On his 4th voyage over to America, Christopher Columbus lost all of his ships to shipworms. All of them. Why was so little wood found on the sunken Titanic when they finally raised it from the ocean floor? You got it…shipworms. You got that right, right?

Mollusks, Actually

So what are shipworms…and why and how do they cause so much damage? Shipworms (also known as Pileworms) actually are not really worms at all, but are rather a type of clam that has very small shells used for boring into wood in saltwater.

A marine bivalve mollusk (with 65 different species)…they get their name for their long, narrow, cylindrical bodies – resembling worms. However, upon closer inspection, you will find a small drill-like shell. This shell has two halves with a gap between them, like a clamshell. In the gap there is a muscular foot that acts as a suction cup, holding the shell in place while it’s razor-sharp edges scrape the wood ahead of it. Shipworms have long tubes that stick out into the water so the worm can breathe, and can also seal the worm in the wood in cases of extended periods out of water…low tides for example.

Up To 6 Feet Long

Also known as “Termites of the sea”, shipworms eat sawdust. The stomach of shipworms has a pouch for storing sawdust and an organ/gland full of bacteria that aide in digesting wood. The bacteria take nitrogen from the water and convert it to protein for the worms’ nourishment. The shipworm invades wood while still in the larval stage, making an entrance hall that is usually too small to see. It uses the shells on its head to burrow. The ridged, rough surfaces rub the wood away as the worm moves from side to side. This cuts away a perfectly circular tube that is just larger than the shell. The wormlike body follows behind the shell, producing a chalk-like substance to line the burrow. As they burrow deeply into the wood, they grow very quickly. As the worm grows, so does the burrow. Depending on the size of their homes, shipworms can range in size from 6 inches to as long as 6 feet.

Expensive Damages

Once a shipworm claims a home, it is there for life. A piece of wood may be infested with shipworm, but they will deliberately avoid each other’s tunnels. Instead they twist and turn their tunnels until the wood becomes a mass of tubes and holes, and eventually collapses. Shipworms are sometimes called the mollusk with the million-dollar appetite. These creatures are credited with single-handedly destroying the Hudson River piers in New York City. Researchers estimate that untreated timbers, such as pier pilings, exposed to Hawaii’s ocean waters will last less than two years.

A Positive Note

However, this incredible appetite has a purpose. Large amounts of wood get into the oceans by river deposits, forests and mostly, humans. Shipworms play an integral role in reducing the amount of driftwood in the world’s oceans.

How To Stop Shipworms

So, how do we stop the shipworms & protect our ships & wooden structures? By protesting at the White House? Not likely. Shipworms don’t like copper….so we can build using copper nails, or even copper sheeting. A cheaper and easier method is simply using CCA treated wood which contains copper (CCA = Chromated COPPER Arsenate).

Well, We Like Oysters

Or, we can eat them. In some places, shipworms are considered a culinary delicacy. In the Philippines, it is prepared as ‘kinilaw’ – eaten raw, with vinegar or lime juice & chopped peppers and onions…Similar to ceviche. The taste has been compared to a very wide variety of foods ranging from milk to oysters.

Here are some options for those of you perplexed by the question of how to preserve wood posts. Whether you are trying to build a long-lasting fence or other structure or trying to extend the life of existing wood posts you have options. Without exceptions, the options are far easier before installation.

Pressure Treated Wood Posts
No additional work required – just buy wood posts treated for ground contact (usually .40pcf). Depending on the area where you are installing your pressure treated wood posts, they should last between 10 and 30 years (maybe more). 10 years if the area is pretty wet and/or has a bad termite problem and 30 years if the area is pretty dry.

Poly Coated Treated Wood Posts
I only know of one place that offers poly coated wood posts – American Pole and Timber based in Houston, TX. The coating is a UV-resistant “poly urea” coating (look and feels like heavy vinyl) and is obviously tough as hell and will not come off of the wood. They guarantee treated poly coated posts will last 50 years. Pretty impressive. The product has only been around for about 10 years but I would put money on 50 years for treated wood coated with a thick UV-resistant vinyl. They supply any quantity but if you are outside of Texas or Louisiana, you might need to buy quite a few to justify the freight expense. You only need to have the post coated from about 6 inches above the ground line to the bottom of the post.

Plastic Coated Wood Posts
Similar to poly coated wood but I wouldn’t put my money on it. Buy treated posts and spray the bottom of the post up to about 6 inches above the ground line with spray-on plastic in a can. You can get a can of spray-on plastic for about $5 at the major big-box hardware stores. One can should easily cover the bottom 3 feet of about 10 posts. It’s cheaper than the vinyl option and should add 10 years onto any posts life.

Sealants or Stains
If you are going to seal or stain pressure treated wood, make sure it is dry first since sealing in the moisture left from the treating process will only make your posts rot faster. Sealing untreated posts will add a few years to their lives but, seriously, just get treated posts – unless you just LIKE replacing fences.

Paint
Paint is for color – not protection. Yes, it protects a little but, again, if you are going to use paint to preserve untreated wood posts just go ahead and admit that you like replacing fence posts. Want color? Paint away. Want preservation? Use treated posts.

The BEST WAY to Preserve Wood Posts
In my opinion, the absolute BEST way to preserve wood posts is with pressure treatment – whichever treatment chemical you choose – and a coating of some kind. The longest lasting wood posts will be pressure treated and coated with the vinyl coating. The most bang for your buck will probably be to use pressure treated posts and spray-on plastic.

Now you know how to preserve wood posts and which methods will work best for you. If you choose paint, don’t call me because I hate replacing posts. I will gladly lay in my hammock – supported by my vinyl coated treated posts – while you install your second set of painted posts, though.