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How Marine Borers Destroy Wood

Shipworms (Teredos) and Gribbles (Limnoria)

Shipworms and Gribbles are the main causes of organic damage to marine structures. The best solution for protection against marine borers is to protect the wood with a physical barrier which does not allow marine borers to reach or penetrate the wood.

Shipworms (Teredos)

Shipworms live in saltwater or brackish water and can get up to SIX FEET LONG. They are worm-like bivalve mollusks with a greatly reduced shell which they use to bore tunnels into wood. Shipworms typically spend their entire lives in a tunnel in a single piece of wood.

Shipworms damage the wood from the inside-out. The damage is difficult to assess but you can recognize a shipworm infestation by the small holes they leave in the wood.

"Wherever you have untreated timber, you're going to have problems with shipworms," said David M. Cacoilo, a partner and design engineer at Mueser Rutledge Consulting Engineers in New York, which has worked on a dozen marine borer projects. "Once they're there, the potential for the population to explode is tremendous."

Gribbles (Limnoria)

Gribbles attack in huge numbers at the outer edges of the wood and create the common “hour-glass” shape pilings often develop at water level.

Gribbles are nearly microscopic crustaceans, resembling the wood louse, with seven pairs of legs and four pairs of mouthparts. Given enough time, they can devour the pilings under a pier until the structure is weakened enough to collapse.

Clean Water Equals More Marine Borers

Interestingly, a large population of shipworms and gribbles indicates low water pollution levels. Areas with high levels of pollution in the water have little problems with these marine borers but when the water gets cleaned up, they move in.

Ultimate Solution to Marine Borer Attack

American Pole and Timber suggests using CCA pressure treated poles, pilings, and timbers and coating them with 21 POLY vinyl coating as the ultimate solution for protecting wood structures against marine borer attacks.

21 POLY is a vinyl coating specially engineered to bond to wood. It is approved, and used, by the corps of engineers and is proven effective at protecting wood structures against marine borers. For more information about 21 POLY, go to

Call American Pole and Timber toll free at (866) 397-3038 to ask about 21 POLY Coated timbers, poles, pilings, and lumber.

New Website with New SUPER ULTRA CONTENT

The new and improved and super-ultra-amazing Pole and Timber website will be out in late August or early September! Check back often at In addition to more interactive content, it will include cut sheets for our products and information specification sheets for treated wood and marine construction.

Until Next Week

Good luck out there and call us if you need anything!

American Pole and Timber is a national manufacturer and supplier of treated poles, timbers, pilings, large timber trusses, and other commercial and industrial wood products. Call us at (866) 397-3038 or contact us online.

- Article by Chris Denny