Deadly strike mechanism of a mantis shrimp
This shrimp packs a punch powerful enough to smash its prey’s shell underwater.
S. N. Patek, W. L. Korff, R. L. Caldwell
Department of Integrative Biology, University of
California, Berkeley, California 94720-3140, USA
Nature
Vol. 428
April 22, 2004
Stomatopods (mantis shrimp) are well known for the feeding appendages they use to smash shells and impale fish. Here we show that the peacock mantis shrimp (Odontodactylus scyllarus) generates an extremely fast strike that requires major energy storage and release, which we explain in terms of a saddle-shaped exoskeletal spring mechanism. High-speed images reveal the formation and collapse of vapour bubbles next to the prey due to swift movement of the appendage towards it, indi-cating that O. scyllarus may use destructive cavitation forces to damage its prey.
Stomatopod appendages were previously thought to be limited to a maximum speed of 10 m s-1(1) but, by using new imaging technology and a faster species, we have measured the dactyl heel reaching peak speeds of 14–23 m s-1, peak angular speeds of 670–990 rad s-1, and peak acceleration of 65–104 km s-2 within an average period of 2.7 ms, making O. scyllarus perhaps the fastest appendicular striker in the animal kingdom.
To generate these extreme movements in water, a large amount of energy must be released over a short period. Stomatopods increase their power output through the use of a click mechanism, in which latches prevent appendage movement until muscle contraction is maximal(1,2). When the latch is freed, stored energy is released over a shorter time than the duration of the original muscle contraction. Some extreme animal movements also require a specialized spring, because the muscle fibres and tendon store insufficient elastic strain energy(3–5). We conservatively calculate that a minimum power requirement of 4.7 x 10-5 watts per kilogram of muscle is necessary for a typical strike, which is orders of magnitude higher than that available in the fastest-contracting muscles(3,6) known. Moreover, the lateral extensor muscle and apodeme (arthropod tendon) could store only a small fraction of the strain energy underlying the work requirements in an average strike, which means that stomatopods need a specialized spring.
In our model for the stomatopod strike, elastic energy is stored in a compressive, saddle-shaped spring that is a stiff exoskeletal structure located dorsally on the merus (the enlarged proximal segment) of all stomatopods. Hyperbolic–paraboloid (saddle-shaped or anticlastic surfaces are used in engineering and architecture: their opposite and transverse curvatures reduce failure by distributing stresses across the three-dimensional surface. Likewise, the saddle shape of the stomatopod’s spring minimizes the probability of local buckling while compressing and extending. To our knowledge, the stomatopod’s saddle is the first biological hyperbolic–paraboloid spring to be described.
Stomatopod smashing produces a loud pop, and high-speed video images reveal evidence of cavitation. Cavitation occurs in fluids when areas of low pressure form vapour bubbles that collapse and yield considerable energy (in the form of heat, light and sound); these can be sufficient to destroy boat propellers and other hard surfaces(7). Cavitation has been noted in snapping shrimp, which appear to ‘shoot’ cavitation bubbles at prey items to stun them(8,9).
By contrast, cavitation in stomatopods occurs between the surface being struck and the dactyl heel. Although the heel is highly mineralized(10), the surface becomes pitted and damaged over time; stomatopods moult frequently and produce a new smashing surface every few months. In addition to their novel energy-storage mechanism and remarkable striking speed, stomatopods may be using cavitation forces to process their prey.
References:
1. Burrows, M. Zeit. Vergl. Physiol. 62, 361–381 (1969).
2. Burrows, M. & Hoyle, G. J. Exp. Zool. 179, 379–394 (1972).
3. Alexander, R. M. & Bennet-Clark, H. C. Nature 265, 114–117 (1977).
4. Bennet-Clark, H. C. in The Insect Integument (ed. Hepburn, H. R.) 421–443 (Elsevier, Amsterdam, 1976).
5. Gronenberg, W. J. Comp. Phys. A 178, 727–734 (1996).
6. Alexander, R. M. Comp. Biochem. Phys. A 133, 1001–1011 (2002).
7. Brennen, C. E. Cavitation and Bubble Dynamics (Oxford University Press, New York, 1995).
8. Lohse, D., Schmitz, B. & Versluis, M. Nature 413, 477–478 (2001).
9. Versluis, M., Schmitz, B., von der Heydt, A. & Lohse, D. Science 289, 2114–2117 (2000).
10. Currey, J. D., Nash, A. & Bonfield, W. J. Mater. Sci. 17, 1939–1944 (1982).
© 2004 Nature PublishingGroup
This shrimp packs a punch powerful enough to smash its prey’s shell underwater.
S. N. Patek, W. L. Korff, R. L. Caldwell
Department of Integrative Biology, University of
California, Berkeley, California 94720-3140, USA
Nature
Vol. 428
April 22, 2004
Stomatopods (mantis shrimp) are well known for the feeding appendages they use to smash shells and impale fish. Here we show that the peacock mantis shrimp (Odontodactylus scyllarus) generates an extremely fast strike that requires major energy storage and release, which we explain in terms of a saddle-shaped exoskeletal spring mechanism. High-speed images reveal the formation and collapse of vapour bubbles next to the prey due to swift movement of the appendage towards it, indi-cating that O. scyllarus may use destructive cavitation forces to damage its prey.
Stomatopod appendages were previously thought to be limited to a maximum speed of 10 m s-1(1) but, by using new imaging technology and a faster species, we have measured the dactyl heel reaching peak speeds of 14–23 m s-1, peak angular speeds of 670–990 rad s-1, and peak acceleration of 65–104 km s-2 within an average period of 2.7 ms, making O. scyllarus perhaps the fastest appendicular striker in the animal kingdom.
To generate these extreme movements in water, a large amount of energy must be released over a short period. Stomatopods increase their power output through the use of a click mechanism, in which latches prevent appendage movement until muscle contraction is maximal(1,2). When the latch is freed, stored energy is released over a shorter time than the duration of the original muscle contraction. Some extreme animal movements also require a specialized spring, because the muscle fibres and tendon store insufficient elastic strain energy(3–5). We conservatively calculate that a minimum power requirement of 4.7 x 10-5 watts per kilogram of muscle is necessary for a typical strike, which is orders of magnitude higher than that available in the fastest-contracting muscles(3,6) known. Moreover, the lateral extensor muscle and apodeme (arthropod tendon) could store only a small fraction of the strain energy underlying the work requirements in an average strike, which means that stomatopods need a specialized spring.
In our model for the stomatopod strike, elastic energy is stored in a compressive, saddle-shaped spring that is a stiff exoskeletal structure located dorsally on the merus (the enlarged proximal segment) of all stomatopods. Hyperbolic–paraboloid (saddle-shaped or anticlastic surfaces are used in engineering and architecture: their opposite and transverse curvatures reduce failure by distributing stresses across the three-dimensional surface. Likewise, the saddle shape of the stomatopod’s spring minimizes the probability of local buckling while compressing and extending. To our knowledge, the stomatopod’s saddle is the first biological hyperbolic–paraboloid spring to be described.
Stomatopod smashing produces a loud pop, and high-speed video images reveal evidence of cavitation. Cavitation occurs in fluids when areas of low pressure form vapour bubbles that collapse and yield considerable energy (in the form of heat, light and sound); these can be sufficient to destroy boat propellers and other hard surfaces(7). Cavitation has been noted in snapping shrimp, which appear to ‘shoot’ cavitation bubbles at prey items to stun them(8,9).
By contrast, cavitation in stomatopods occurs between the surface being struck and the dactyl heel. Although the heel is highly mineralized(10), the surface becomes pitted and damaged over time; stomatopods moult frequently and produce a new smashing surface every few months. In addition to their novel energy-storage mechanism and remarkable striking speed, stomatopods may be using cavitation forces to process their prey.
References:
1. Burrows, M. Zeit. Vergl. Physiol. 62, 361–381 (1969).
2. Burrows, M. & Hoyle, G. J. Exp. Zool. 179, 379–394 (1972).
3. Alexander, R. M. & Bennet-Clark, H. C. Nature 265, 114–117 (1977).
4. Bennet-Clark, H. C. in The Insect Integument (ed. Hepburn, H. R.) 421–443 (Elsevier, Amsterdam, 1976).
5. Gronenberg, W. J. Comp. Phys. A 178, 727–734 (1996).
6. Alexander, R. M. Comp. Biochem. Phys. A 133, 1001–1011 (2002).
7. Brennen, C. E. Cavitation and Bubble Dynamics (Oxford University Press, New York, 1995).
8. Lohse, D., Schmitz, B. & Versluis, M. Nature 413, 477–478 (2001).
9. Versluis, M., Schmitz, B., von der Heydt, A. & Lohse, D. Science 289, 2114–2117 (2000).
10. Currey, J. D., Nash, A. & Bonfield, W. J. Mater. Sci. 17, 1939–1944 (1982).
© 2004 Nature PublishingGroup
