Finger-width holes on tidal mudflats are the handiwork of the tunnelling mud crab (Helice crassa), and you might see these tiny grey-green crabs scuttling back into their tunnels if you pass too closely by these nervous creatures. They have reason to be nervous, they’re food for wading birds, gulls, kingfishers, fish… it’s a long list. The tunnels serve as protection from predators and also aid in stopping the crabs from drying out. During the day when the tide is out, they scurry around eating tiny things that live in the mud. At night and when the tide is in, the safest place is in a tunnel, which they might block up to keep predators out. Thinking of digging into a tunnel to go after a crab that’s disappeared into it? Probably not a great idea as the tunnels can be complex, with multiple entrances; the crab is probably long gone. If cornered, they’ll assume a defensive posture, as in this photo. (No tunnelling mud crabs were harmed in the taking of this photo. Except perhaps psychologically.)
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