There's simply no hiding it - crabs are among my favourite foods. And of course, I am not alone. Kingfishers, storks, cranes, otters, and a number of wild species eat crabs regularly.
As some of us observed, apparently crabs are fond of crabs too. In this blog I showcase an observation made in the peaceful sacred grove of Kukdeshwar in Udaipur district. With a perennial stream that is protected thanks to the local deity, this spot in the Aravalli mountains is verdant even in the summer heat. Our friend, Dr. Anil Sarsavan - an extraordinary naturalist - showed us the magic of the grove. The wet part was lush, and hopping and buzzing with life.
As we climbed on away from the stream, the dryness was stark, but the beauty of the dry trees alongside the evergreen ones alongside the bright blue sky dappled with clouds was breathtaking.
Ok, back to crabs and our observation. Freshwater crabs in Indian streams and rivers have been poorly studied and even their taxonomy is just being worked out. The large crabs in Udaipur's streams were kindly identified by the taxonomist Dr. Sameer Pati using the photographs I uploaded on the portal inaturalist.org. One of these chunky chaps is apparently the Brown Freshwater Crab Barytelphusa cunicularis. These are fairly common in streams, and venture out on brief sojourns onto the forest floor in search of food.
Their coloration makes them hard to see on the dry leaves in the dim forest light. A startled crab puts on an aggressive display - one that I am always content to watch from afar. Those pincers be stroooong!
The ones in the stream are difficult to spot as well, being similarly coloured as the sand-and-stone of the Aravalli mountains. A hub-bub in one stream caught our eye one morning, and we saw two large crabs feuding. One chap moved faster and had the other chap in his claw moving so rapidly that we barely realized it had happened. Claw crunched through crab-shell in a jiffy. It vanquished literally crumpled.
The victor dragged the unmoving crab to beside a large rock and began feeding. The flowing waters of the stream turned slightly milky - ostensibly from liquids inside the crab being eaten. The "blood" was whitish? The harvested blue blood of the marine horseshoe crabs is famous, but I had no idea that the primary colour of the innard-fluid of a freshwater crab was white.
The victor then crushed the shell completely, and a bright white fluid gushed out colouring the clear, flowing stream. Other crabs did not appear to be attracted to the flowing white stuff, and the meal was had in peace.
We watched mesmerized as claws reached into the broken shell and pulled out succulent white flesh to chew as white fluid continued to pour out and quickly washed away. As the meat was consumed, it took only a few seconds for the water to become clear again leaving no trace of the violence that had just occurred.
There is a considerable amount of research on cannibalism among freshwater crabs, but these studies focus on adult crabs eating freshly hatched or slightly grown young crabs. Given the aquaculture importance of some freshwater crab species, cannibalism is a serious matter for farmers of these species.
Not surprisingly, there appears to be rather little written about cannibalism of adult wild freshwater crabs. In one experimental study, larger freshwater crabs preferred to cannibalize much smaller crabs, males were more cannibalistic than females, and cannibalism disappeared when alternative foods were offered. Crab species have been observed to increase cannibalism during molting when molting crabs display a high degree of agitation making it easy to spot. Aquaculture farmers appear to be familiar with this behavior and routinely provide refuges to reduce cannibalism. Had we observed a molting Barytelphusa cunicularis being cannibalized?
I wonder also if much of the cannibalistic action takes place in the shelter of darkness during the night making it appear that this is rare. Maybe the younger, smaller crabs are just too agile for the biggies to catch, and seem to be able to escape by running away on rocks. Lots of questions, and far too few answers. The way it will always be!
(Photographs taken 30 April 2023. Thanks muchly to Dr. Anil Sarsavan for showing Swati and I the lovely Kukdeshwar sacred grove in Udaipur district.)
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