Gribbles are destroying Seattle's seawall. And it's serious. So serious, in fact, that the Seattle City Council on Monday unanimously voted to stick a $290 million bond on the Nov. 6 ballot, designed to rebuild the seawall and two city-owned piers. All of this, of course, raises the question: What the hell is a gribble?
First, a bit of the wormy context: On Tuesday, following the City Council's vote, the Seattle Times reported that engineers say Seattle's seawall has been "badly eroded by gribbles and bore worms, and could collapse in a major earthquake or storm, causing widespread damage to property along the waterfront."
Sounds scary, right? And it is. But Dr. Megan Dethier, a research professor who studies marine intertidal ecology at the University of Washington Friday Harbor Laboratories, says gribbles, despite the dangers they pose to wood, are actually "amusing critters." An isopod crustacean from the family Limnoriidae with roughly 56 different species, the gribbles wreaking havoc on Seattle's seawall eat wood in and around ocean water. Dethier says there are three species of gribble locally, and the wood-devouring creatures are likely "very prevalent."
Remote relatives of shrimp and crabs, Dethier points out gribbles are also related to run-of-the-mill pill bugs, roly-polies or potato bugs found under rocks in your yard. Typically measuring only a few millimeters, gribbles are the creatures responsible for the burrowed holes found in most pieces of driftwood. They live at the edge of water, on floating wood, or along the sea floor, devouring whatever they can.
"They can basically make [wood in or near the water] crumble," says Dethier. She estimates the time it would take gribbles to devour an untreated piling or pier as "years, not decades."
Scared yet? You should be. Freakier still, Dethier says gribbles can't be stopped all together. They can, however, be slowed down by wood-preserving agents like creosote. Or engineers can just use a material like concrete. Despite their ferocious powers, Dethier reports gribbles can't eat concrete.
"The bottom line is gribbles are serious pests," says Dethier, "especially for old wood."