggs and chicks Many insects,especially grasshoppers, have bright hind wings which disappear when the insect stops flying,settles, and folds its wings thus becoming camouflaged This sudden change makes it difficult tospot the insect

Another basic component of passive camouflage, well known to technology, is countershading,

in which, those parts of the body that are normally well illuminated are darkly colored, and thosethat are normally shaded lightly colored This is seen in both terrestrial and aquatic animals; thecorollary is the larva of the privet hawk moth (Sphinx ligustri) which is dark on the underside andlight on the upperside, and habitually hangs inverted beneath its twig The effect is to flatten theaspect of the animal, making it difficult to judge its size and how far away it is

The literature of camouflage in biology is very large (Wickler, 1968)

13.3.3 Warning Coloration

The announcement that you are strong or dangerous is useful since it can deter an enemy fromattacking, and gains its best effect by the strong making themselves easily seen But one can alsopretend strength This is not novel, and has been used for hundreds of years with armies makingthemselves appear larger than they are with hats on sticks, unattended guns protruding through thebattlements, and soldiers circulating past a small gap for the enemy to see

Many animals and plants (especially fruits) advertize that they are poisonous or that they have

a very nasty sting or bite Typical warning colors are bright, for instance red and yellow associatedwith black, mutually arranged to maximize contrast and visibility (aposematic coloration) There is

a vast amount of literature on this aspect of coloration, which includes mimicking of an unpalatableanimal by a palatable one (Batesian mimicry) and mimicry of palatable mimics of unpalatableanimals (Mu¨llerian mimicry) Such mimicry is probably commonest amongst butterflies, where themain selection agent is predatory birds and the habitat is thick forest or woodland (Wickler, 1968).Thus, the predatory bird probably only ever gets a fleeting glimpse, poorly illuminated of itsprospective prey, and with this minimal information it has to decide whether or not to attack It

is imaginable that under these conditions even a slight resemblance to an unpleasant species isenough to convince a bird not to attack.

Most insects, in particular beetles, butterflies, and moths, get their noxious chemicals from theplants they feed on The first bird to be discovered with warning coloration and toxic feathers is thePitohui of New Guinea (Dumbacher et al., 2004) The source of the alkaloids, also found in poison-dart frogs, is Melyrid beetles

13.3.4 Active Camouflage

Created by dynamically matching the object to be camouflaged to its background colors and lightlevels thus rendering it virtually invisible to the eye This is conceptually the same camouflageprocess as that used by a chameleon This is accomplished through a sophisticated color and lightsensor array that detects an object’s background color and brightness This data is then computermatched and reproduced on a pixel array covering the viewing service of the object to becamouflaged

Pattern control is achieved by flatfish such as the plaice (Pleuronectes platessa) that can changeits shading and patterns to suit a variety of backgrounds — including a chequer board! However, itcan manage only black and white, and then only slowly, over a matter of minutes, since its color-change cells (melanophores) are hormonally controlled They change color by moving pigmentaround inside the cell going from ‘‘concentrated’’ (the pigment is centered making the cell white ortranslucent) to ‘‘dispersed’’ (the pigment is spread around the cell which now appears dark) (Fuji,2000; Ramachandran et al., 1996)

Color control in octopus and squid (cephalopod — literally ‘‘head-footed’’ — molluscs) ismanaged by colored cells — chromatophores — that are found in the outer layers of the skin Eachcomprises an elastic sac containing pigment to which is attached radial muscles When the musclescontract, the chromatophore is expanded and the color is displayed; when they relax, the elastic sacretracts The chromatophore muscles are controlled by the nervous system Differently colored(red, orange, and yellow) chromatophores are arranged precisely with respect to each other, and toreflecting cells (iridophores producing structural greens, cyans and blues, and leucophores, reflectincident light of whatever wavelength over the entire spectrum) beneath them Neural control of thechromatophores enables a cephalopod to change its appearance almost instantaneously (Hanlon

et al., 1999), a key feature in some escape behaviors and during fighting signalling Amazingly theentire system apparently operates without feedback from sight or touch (Messenger, 2001).The primary function of the chromatophores is to match the brightness of the background and

to help the animal resemble the substrate or break up the outline of the body Because the tophores are neurally controlled, the animal can, at any moment, select and exhibit one particularbody pattern out of many, which presumably makes it difficult for the predator to decide orrecognize what it is looking at When this is associated with changes in shape or behavior, theprey can become totally confusing Consider this performance by an octopus found in Indo-Malaysian waters It is seen on the seabed as a flatfish and swims away with characteristic

chroma-‘‘vertical’’ (remember the flatfish swims on its side) undulations As it does so it changes into apoisonous zebra fish It then dives into a hole and sends out two arms in opposite directions tomimic the front and back ends of a poisonous banded sea snake (videos of these behavior patternsare available to download with the paper by Norman et al.) It also sits on the sea bed with its armsraised, possibly in imitation of a large poisonous sea anemone Or it can sink slowly through thewater column apparently imitating a jellyfish (Norman et al., 2001) Each of these types of animalrequires a different response on the part of the predator, which presumably is totally confused Suchdynamic mimicry is seen only in cephalopods and the films of the Marx Brothers

Countershading in animals is widespread and cephalopods are no exception On the ventralsurface, the chromatophores are generally sparse, sometimes with iridophores to enhance reflec-tion; dorsally the chromatophores are much more numerous and tend to be maintained tonically

expanded More remarkably, however, cephalopods can maintain countershading when theybecome disorientated The countershading reflex ensures that chromatophores on the ventralsurface of the entire body expand when the animal rolls over on its back: a half-roll elicitsexpansion of the chromatophores only on the upper half of the ventral body Such a response is,

of course, possible only in an animal whose chromatophores are neurally controlled (Ferguson et al.,1994) When matching brightness, the chromatophores act like a half-tone screen; color matching isachieved with the chromatophores, iridophores, and leucophores (Hanlon and Messenger, 1988)

On variegated backgrounds, a cuttlefish will adopt the disruptive body pattern, whose effect is

to break up the ‘‘wholeness’’ of the animal (Figure 13.2) Disruptive coloration is a concealmenttechnique widespread among animals Octopus vulgaris has conspicuous frontal white spots;loliginid squids show transverse dark bands around the mantle that probably render the animalless conspicuous, and the harlequin octopuses have bold black-and-white stripes and spots.Although many animals use patterning for concealment, it is nearly always a fixed pattern.Because they control their chromatophores with nerves and muscles, cephalopods can select one ofseveral body patterns to use on a particular background

Cephalopods also produce threatening or frightening displays In its extreme form, the animalspreads and flattens, becoming pale in the middle and dark around the edges, creating dark ringsaround the eyes and dilating the pupil, and in sepioids and squids, creating large dark eyespots onthe mantle This effect is extremely startling The animal also seems to get bigger

13.3.5 Translucent Camouflage

The best way to avoid being seen is to be invisible and so cast no shadow The equivalent oftranslucence is to present the observer with the scene which the object is blocking out In atechnical world this can be done using a camera to film the scene that is blocked and presenting

it to the observer in front of the object

Whole animals (e.g pelagic marine organisms such as jelly fish, sea gooseberries, and manylarval forms) or parts of animals (e.g the cornea of the eye) can be translucent and therefore nearlyinvisible To be translucent, reflection of incident light must be kept to a minimum and light must

be neither scattered nor absorbed as it passes through the body Scattering is caused by variations

in refractive index Animal tissue normally has many variations in refractive index (cells, fibres,nuclei, nerves, and so on) The most important factors are the distribution and size of thecomponents; refractive index is less important; the shape of the components is least important.For instance, if a cell requires a certain volume of fat to survive but must scatter as little light as

Figure 13.2 (See color insert following page 302) A cuttlefish (Sepia officinalis) can change its appearance according to the background Here the animal changes its body pattern when moved from a sandy or gravel substrate

to one with shells (Courtesy of Roger T Hanlon, Senior Scientist, Marine Biological Laboratory, Woods Hole, MA.)

possible, it is best to divide the fat into many very small droplets Slightly worse is to divide it into afew large droplets, but the very worst is to divide it into drops about the size of the wavelength oflight (Johnsen, 2001).

Variations in refractive index do not always cause scattering If the refractive indices vary byless than half the wavelength of light, the scattered light is eliminated by destructive interferenceand the light waves overlap in such a way that they cancel each another This happens in the cornea

of the eye, which is constructed of an orthogonal array of collagen fibres

Many organisms living in the deeper ocean, where there is little or no ambient light to bereflected or by which camouflage color can be seen, produce their own light The organs that do this

— photophores — can be mounted on mechanisms which rotate them so that they face the body andare effectively obscured, hence can be modulated and switched on and off (Johnsen et al., 2004).13.3.6 Reflecting Camouflage

If an object can simply reflect the color and pattern of its surroundings, then it will be adaptive But

if it merely reflects the sky when looked at from above, or the ground when looked at from below,this will be ineffective The geometry of the reflecting surface is crucial In deep water, the laterallyscattered light is equal in intensity from a range of angles Looking up, one sees brightness; lookingdown there is dim blue-green A perfect mirror suspended vertically in the water would be invisiblesince the light from the surface is reflected to a viewer below, making the mirror appear translucent.Many fish have platelets of guanine in their scales arranged vertically, thus generating such a mirrorindependently of the shape of the section of the body The fish is also countershaded Viewedlaterally the fish is a reflector and therefore invisible Viewed from the top, it is dark like the depthsbelow it Viewed from below it is silvery white like the surface

The most difficult view to camouflage is that from directly below when the fish obscures lightfrom above Many clupeids, such as the threadfin shagDorosoma petense, are thin and come to asharp edge at the belly This allows light from above to be reflected vertically downwards over theentire outline (Johnsen, 2002)

Another form of reflecting camouflage is provided by the cuticle of some scarab beetles Thecuticle is made of structures that look like liquid crystals, mainly nematic and cholesteric Thus, ofthe incident light on the cuticle, the right circularly polarized component can be reflected and theleft circularly polarized light can penetrate the helicoidally structured cuticle However, at a certaindepth, there is a layer of nematic structure that acts as a half-wave plate, reversing the sense ofpolarization of the light, which is then reflected when it reaches the next layer of helicoidalstructure, has its sense of polarization reversed again by the nematic layer, and continues backout through the helicoidal cuticle with very little loss The refractive index of the cuticle isincreased by the addition of uric acid Thus the cuticle is an almost perfect reflector, making thebeetle appear the same green as its surroundings This system will work only when the color andlight intensity are the same in all directions (Caveney, 1971)

13.3.7 Motion Camouflage

This is included here since it is a way of observing and approaching an object without making itobvious to an observer or the object that it is being observed The technique might have beenunintentionally deployed by attacking fighter aircraft, and is currently in development for disguis-ing the intended target of guided missiles An everyday equivalent, converted to the acousticenvironment, would be that if you are following someone closely, make sure that the noise ofyour footfall is in synchrony with that of your quarry

This is a stealth shadowing technique used by, for instance, the dragonfly approaching its prey

on the wing The dragonfly follows a path such that it always lies on a line connecting itself and afixed point Then the only visual cue to the dragonfly’s approach is its looming (i.e., the increase in

the size of its image as it closes in on the object) The observer of the object thus sees no movementaway from the direction of the fixed point The fixed point could be a part of the background againstwhich the dragonfly is camouflaged, or the initial position of the dragonfly, in which case thedragonfly appears not to have moved from its starting point (Anderson and McOwan, 2003).13.3.8 False Target Generation

A device that creates and presents an image of a target that causes a weapon to aim at a falsetarget Used as a countermeasure to precision guided weapons (Alexander et al., 1996)

This is a common ploy in insects; for instance, butterflies have eye spots on the trailing edge ofthe hind wing Predating birds tend to aim for the eyes rather than the body of the insect, and so theinsect escapes with relatively slight damage to the hind wing Similarly fish can have an eyespot onthe tail fin with the true eye concealed in a dark marking across the head A number of moth larvaehave a false ‘‘head’’ at the tail end which can simply be eye spots or an image of the head of anotheranimal such as a snake The advantage then is not just that the attack will be at the ‘‘wrong’’ end ofthe animal, thus protecting the nervous system, but that the animal will apparently move backwards

13.4.1 Slick Coating

Teflon lubricants that create a slippery surface because of their chemical properties Thesechemical agents reduce friction with the intent to inhibit the free movement of the target In the1960s Riotril (‘‘Instant Banana Peel’’) was applied as an ostensibly inert white powder to a hardsurface and wetted down It then became like an ice slick It is virtually impossible for an individual

to move or stand up on a hard surface so treated; tyres skid Riotril, if allowed to dry, can easily bepeeled away or, because it’s water-soluble, can be washed away (Alexander et al., 1996)

A similar phenomenon is found in the carnivorous pitcher plants (Figure 13.3) Severalmechanisms have been proposed for the way they capture insects, mostly slippery surface waxcrystals But the important capture mechanism is due to the surface properties of the rim of thepitcher, which has smooth radial ridges This surface is completely wettable by nectar secreted bythe rim, and by rain water, so that a film of liquid covers the surface when the weather is humid Therim is then slippery both for soft adhesive pads (the liquid sees to that) and for the claws, due to thesurface topography This dual system starts sliding ants down the slippery slope (Bohn and Federle,2004)

The Peripatus (the velvet worm, Figure 13.4) shoots out sticky adhesive threads that entangleits prey The threads contain protein, sugar, lipid, and a surfactant, nonylphenol The proteinsare the principal component of the slime; the amino acid composition suggests collagen Theoriginal function of the secretion was probably defense, developing into attack as the viscosity,amount, and distance that the substance could be expelled all increased This defensive substancewould in turn be also useful for hunting, if the original condition consisted of capturing preydirectly using mandibles, as when onychophorans handle small prey The adhesive substanceprobably allows the entanglement of larger and therefore more nutritious prey (Benkendorff et al.,1999).

When in danger, some species discharge sticky threads that can entangle predators Some likethe sea cucumber can even expel their internal organs, which they regrow causing it no harm at all.Although the mechanical properties of the threads have not been measured, they are obviously very

Figure 13.3 A pitcher plant trap, which is a modified leaf The rim of the trap is curled over, forming a slippery platform onto which insects can walk.

Figure 13.4 The velvet worm, Peripatus capensis It lives in damp places and has no external armor However, it can shoot sticky threads several times its body length.

tough since the Palauan people of the south Pacific squeeze the sea cucumber until it squirts out itssticky threads, which they put on their feet to protect them when they walk around the reef.When attacked, the centipedeHenia rolls itself up with its ventral surface facing outward This

is the opposite to most centipedes, which either attack with their large mandibles or roll up withtheir dorsal surface — the most armored — facing outward However,Henia has a large gland onthe underside of each segment which secretes an adhesive The amount of adhesive is more than10% of the body weight The adhesive sticks to the mouthparts, etc., of the assailant preventing theparts from working While, the assailant retires to clean itself, the centipede escapes The glueseems to be made of two components: a fibrous protein (possibly silk-like) and a globular protein,which is the actual adhesive At high magnification, the adhesive appears as a large number of finefibres stuck firmly at each end Thus removing the adhesive is not as simple as initiating a crack andpropagating it; each fibre has to be broken separately, taking a lot of time and effort (Hopkin et al.,1990) The adhesive can stick to dirty wet surfaces, desirable for any technical adhesive Whensticking two glass plates together it is as effective as a cyanoacrylate adhesive

13.4.3 Sticky Foam

A name given to a polymer-based superadhesive agent The technology first began appearing incommercial applications such as ‘‘super glue’’ and quick setting foam insulation It is extremelypersistent and is virtually impossible to remove Sticky foam came to public attention on February

28, 1995 when U.S Marines used it in Mogadishu, Somalia, to prevent armed intruders fromimpeding efforts to extricate United Nation forces from that country (Alexander et al., 1996)

A foam allows a limited amount of material to occupy a greater volume, and since the intent is toimpede rather than to entrap, the greater difficulty of breaking a structure that can accommodatehigher strains, and is made of multiple threads, contributes to the effectiveness of the mechanism.This is probably why it occurs in the adhesive plaque which sticks the byssus thread of the musselonto the rock Otherwise, foams in biology are more used for protection than for attack and are anintegral part of many egg cases, especially in snails and insects (e.g.,Mantis, Locusta) They arecommonly made of protein, often phenolically tanned and waterproofed, although their primarystability comes from their liquid crystalline structure (Neville, 1993)

13.4.4 Rope

Nylon rope dispersed by a compressed air launcher mounted on a truck (Alexander et al., 1996).With animals the rope can become part of an entrapment mechanism — basically with anadhesive device on the end of the rope Examples are the ballistic snares of the chameleon and thesquid

In the arms of the squid, transverse muscle provides the support required for the relatively slowbending movements while in the tentacles the transverse muscle is responsible for the extremelyrapid elongation that occurs during prey capture In the squidLoligo pealei, the thick filaments ofthe obliquely striated muscle fibres of the arms are approximately 7.4 mm long while those in thecross-striated fibres of the tentacle are approximately 0.8 mm long This results in more serieselements per unit length of fibre Since shortening velocities of elements in series are additive, thisresults in the shortening velocity of the tentacle fibres to be approximately 15 L0s
1compared withthe arm transverse muscle 1.5 L0s
1 at 198C.

The strike ofL pealei when it is capturing its prey takes as little as 20 ms During the strike, theproximal portion of the tentacle, the stalk, elongates The nonextensible distal portion of thetentacle, the club, contacts the prey and attaches using suckers Extension takes 20 to 40 ms withpeak strains in the stalk of 0.43 to 0.8 Peak longitudinal strain rates vary from 23 to 45 s
1 Thestalk can extend at over 2 ms
1at an acceleration of 250 ms
2 Once the tentacular clubs havecontacted the prey, the stalks often buckle (Kier and Thompson, 2003)

13.4.5 Smoke

A thick, disorienting ‘‘cold smoke’’ that can be generated in areas from 2,000 to 50,000 cubic feet Itrestricts an intruders eye–hand coordination and interactions among members of an intrudinggroup White obscuring smoke can be delivered by grenades or smoke pots Relatively inexpensive,noncontaminating and tactically ideal for police use Obscuring smokes are temporarily irritating

to the nose and throat and cause those affected to lose their senses of purpose and direction(Alexander et al., 1996)

Compared to smell, all the intricate color and shape changes of the octopus are ineffective Oneway to counter this threat is to block the predator’s sense of smell, which has been shown to be oneway in which the ink is used, though in large quantities Obviously ink can be used to cover theanimal’s hasty departure, but it can also be used as a decoy, since the octopus or cuttlefish canproduce a coherent plume of ink that is more or less of its own size and shape

13.4.6 Stakes

A sharp stake, often of wood or bamboo, that is concealed in high grass, deep mud or pits It is oftencoated with excrement, and intended to wound and infect the feet of enemy soldiers Can be utilizedboth as a booby trap and as a barrier Commonly known as punji stick or punji stakes (Alexander

et al., 1996)

The Komodo Dragon, Varanus komodoensis, the largest land-living lizard, feeds mainly oncarrion Even though it is large and strong, mostly when it attacks living animals, it only woundsrather than kills them But even minor wounds often become septic, so septicemia seems to be asignificant mechanism for weakening and eventually killing prey However, when the dragons fighteach other, they appear to suffer no ill effects, even though their fights are frequent and often result

in deep puncture wounds If one could identify the bacteria in the dragon’s saliva, including thosecapable of killing its mammalian prey, then one might have not only a chemical weapon but also itsantidote Additionally the wounds made by the dragon bleed profusely and it takes longer for theblood to clot, so the saliva also contains an anticoagulant

13.5.1 Hypodermic Syringe or Dart

Modified shotgun or handgun in which the projectile is a drug-filled syringe activated by a smallcharge on impact Wide variety of drugs available including emetics (Alexander et al., 1996).Organisms have two methods of delivering poison: externally (on being attacked) and internally(on being eaten) Since plants can usually afford to lose a leaf or two, they tend to have the poisonsinternally and are not necessarily brightly colored as warning Animals are either brightly colored(for instance, the poison-dart frogs,Dendrobates spp or poisonous nudibranchs or insects, q.v.) orcarry their poisons in spines or stings Bees, wasps, and scorpions are obvious examples of thelatter; the sting is deployed, penetrates the victim with effort from the stinger, and poison is injectedfrom a sac which contracts In hive bees and presumably others, the sting sac also releases apheromone which attracts other bees and encourages them to sting — rather like a beacon or markerused in bombing raids The urticaceous hair found on stinging nettles (Urtica spp.) and manycaterpillars is a passive mechanism On the stinging nettle there are hollow hairs (Figure 13.5)containing several irritating substances such as histamine (the mediator of some allergic reactions),serotonin, acetylcholine, and formic acid When lightly brushed against, the tip of the hair (made ofbrittle silica) snaps off at an angle leaving a sharp tip that pierces the skin and delivers the cocktail

A similar system operates in caterpillars The urticating hairs or spines of the larva of the moth

Automeris io (which is related to silkworms) are of two types, both having a poison gland (Gilmer,1925) The chemical nature of the poisons is not fully known, though they can contain formic acid,histamines, and enzymes which can dissolve human tissues and cause dermatitis The spines workvery much like nettle stings Severe allergic reaction can cause death The skin bleeds after contactwith caterpillars of the VenezuelanLonomia achelous which have poison spines containing ananticoagulant.

13.5.2 Neuro-Implant

Computer implants into the brain that allow for behavioural modification and control Currentresearch is experimental in nature and focuses on lab animals such as mice (Alexander et al.,1996)

There are several (probably many) parasites which affect the behavior of the host to the benefit

of the parasite The parasite can therefore be thought of reprogramming its host, though of coursethe effective agent, being chemical, is far more subtle and would be much easier to administer.ConsiderDicrocoelium dendriticum, a parasitic worm; its main or primary host is sheep The eggsare released in the dung of the sheep and are eaten by the snailCionella lubrica The eggs developand the next stage (cercaria) is released into the snails mucus slime balls (which form in itsrespiratory chamber) and deposited on vegetation Ants (Formica fusca) then eat the slime balls.Most of the cercaria become dormant in the ant’s abdomen However, some of them migrate intothe ant’s head where they enter the nervous system of the ant and affect its behavior As eveningapproaches and the air cools, the infected ants, instead of returning to their nest, climb to the top of

Figure 13.5 A nettle sting, about 1-mm long The tip is highly silicious and brittle, so that when it breaks off it leaves a sharp end like a syringe needle It contains an irritant poison.

the vegetation and clamp on to the leaves with their mandibles They stay there immobile until thenext morning The ants are thus likely to be eaten by passing sheep, thus completing the life cycle ofthe parasite Although the parasite is obviously far more complex than a computer chip, the change

in the ant’s behavior is minimal: the interaction of the insect’s temperature response with itsresponse to gravity

13.5.3 Pheromones

The chemical substances released by animals to influence physiology or behavior of other members

of the same species One use of pheromones, at the most elemental level, could be to mark targetindividuals and then release bees to attack them This would result in forcing them to exit an area orabandon resistance (Alexander et al., 1996)

Lima beans (Phaseolus lunatus) infested with spider mites release chemicals that attract tory mites that then prey on the spider mites The uninfected plants downwind also attract predatorymites Jasmonic acid sprayed onto tomato plants may regulate volatiles that attract parasitoidwasps that prey on caterpillars feeding on the tomato plants Such indirect defenses may beeven more complex This may then be why some plants house and feed the predators as hashappened in ant plants The ants can be considered to be an induced biotic defense because thenumber of ants that patrol the leaves increases severalfold as a result of attraction by volatilesemitted from the damaged tissue when a herbivore chews a leaf The ants are acting as a Praetorianbody guard

Human technology used elastic mechanisms as power amplification of human or animal energy tolaunch arrows and other projectiles; this approach is used in nature but man has replaced elasticmechanisms with explosives

The ability to escape quickly from a predator is vital for most prey,while predators have obviousadvantages if they are able to outrun fast prey and overpower it using even faster weapons.The speed of running, jumping, predatory strikes, etc is generally correlated with the animal’ssize In order to achieve velocities comparable to those of larger animals, small ones such asmost arthropods have to rely on very high accelerations (Alexander and Bennet-Clark, 1977).Therefore, in many insects, the speed of action reaches or even surpasses the velocity limitationsinherent in muscle contraction Irrespective of phylogenetic relationships, convergent evolution hasresulted in special mechanical designs (e.g., springs or catapults) that overcome the constraints ofmuscle action in many arthropods (Bennet-Clark and Lucey, 1967)

In addition to fast mechanics, both prey and predators rely on rapid neuronal and muscularsystems to initiate and control their swift escape or predatory actions Among the ants, severalspecies employ particularly fast mandible strikes in order to catch swift prey or to defendthemselves This so-called trap-jaw mechanism (a mandible strike which far exceeds the speedallowed for by muscular contraction) has evolved independently in three ant species (Gronenberg,1996) These studies reveal that the fast strike results from energy storage in a catapult design, andits control relies on fast neurones and on a high velocity trigger muscle

In biological elastic mechanisms, strain energy is stored only when the spring mechanism is

in the position from which the energy will be released — its loaded configuration This is incontradistinction to most man-made systems, where the assumption of the loaded configuration

is also the means by which the energy is stored (e.g., drawing a bow) For instance, the locustbrings its legs into the jumping position, then loads the main jumping tendon using muscle power.This probably makes the system safer and allows a lower safety factor in the strength of thecomponents (Bennet-Clark, 1975)

Nature commonly uses bistable mechanisms This is intimately associated with the separation

of the assumption of the loaded configuration from the storage of strain energy The mechanism

is drawn over center by the main spring, and then the spring is loaded The main spring has a lowmechanical advantage and can store a large amount of strain energy, generating high forces.When the system is ‘‘fired’’ the trigger, which can generate only a low force but has a highmechanical advantage, allows the mechanism to move back over center and the energy from themain spring is fed into the system (Bennet-Clark and Lucey, 1967) This has the advantage thatthere are no firing pins or hooks to jam or break Thus, control is smoother and reliabilityimproved In the snap-jaw ant, the mandibles are clicked against each other, rather like snappingfinger and thumb over each other The ant can then move comparatively massive objects Themandibles are first held with the tips just touching, then loaded Large muscles contract againstthe closed mandibles that are thus bent and store some elastic energy However, most of themuscular energy is transformed and elastically stored within the apodeme and its cuticularthreads, within the muscle fibres and probably also within the entire head capsule Slight rotation

of one of the mandibles then causes its lower edge to bend slightly inwards and lets the othermandible slide above it, powered by the strain energy stored within the contracted muscles andthe mandible shaft (Gronenberg et al., 1998) Immediately afterwards the unstimulated mandiblehits the object and bounces it away The stored energy thus is spent and the mandibles aredecelerated during the second half of their trajectory and come to a hold before they could bumpinto the front of the head

The Venus fly trap (Dionaea muscipula) preys on insects and other small animals that ventureonto its trap leaves and trigger their closure by disturbing certain sensitive hairs The leavesroutinely shut in 1/25 s Such speed of movement is uncommon amongst plants and so has attractedattention and theories for many years The mechanism is based on a turgor-driven elastic instability

of the leaf, which is in effect a prestressed mechanical bistable structure (Forterre et al., 2005;Thom, 1975) A better understanding of this mechanism and the way in which it is designed andactuated would not only solve a long-standing conundrum, but could also give rise to a series ofnovel hydraulic actuators and switches

Nature does use explosives, in the sense that an explosive chemical reaction proceeds at veryhigh speed, is exothermic, and produces large amounts of hot gas that do the damage The insect

in question is the bombardier beetle, of which there are many species, for example Brachinusexplodens, which produces a jet of steam and hydroquinone at a temperature probably in excess of

1008C The propellant is oxygen produced from the breakdown of hydrogen peroxide The jet is

pulsed (at about 500 Hz) and can, depending on the species of beetle, be aimed very accurately(Dean et al., 1990)

is used for navigational signals The large battery and the other small one are used to generate thestunning discharge After delivering a strong shock, the electric eel must then allow the electricorgan to recharge (Heiligenberg, 1977)