What are these small creatures popping in and out from their burrows vigilantly on the sandflat and mudflat? They are like children playing hide-and-seek! These cute tiny creatures are fiddler crabs, a kind of intertidal crabs.
On Lantau, four fiddler crab species are commonly seen, they are the Bowed Fiddler Crab (Tubuca arcuate), Splendid Fiddler Crab (Paraleptuca crassipes), Milky Fiddler Crab (Austruca lactea) and Northern Calling Fiddler Crab (Gelasimus borealis). Among them, the most conspicuous one is the Splendid Fiddler Crab, for its black and turquoise striped shell and its orange red claws and legs, resembling a watermelon!
One can easily discern the gender of a fiddler crab by looking at its claws. Females have a pair of relatively small, evenly sized claws, both of which are used in feeding. On the other hand, males have a pair of unequally sized claws, with an enlarged one for self-defense, fighting and attracting females, and the other serving for feeding. During the mating season, male fiddler crabs will show off their power by waving around their enlarged claw, in a bid to attract females and to repel intruders or competitors from their turf.
Fiddler crabs are distinctively unique in their feeding behaviour. They scrap sediments up to mouthparts with their feeding claws, which act as filters to sift out the organic food matters they need. Any residue sediments are then discarded near their burrows in the form of small sand pellets. Therefore, many scattered sand pellets you may see on the sandflat and mudflat during low tide might be their food waste! When the male crabs are feeding, they are like playing a violin with their claws, so that is why they are called fiddler crabs!
Given both male and female fiddler crabs share the same feeding habit, the females are supposedly larger in size as they have a pair of feeding claws. The facts tell the exact opposite story, for the males are larger in size. But why? Is their bigger size a manifestation of the greater strength to protect their families, just as a strong and muscular body may give an impression of fierceness and being a good fighter? Come and visit Shui Hau, Tung Chung and Tai O at your leisure for the answer. But watch out. Please do not disturb them while they are enjoying their meals or dating.