What Are Wood Boring Worms and How Do They Destroy Gulf Coast Docks?

When waterfront property owners call us about dock pilings that are "just falling apart," the cause is almost always the same: marine borers — Teredo shipworms and Limnoria crustaceans — that have been quietly destroying the wood from the inside for years. Understanding how these organisms work is the first step toward protecting your dock from the same fate.

Not Worms at All — But Just as Destructive

Despite the name, "wood boring worms" are not actually worms. Teredo are bivalve mollusks — soft-bodied animals related to clams and oysters — that use a small pair of shells at their head end to drill through wood. Limnoria, often called "gribble," are isopod crustaceans — tiny shrimp-like animals that rasp wood from the surface. Both are marine organisms that require saltwater or brackish water to survive, which is why they are so prevalent throughout the Gulf Coast.

Teredo Shipworms: The Invisible Excavators

Teredo larvae are microscopic when they settle onto a wood surface. They find a crack, a soft spot, or an exposed end grain and drill their way in — leaving behind a pinhole entrance the size of a pencil tip. Once inside, they rotate their shell-tipped heads to excavate a smooth, winding tunnel that follows the wood grain. They line this tunnel with a thin calcium carbonate shell for structural support.

As the Teredo grow, their tunnels widen. Mature specimens can reach two feet or more in length, with tunnel diameters of half an inch or larger. A single piling can house hundreds of individual Teredo, each tunneling independently. The result is a piling that looks structurally sound from the outside while its interior has been reduced to an interconnected maze of galleries — sometimes described as resembling Swiss cheese or a labyrinth.

The damage is structurally devastating because wood's strength depends on its intact cellular structure. When that structure is replaced by air-filled tunnels, the piling loses load-bearing capacity in proportion to the volume of wood removed. A piling that has lost 60% of its interior to Teredo has lost a significant portion of its structural strength — often with no external evidence visible above the waterline.

Limnoria: Surface Erosion Below the Waterline

While Teredo attack from within, Limnoria work from the outside in. These tiny crustaceans — rarely more than 5mm long — rasp wood from the surface, feeding on the cellulose as they go. They work in concentrated colonies, with many individuals feeding on the same area simultaneously. Their feeding creates a characteristic pattern: progressive erosion that narrows a piling's diameter over time, often most severely in the splash zone where tidal action concentrates them.

The "hourglass" piling is a classic Limnoria signature — a piling that is noticeably thinner in the tidal zone than above or below it. This narrowing directly reduces the piling's cross-sectional area and load capacity. When the narrowed section becomes too thin to support the dock load, the piling fails — often suddenly.

Why the Gulf Coast Is So Vulnerable

Both Teredo and Limnoria thrive in warm, saline water — conditions that describe the vast majority of Gulf Coast waterways for most of the year. Water temperatures in the Gulf remain warm for eight or more months annually, and salinity levels in open Gulf waters, tidal inlets, and connected bays are well within the range that supports active borer populations. Even brackish environments like Lake Pontchartrain and the lower Mississippi delta — with salinities well below full seawater — support active Teredo populations during warm months.

The extended warm season in the Gulf South means borer activity is sustained for longer than in northern coastal environments. A piling installed in Maine might survive 20 years before showing significant borer damage. The same piling installed in Slidell or Biloxi might show significant structural compromise in 5–8 years without protection.

The Only Reliable Defense

No paint, stain, preservative, or surface treatment reliably stops established marine borer populations. Creosote-treated pilings, once the standard for Gulf Coast dock construction, resist borers reasonably well when new but lose their effectiveness as the creosote leaches out — a process that accelerates in warm, productive water. Modern pressure-treated lumber performs similarly.

The only approach that provides permanent, reliable protection is physical isolation — enclosing the piling in a barrier that borers physically cannot penetrate. Our patent-pending system combines a fiberglass and polymer wrap with concrete encapsulation to create a sealed environment around the piling. No new borers can establish, and the existing structure is stabilized against further damage from both biological and physical forces.

The sooner protection is applied, the more of the original piling is preserved — and the lower the long-term cost. If your dock pilings have not been inspected in the past few years, a free inspection will tell you exactly where you stand.