Digging Like a Clam
The Atlantic razor clam, Ensis directus, has an amazing trick to escape from predators. It’s able to dig into the sand quickly enough to out-dig the fastest digger–going as deep as 70 cm (2.3 ft) in just over a minute. Researchers Amos Winter and A.E. Hosoi at MIT decided to mimic the razor clam to create an efficient, compact burrowing technology that could be used for a lightweight anchor or tether, help install undersea cables, or detonate buried underwater mines. They estimated that RoboClam‘s performance would provide considerable savings of energy and weight over current systems.
According to a 2011 article in Integrative and Comparative Biology, E. directus is distinct for its burrowing performance. The clam has a long a slender set of two valves that rotate relative to each other and a dexterous soft foot at the bottom of the valves. The razor clam burrows by using a series of valve-and-foot motions to draw itself into the substrate. These motions actually fluidize the substrate surrounding its body, essentially turning its tunnel into quicksand, sucking it down and making it easier to dig.
Nearly all bivalves like the razor clam have an elastic ligament that acts as a torsional spring that stores energy during contraction of the valves. This energy can be used later for re-expansion. The resulting energy savings can be substantial. While the energy expenditure measurement of 0.21 J/cm may not mean much to most of us, to put it into perspective, E. directus could travel over half a kilometer through sand on the energy in a AA battery.
Stories like this can add relevance to studies of invertebrates, particularly for students who are familiar with molluscs. The story is also a good example of going from Challenge to Biology, because in this case, the researchers looked across a range of organisms and focused in on the razor clam because it met their needs: efficiency, size, speed, simplicity, and depth of digging. The paper is worth obtaining for the story it tells about the biomimetic process.