Squeeze play: brobdingnagian earthmoving "worms" dig their tunnels with a hydraulic ram

Borrowing technology from heart surgeons, O'Reilly and his colleagues, David Carrier of the University of Utah in Salt Lake City and Dale Ritter at Brown University in Providence, Rhode Island, implanted miniature pressure gauges, smaller than a grain of rice, into the body cavities of several caecilians. The pressure peaked, they discovered, at the same time as the forward force did, confirming their hydrostatic-motion hypothesis. Thus what a caecilian does while burrowing is more like driving a steam piston into the ground than pounding a tent stake. Furthermore, when the animal was prevented from sealing its single lung--thus preventing the pressure of the muscles from being transmitted throughout the rest of the body--the caecilian's burrowing force dropped considerably.

Biomechanists have known for some time that the earthworm (a caecilian's favorite meal) also advances by pressurizing its body and squeezing its head forward. So there is a certain symmetry to this story: the only known vertebrate to move by hydrostatic locomotion happens to prey on an invertebrate that relies on the same mechanism. What would it feel like to bait a hook with one of these animals, and reel in a fifty-pound largemouth?

Adam Summers (asummers@uci.edu) is an assistant professor of ecology and evolutionary biology at the University of California, Irvine.

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