Meet the Marsh Engineers
If you’ve ever walked along a tidal creek and noticed clusters of tiny holes dotting the mud, you’ve stumbled onto a whole neighborhood of fiddler crabs at work.
These photos of burrows were captured in Rumney Marsh during low tide on the morning of October 19th, 2025. For a closer look at these crabs in Rumney Marsh, check out Greg Cook’s amazing photo series on his site: https://gregcookland.com/wonderland/2021/09/03/rumney-marsh/
Rumney Marsh, October 19th, 2025 by Rumney Marsh Conservancy
Fiddler Crab Activity
Who’s making them: Fiddler crabs live in the intertidal mudflats and upper creek banks of salt marshes. Each crab excavates its own burrow, often ½ to 1 inch in diameter and several inches deep.
Purpose: These burrows provide shelter from predators, temperature extremes, and drying out during low tide. Males also use them for courtship displays, where that oversized claw comes into play.
Ecological role: Their digging helps aerate the soil, drain surface water, and recycle nutrients. By mixing oxygen into deeper sediments, they improve conditions for saltmarsh plants like Spartina alterniflora.
How to Recognize Them
Clusters of round holes appear just above or alongside a tidal creek or panne edge.
Small pellets of rolled mud are often scattered nearby from feeding activity.
They are most common where vegetation thins and the ground transitions from firm grass roots to softer mud.
Why It Matters for Rumney Marsh
The presence of fiddler crabs is a good sign for Rumney Marsh. It shows that sections of the marsh still have healthy tidal exchange, soft mudflats, and oxygenated soils that can support these sensitive crustaceans. Their burrowing activity keeps the sediment loose and breathable, which helps the marsh absorb and release water more naturally after tides and storms.
As Rumney Marsh continues to recover from decades of filling and pollution, the return and spread of fiddler crabs can be seen as a small but meaningful indicator that the ecosystem is stabilizing and functioning again.
