Mud Crab Food

At the mouth of the Richters Creek (Cairns), shells are balanced on the mangrove prop roots.  What is this all about?

Mud-creeper shells in a tree

Many of the shells are severely damaged and this is a clue.  There is only one animal that can follow the spiral, crushing away solid shell - the mud crab.

Mud crab damaged Telescopium shell

Hermit crabs appear to be the main prey although according to the scientific literature mud crabs can prey on the Telescopium and Terebralia mud-creeper snails as well.  After the mud crab has eaten the shell's current inhabitant, an new inhabitant often moves in.  A full sized shell may be reduced in stages down to small remnant as inhabitant after inhabitant is eaten.  It is no wonder hermit crabs have learned to climb trees.

A hermit crab