The uca lacteal, or milky fiddler crab, inhabits mudflats near the river mouth.
The males have a grossly oversized claw that is conspicuously swung back and forth.
This behavior, known as waving, is thought to be a form of courtship, with collective waving actually limited to the breeding season between June and August.
Waving as a group allows the females to see which males can wave their claw the fastest.
The speed with which they wave is an indication of their physical strength.
So, the faster the wave, the more attractive they are to females.
While this group-based behavior makes perfect sense for choosing a mate, why is it then that these crabs wave their claw individually outside of the breeding season?
The milky fiddler crab is usually found inhabiting mudflats around the mouths of large rivers.
River mouth mudflats are home to a wide variety of living organisms.
Along with other sand crabs belonging to the same family as the milky fiddler crab, areas suited to reed grass also attract a rich variety of fish such as gobies.
Sandpipers, plovers and many other birds converge on the mudflats to feed as well.
Of particular note is the whimbrel, a species known to forgo its normal migratory behavior and stay in healthy populated river mouth mudflats over summer to take advantage of easy access to a bountiful supply of food.
Crabs have, of course, developed ways of protecting themselves from such birds.
Crabs belonging to the ocypodidae family generally have periscope-like eyes that they stick out to make sure the surrounding area is safe before emerging.
They are also quick to dash back into their hole at the first sign of danger.
It’s not known just how well sand crabs and milky fiddler crabs can see, but they are definitely sensitive to changes in brightness.
Curiously, the dotillid crab ilyoplax pusilla exhibits behavior reminiscent of waving.
Unlike the courtship displays of milky fiddler crabs, the rhythmic up and down movement displayed by both males and females is believed to facilitate a change in their line of sight in order to better spot predators.
When compared with the behavior of this related species, the high-speed waving of milky fiddler crabs may have originally had a kind of shutter effect aimed at spotting fast moving objects.
There is still a lot we don’t know about the vision of crustaceans.
Recent research has uncovered the existence of species with the ability to detect polarized light, and even those with a sensitivity to specific wavelengths.
The milky fiddler crab may well have developed unique visual sensors after spending many years adapting to life on the mudflats.
Humans do not have such refined sensors with which to measure the natural world.
However, humankind posses the power of analysis, one that goes beyond our natural limitations.
The protection of this diverse and beautiful earth through the analysis of nature is a mission that has been entrusted to humankind.