What is the pile plague?
The pile plague (Dutch: palenpest) is the name for the mass infestation of timber piles in dikes, locks and harbour works by the shipworm (Teredo navalis), which came to light in the Netherlands from 1730 onwards. Despite the name, the shipworm is not a worm but a boring mollusc with an elongated body that tunnels through submerged timber.
What happened
In 1730, dike inspectors discovered that the timber pile cladding of the dikes along the Zuiderzee and in Zeeland had been hollowed out from within. From outside the wood looked sound; inside it was riddled with tunnels. Sea defences had to be repaired urgently on a very large scale.
Characteristics of the shipworm:
- It lives in salt and brackish water and only attacks permanently submerged timber.
- It bores with the small shell valves at its head; the tunnel is lined internally with calcium carbonate.
- The entry hole stays tiny, which is why the damage is almost invisible from outside.
The consequences for construction
The pile plague forced a structural shift in Dutch hydraulic engineering:
- From timber to stone. Pile claddings were replaced by stone revetments on a bed of fascines and rubble — later the familiar basalt columns. This was far more expensive and led to higher dike levies and local resistance.
- A rethink of material choice. Where timber stayed in salt water, harder species were used, or protective sheathing (copper, later tar and creosote treatment), or the structure was kept above water.
Why it still matters
The shipworm has not gone away. Timber dolphins, jetties, lock gates and sheet piles in salt and brackish water remain genuinely at risk. Key lessons:
- Do not judge timber in salt or brackish water by its appearance; internal attack requires core samples or ultrasonic testing.
- Salinisation or freshening of a water body changes the risk: where salt water intrudes, a previously safe timber structure can suddenly become vulnerable.
- In fresh water the shipworm plays no role; there, fungi and bacteria are the decisive agents of decay.
Related terms
- Pile dike
- Pile rot
- Sheet piling
- Driven pile
- Dike
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