The Incredible Coconut Crab

The Coconut Crab, Birgus latro, is the largest terrestrial arthropod in the world and has a pinching power 90 times its own body weight. Its claws exert 10 times as much force as a human hand.

But today we are looking at the microscopic make-up of its shell.

People who live alongside Coconut Crabs have been aware for a long time about the strength of these animal’s shells and how difficult it is to eat them.

This amazing strength combined with the relative lightness of the crab’s shell encouraged a study by the NIMS Research Center for Structural Materials.

By dissecting and examining a segment of the crab’s shell they found incredibly complex structures. Researchers used super high-tech processing machines called things like ‘Xe-plasma type FIB-SEM (Thermo Fisher Scientific Helios PFIB G4 UX)’

This allowed them to identify three distinct layers of a Coconut crab’s shell - a thin but hard outer layer called the exocuticle, a much thicker but softer layer below called the endocuticle and an inner membrane.

The scientists suggest that the two outer layers work together to provide maximum protection for the crab.

The outer exocuticle layer is made up of approximately 100 microscopic plates which gradually twist horizontally. The layer resembles a twisted plywood-like structure and is as hard as steel.

Combined with this, the softer endocuticle works to absorb pressure which helps protect the outer shell.

It is the first time that these techniques from the material sciences have been used to closely examine the make-up of an animal’s exoskeleton.

PC: Elsevier - Three-dimensional microstructure of robust claw of coconut crab, one of the largest terrestrial crustaceans, Inoue, Oka, Hara, 2021