Breaking News: Mantis Shrimps Making an Impact

By: Abby Wickie

Despite their small size and often colourful appearance, the mantis shrimp is one of the fiercest and deadliest predators in the ocean. Their secret weapon? Specialized feeding appendages that can deliver one of the strongest and quickest punches in the animal kingdom. The mantis shrimp’s appendages, whether shaped like a blunt club or a sharp spear, can move at a speed of 100,000 m/s and exert a force 2500 times greater than the weight of its own body when hunting prey. In order to deliver such a powerful blow, the mantis shrimp needs an appendage that can endure repeated crushing forces without fracturing. In a study led by Lessa Kay Grunenfelder from the University of California, a team of researchers investigate how the mantis shrimp can inflict such significant damage while remaining unharmed.

Mantis shrimp are divided into two distinct groups: “smashers” that have blunt clubs to break hard-shelled crustaceans, and “spearers” that have sharp spears to slash and impale softer-bodied prey. The spearers evolved first, researchers think, likely as a response to the appearance of hard-shelled prey that a spear couldn’t penetrate. To expand upon past research of the structural components of these appendages, Grunenfelder and her team focused on investigating the complex microstructures in the striated muscle fibres located around the circumference of the club. Using both optical and electron microscopy, the researchers analyzed cross-sections of a smasher and spearer, respectively: the peacock mantis shrimp (Odontodactylus scyllarus) and the zebra mantis shrimp (Lysiosquillina maculata).

The researchers discovered that this striated region within the smasher’s club contains tightly packed sheets of mineralized chitin, while the surrounding areas have organic compounds. This strengthened chitin envelopes the entire appendage, much like how boxers wrap their hands with cloth to form a tight fist and prevent injury upon impact. The team also found that this striated region contains a system of pore channels that enable ion transport and could potentially allow for self-repair following particularly severe impacts.

The team was surprised to discover that a similar striated region existed in the spearer appendages, considering that this species experiences different forces during a feeding strike on soft-bodied prey. They found that the fibers in the spear are arranged in a manner more suitable for longer appendages, which may help minimize deformation when striking prey. The fact that the spearers evolved before the appearance of the smashers suggests that this microstructural feature could have played a significant role in the evolution of the first club-wielding mantis shrimps, as a response to the emergence of hard-shelled crustaceans. On top of this, yet another similar striated structure was identified in the limbs of a praying mantis, indicating that terrestrial arthropods may have independently evolved similar structures for hunting too.

The impact-absorbing structure of these weaponized appendages offer endless possibilities for real-world applications from enhancing aircraft aerofoilds to creating more effective bicycle helmets and golf clubs. Grunenfelder and her team aim to utilize their findings to develop new materials that improve durability and optimize speed and strength, while maintaining structural safety. Slasher or smasher, these mantis shrimps are knockouts that are leaving their mark in their marine ecosystem as well as in the field of science.

References Grunenfelder, L. K., Milliron. G., Herrera, S., Gallana, I., Yaraghi, N., Hughes, N., Evans-Lutterodt, K., Zavattieri, P., Kisailus, D. (2018). Ecologically driven ultrastructural and hydrodynamic designs in stomatopod cuticles. Advanced Materials. 30(9), 1705295.