In the walls of some old Sussex buildings are blocks of chalk (‘Top Chalk’) from the shore-exposed eroded surface of the Chalk in Sussex, used as cheap infill on the less visible parts of the structure. The blocks are often peppered with holes: larger ones made by piddocks, and smaller ones bored by the marine bristleworm Polydora ciliata. In its larval form or when very young, Polydora invades the shells of oysters and mussels, irritating the molluscs; they respond by secreting repair material that can leave the shell blistered.
Polydora ciliata, my full Latin name,
Affords a respectable aura;
But to oysters and such I’m a troublesome dame,
And they know me as ‘Dora the Borer’.
I’m a polychaete worm with bristly projections,
Which are handy, and help when I’m boring.
My tentacles wave, making menu selections
From my burrow – I don’t go exploring.
I do like to drill in CaCO3,
And to burrow in wood and in clay.
(I practised on oysters who lived in the sea –
I was young then, and wanted to play!)
The holes that I make are distinctively small:
Compared to the piddock’s they’re wee.
Look out for them: next time you see in a wall
A block of Top Chalk, think of me!