Crab cannibalism

 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.)

Beetles with spines

 The diversity of form and shapes of beetles are perhaps unparalleled in the animal kingdom. There was clearly an inordinate need for this variety, and I am growing rather fond of discovering more of these. This blog shows a few that I found in the Vaccine Depot Ground of Belgaum city.

The Vaccine Depot Ground in Belgaum city, south India seems like just another green urban space, but a closer look helps reveal it to be a magnificent remnant old forest. The human touch, however, is everywhere - buildings, rows of one tree species, a block filled with an exotic tree, invaluable open grasslands being destroyed by feel-goody tree plantings, and of course a growing network of paved paths. For the burgeoning Belgaum city, the depot's greenness provides critical functions of being both a vital lung and giving people a peaceful natural experience during their morning walks. 

A large manner of wild species use the depot and one group that has caught my attention is rather wacky. These are beetles with spines. Not vertebrae, of course, but actual sharp, long, curved and varied spines. Entomologists know of these and plenty has been written about their taxonomy, role in ecology, and so on. Quite a few different kinds of spiny beetles occur, and here are a few from Vaccine Depot. Here, I share my amazement at the crazy-coolness of a few beetles I found at the Vaccine Depot Ground.

The first one I saw was a weevil, Hoplapoderus gemmatus, that was tiny but packed a punch in appearance. This species belongs to a group broadly named as the leaf-rolling beetles, or Attelabidae. Seen from above, the beetle is good looking already sporting an exotic gold-and-black appearance.

The spines, however, pop when this fella is viewed slightly from the side. Spines of this beetle are somewhat gentle, as if included as an afterthought. And they add, I thought, quite a surprising attractive complexity to the look. 

A much tinier, but far spinier, beetle I saw was Hispa ramosa. This chap was about as thick as a grass blade and looked more like a tiny caterpillar thanks to the densely covered spines. Hispa belongs to a group of beetles called "leaf beetles" - a group that has quite a few species whose larvae feed on leaves of both wild plants and on domestic crops. 

The bizarreness and fabulousness of the spikiness went up a few notches with two Tortoise and Hispine Beetles. One that I have not yet been able to identify to genus or species level is this gorgeous chap sporting a row of two-pronged gold-and-black spikes on its thorax. These were completely overshadowed by the forest of black curved spines on its wings! Look closely and you can see a row of golden spikes jutting out from its sides.

Hate it or love it, the chap is arresting. Add the velvety looking flat feet at the end of the yellow legs, and we have a certified looker in our hands.

   Then came this astounding spined beetle that managed to beat our looker above - Platypria, another leaf beetle. It was by accident that I found this beetle. It was in the web of a social spider quite dead but affording a great opportunity to take photographs from all sides. Four species of this genus are known from India, and going by the photographs of all the species, I would venture to guess that I had found P. echidna.

There were multi-colour spines everywhere on this beetle. And in all sorts of shapes. I assume that the generic name alludes to its overall shape somewhat resembling a Platypus. While the back had several simple spines, the sides were awash with spine diversity. Six-pronged ones, three-pronged ones, coloured ones, semi-transparent ones - you name it, he had it! Add the lush golden-yellow legs and I had meself an unbelievable beetle!

Spines and spikes on beetles have attracted some research attention, and are known to reduce predation. Not only are these spined beetles avoided by birds and frogs and lizards, but also by parasitic wasps. The spines clearly lost their use when caught in a web. It would have been really great to watch the spiders and see how they avoided all of those spines. Perhaps I will get lucky another time.

(Photographs were taken in the Vaccine Depot Grounds of Belgaum, Karnataka during May 2024.)

A predator becomes prey

 Spiders are deadly predators. They use a variety of methods to catch their prey. The ones sitting on their webs waiting for something to be caught in the sticky web are the most well known. This gigantic Nephila pilipes, or the Northern Golden Orb Weaver is one such sit-and-wait species that builds large webs. Other species and tiny males of the species are parasitic on the webs of the large females, eating up prey that the female bundles up in a web and stores for future feeding.

Also a sit-and-wait predator, this Hersilia, or the Two-tail Spider, dispenses with building a web. It is superbly well camouflaged on the bark of trees where it waits for prey sitting upside-down. As an insect or another prey wanders by, the spider spins a web around it by running round and round the prey until it is unable to move. The spider then, as seen in the photo below, moves in and bites the prey injecting it with a poison that incapacitates it. The poison also dissolves the innards of the prey allowing the spider to suck out the juices at leisure.

Then there are the wandering spiders that roam around looking for prey, like this handsome Plexippus paykulli, also called the Pantropical Jumping Spider - a species commonly seen in gardens and homes.  

One sit-and-wait spider that is incredibly attractive is the group collectively called the Crab Spiders because of their overall appearance. These spiders come in a variety of colours matching flowers on which they sit awaiting insects that come for nectary and pollen. Several of these Crab Spiders lived on the Rangoon Creeper vine-gone-wild Swati and I grew in our tiny garden in Udaipur. 

One evening, we noticed struggling movement on one of the buds. It was a black-and-white hoverfly that appeared to be floating in the bunch of flowers. Hoverflies are also called Flower Flies and adults feed on nectar and pollen of flowers. A ghostly form skulked behind the struggling fly. It was a lovely white-and-pink Crab Spider that had successfully caught itself a large meal.

The spider was surprisingly small given the size of the hoverfly it had grabbed and vanquished. The struggling of the fly died down and the spider proceeded to bite into its belly and began feeding. After several minutes, we watched the limp and empty body of the hoverfly drop from the flowers as the Crab Spider let go after having its fill. The spider then proceeded to clean itself before again positioning itself below a new flower.

 
We had barely begun admiring the Crab Spider's skills when there was a very rapid jumping movement towards the Crab Spider. Before it could move, it was in the jaws of a new predator that had been quietly roaming around, perhaps even watching the drama that had unfolded. The new predator was a species of jumping spider quite royally named Thyene imperialis.

Despite being smaller than the Crab Spider, the bite of the Thyene imperialis appeared to have an almost instant effect. The Crab Spider appeared to crumple and was taken around quite effortlessly by the new predator. Thyene positioned itself to get away from our prying eyes and even dangled the Crab Spider over leaves as it jumped away with its fresh food. 

Thyene imperialis is reputed to be a very effective predator, even jumping into webs to grab spiders waiting for prey. The Crab Spider really had no chance once it had been spotted. Even the most well camouflaged and careful of predators can become prey in a trice.

The variety of spider species and behaviours is rather vast. I have no doubt that there will be other blog posts on these eight-legged wonders.

(Photographs' location and dates:

Nephila pinipes: 12 Jan 2024, Goa.

Hersilia: 15 May 2024, Vaccine Depot Grounds, Belgaum.

Plexippus paykulli: 08 September 2023, Tilakwadi, Belgaum.

Crab Spider and Thyene imperialis: 04 December 2022, Govardhan Vilas, Udaipur.)