In water, marching barnacles are indistinguishable from ordinary barnacles. Like any barnacles, they accumulate on stones in the water and the hulls of ships, and are difficult to remove. What makes marching barnacles distinct is that they are mobile.
Once attached to an object, a marching barnacles will wave its tiny, feathery legs about constantly, catching tiny particles to eat. These tiny legs are surprisingly strong given the barnacles’ size. When a large number of marching barnacles accumulate, they act as one organism, moving their legs in a single direction. The motion the barnacles cause can be enough to propel a vessel or stone, albeit only very slightly. Strangely, the barnacles consistently move objects eastward.
This frequent movement apparently strengthens the barnacles’ legs, and when on the sea floor or shore, mature barnacles can literally crawl. This has led to a various unusual occurances. Ships covered in marching barnacles may actually move out of the water when docked, and will continue marching until they dry out and die. Stones and ancient shipwrecks are also known to rise out of the water and march inland, sometimes for miles before coming to a rest. Such an incident is recorded by the historian Thyras:
In that time, Rescara was a prosperous and busy port, frequented by ships of all types. The bay of Rescara was reknowned for its cleanliness. During the war, however, the bay fell into disrepair and pollution, causing myriad undesirable fauna to spawn. It was, however, these fauna that would save the city. As the Harpani barbarians entered the besieged city, the ancient watch tower of King Phaestares - which had long ago been lost in the Floods - rose from the water and onto the land. The Harpani feared it was their sea god bringing wrath for their sins, and they fled far off to never return. The tower eventually tipped and fell. On examination, barnacles with thick and strong tentacles were found on its underside, which the sailors immidiately identified as ‘marching barnacles.’ Seeing that it was these normally troublesome creatures that aided Rescara in its time of need, the Assembly passed legislation that forbade all to kill the barnacles in the Rescara port. The law still stands.
-Historian Thyras, Cities of the Republic
Sailors consider marching barnacles an annoyance and will remove them whenever at port. Seeing a ship slowly lurch out of the water at port is a clear sign of a green captain.
Not a few sailors swear by marching barnacles, saying they aid in both navigation and sailing. If ever lost at sea, one can observe marching barnacles to gain direction, as they consistently move eastward. Treasure hunters have been known to raise the barnacles in small boxes filled with water. If a treasure is found beneath the waves that is too heavy to bring up, the box can be placed beneath or near the treasure and opened slightly. The barnacle larvae hopefully attach themselves to the treasure and, after a few months, the treasure will become mobile, allowing treasure hunters to follow it to a better location.
Some sailors swear that they can control marching barnacles and allow their ships to move swiftly in the water. While most sailors dismiss this as fantasy, it has been suggested this is a plausible phenomena. The famous inventor Hyrfidel created a series of magnets on swinging wooden arms. The contraption, he claimed, would be attached to a mainmast and the magnets moved about to control the direction the barnacles swim. He hypothesized that the barnacles always swim eastward just as a compass always points northward. If a compass could be affected by magnets, why not barnacles. The contraption, however, was not particularly popular and is largely considered a failure.