Doing the sideways crawl
At low tide, the glistening ooze on the creek-front bustles with activity. Tiny creatures scamper about, flashing spindly legs and a sprinkling of colour if you get close enough.
Instantly familiar by name, sight and demeanour, immortalised as a zodiac sign and a constellation, there is a certain whimsicality and plenty of structural oddities to the crab.
Crabs are part of the mouthwatering prawn, lobster, shrimp and krill clan, crustaceans all, and almost entirely aquatic creatures. Together with insects, spiders and a few other creatures, they constitute the largest animal phylum, Arthropoda. These are creatures with jointed limbs but no backbone. However, crustaceans differ from insects and spiders in having a hardened external skeleton, a calcified hard shell.
Compared to the millionstrong armada of insect species, there are a modest 60,000 or so types of crustacean. About 10% of these are crabs.
From the 3-mm Pea Crab to the Japanese Spider Crab whose legs can span 15 ft, this is a widespread cast of fascinatingly named characters.
Most renowned and dreaded are the crab’s foremost appendages. You may know them as pincers, but they started out as legs, tens of thousands of years ago. In most crab species, they became enlarged and sort of weaponised as the creatures sought dominance of their surroundings.
The other four pairs of legs stuck around, to help it scamper and crawl, creep and dig. They function almost like fingers as they seek out and pick up food in an endless rush. You’ll seldom see the legs at rest above ground.
A crab’s legs can also help you tell land or freshwater from the swimming, marine varieties. In the seafaring fellows, the ends of some legs are modified into flattened oars or paddles. In others, like the Fiddler Crab seen on our creek banks, one pincer in the male is a colourful, swollen claw- like appendage. He waves this, flag-like, to attract mates.
Our creeks and estuaries once teemed with crabs. Marine biologist BF Chhapgar recorded nearly 60 species here in the mid20th century, including several rarities. I doubt if even half this wealth survives today.
Mumbai’s largest crab is the Marsh or Mangrove Crab. As a child I remember sighting specimens in fish markets with shells nearly 10 inches across.
With so many legs, forward movement would have been awkward for crabs. So gracious Nature solved its dilemma by gifting it sideways motion. Indeed, a crab can appear to be moving any which way. Certain ghost crabs can move at as much as 6 kmph. That’s almost as fast as traffic in Mumbai these days!
I wish we were gifted with the any-which-way movement of crabs. It would have been far better than that infamous crab mentality Indians are known for. You must know the joke — you don’t need to put a lid on a barrel of crabs, they say, because if one gets too high, you can count on the others to drag it down.
(Sunjoy Monga is a naturalist, photographer and author of numerous books on biodiversity)