Mantis Shrimp Bio-Armor

Cover shot by Roy Caldwell

There is mantis shrimp double-trouble in this month’s Journal of Experimental Biology, which features not one, but two papers about stomatopods. One, Porter et al., is a new phylogeny of stomatopods, including some eye structure character reconstructions. The second paper, by Taylor and Patek, is a study on stomatopod armor employed in ritualized sparring.

I’ll be writing the phylogeny paper up in detail later this week, so now I will talk briefly about the mantis shrimp’s powerful bio-armor, as reported by Sheila Patek’s lab.

In a previous post, I discussed the ‘super strength’ of the mantis shrimp’s raptorial appendages. In ‘smasher’ mantis shrimp, these specialized biological hammers can be deployed with incredible speed and force, literally vaporizing water around the impact site by cavitation forces. In that previous post, I mentioned that stomatopods primarily use their raptorial appendages for predation, defense, and chiseling out burrows. However, some species also use their battle-hammers for intraspecific competition; sparring matches that decide territorial disputes.

In these sparring matches, two stomatopods exchange blows to each other’s telsons; their shield-like tail segments. The strength of the blows is used to establish dominance without resulting in lethality or serious damage to one, or both, of the animals.

Ritualized sparring amongst smasher mantis shrimp. The left stomatopod parries the attack of the other with its telson, a shield-like terminal body segment. The attack is absorbed by the telson and the left mantis shrimp then flips over to returns the attack. Adapted from Caldwell and Dingle, 1976.

Taylor and Patek wanted to better understand the structural modifications and impact dynamics of the telson that allow for the absorption of such brutal impacts. In order to achieve this they dropped steel balls onto mantis shrimp (Neogonodactylus wennerae) telsons and recorded the impacts with high speed video cameras. They used the impact data to calculate a coefficient of restitution for the telson. The coefficient of restitution is commonly used in tests of automobile collisions, body armor, and protective sporting equipment. It expresses impacts in terms of a ratio between relative velocity after and before impacts. This analysis indicated that the stomatopod telson absorbs impacts inelastically, more like a punching bag than a trampoline.

CT scan of a stomatopod telson. Whiter areas are heavily mineralized and more rigid. From Taylor and Patek, 2010.

The researchers also used CT scanning to look at the structure and mineralization pattern of the stomatopod telson. They found that the exoskeleton cuticle is twice as thick in three ridges, called carina, that run along the telson. These carina do not deform during ballistic impact, but the overall dome of the telson does. The interplay of this mixture of rigid and compliant structures may increase the absorptive capabilities of the telson. Indeed, similar structural strategies are employed in the design of synthetic armor.

So yet again, it seems evolution has beaten human engineers to the punch. Many of the structural, impact-resistant properties found in the stomatopod telson are also utilized in the construction of impact-resistant materials. By further studying the biomechanics of stomatopod ritualized combat, Taylor and Patek hope to better understand the evolution of such interactions and the protective structures they employ. Ideally, this work could impart lessons about the design of protective structures to human engineers. It would be hard to beat hundreds of millions of years of evolutionary product testing.

References:

  • Thank’s to the Patek lab for letting me visit and shine UV lights at their stomatopods when they were still at UC Berkeley. It was interesting to see some of this biomechanical work being preformed.
  • Taylor, J., & Patek, S. (2010). Ritualized fighting and biological armor: the impact mechanics of the mantis shrimp’s telson. Journal of Experimental Biology, 213 (20), 3496-3504 DOI: 10.1242/jeb.047233
  • Caldwell and Dingle (1976) Stomatopods. Sci. Am. 234, 80-89.

7 Comments

  1. Mike Lisieski October 5, 2010 2:08 pm Reply

    Solid post! Looking forward to the one on mantis shrimp phylogeny.

    http://www.cephalove.southernfriedscience.com

  2. Southern Fried Scientist October 5, 2010 6:00 pm Reply

    Damn, I knew mantis shrimp had some punch to them, but didn’t realize they had that much power.

    We did once have a mantis smash through the side of a small aquarium in the middle of invert class.

    The real question is, who would win in a natural-armor-off, stomatopods or scaly footed gastropods

    http://southernfriedscience.com

  3. Michael Bok October 5, 2010 6:24 pm Reply

    The gastropod wouldn’t stand a chance. For one, it has no offense, the best it could do is sit there and take it. The stomatopods would just gradually chip their way through the shell, they could ignore the armored foot.

  4. MJ January 7, 2011 5:28 am Reply

    yeah guys come on. stomatopods all the way.

    http://superrugged.blogspot.com

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