A pile of limestone boulders lies along the seawall behind our condominium complex, presumably placed to reinforce the wall and to protect the entrance to our boat canal. Over the years, these rocks have become a reef within the bay, attracting a wide variety of marine life, from silverlings to dolphins. Above the waterline, the boulders are also home to a large colony of marine centipedes; hiding among the crevices during the heat of the day, they scurry about in the early morning and evening hours, potential snacks for herons that also stalk this site.
Centipedes, close relatives of shrimp and crayfish, are primarily carnivorous, feeding on a variety of small animal life. Those that inhabit our rock pile forage at the waterline, feeding on small barnacles and on other creatures that either feed on the algae or are swept in with the flotsam. Occasionally threatened by incoming waves, they, like sandpipers, are adept at outrunning the surf; of course, their flat body form and numerous legs help to insure that they won't be swept into the bay.
Invertebrates such as these centipedes are thought to have been the first animals to colonize the land, having come ashore during the Silurian Period, about 420 million years ago. Facing a barren, rocky landscape, they initially stayed near the coast where pioneer plants provided cover and where food was delivered by the waves and tides; over the eons, through the processes of evolution and natural selection, these invertebrates gave rise to all other terrestrial animals, including humans. Staring at the centipedes on our seawall reef, I could be looking at a scene from the Silurian.
