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Robber Crab

Posted by
Darkelf Photography (Perth, Australia) on 5 April 2023 in Animal & Insect and Portfolio.

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I could not resist posting this photo of a Robber Crab, also known regularly as Coconut Crab. Christmas Island has the largest protected population of these giant crustaceans, and they are just magnificent. As much as the island is most famous for its red crabs, robber crabs were my absolute favourites. They feed mostly on fleshy fruits, nuts, seeds, but they will eat other organic matter if they can get their claws on it. Anything left unattended on the ground is a potential source of food, which they will investigate and often carry away – thereby getting the alternative name of "robber crab". We have been advised beforehand to hang our bags from a tree branch while camping or swimming instead of leaving it on the ground to avoid it being quickly taken away. They will steal just about anything - cameras, shoes, rucksacks, camping gear and even break open eskies. They are also known for climbing up doors outside kitchens where food is cooking.

We could spot robber crabs all around the island and especially in darker and more rocky areas. They like to come out at night and on dark overcast days but rainforest floor is often dark enough for them as well with limited sunlight reaching down to the ground. They can actually climb rocks and trees, and we were able to witness that on a couple of occasions. Often when we found one, there would be a few more hanging about. They can measure up to one metre across when they open up their arms, and weight up to four kilograms. So they are not tiny and they do make for quite a sight in real life. We had to be careful when driving around to avoid driving over the crabs, especially at dusk or dawn, when they were ready to being their nightly wanderings.

This is fellow is the one from a previous photo taken at the giant strangler fig. They are usually rather slow and placid, and they pose no danger to visitors. Because of that, I was able to get in very close to this one and photograph it in very low light. Walking between the vast root system of the fig tree was not really suitable for tripod use but it gave me chance to practice shooting handheld in low light with my longer lens. I went for a wide open aperture of f/2.8 and pushed the ISO to 1600. I could have pushed the ISO higher but I did not want to have too much noise in the photos. Resulting shutter speed was still quite long at 1/20 sec but I went slow and steady to see if I could get some reasonable images. I have to say, I was very pleased to get most of them sharp and free from motion blur. I focused right in on the eyes and my aim was to get the eyes and the main body in focus. I was not too worried about the outer limbs being outside the focal plane. I was also careful not to cut off its long antennae to ensure that it stayed within the frame.

What attracted me to this one especially, was its blue colour. Most of the ones we saw had varied hues or red, bronze and orange, but there was a smaller number of these wonderful blue coloured crabs. I do not believe that gender or age have anything to do with the colour. It could be just a natural variation. The blue ones did stand out though, and I was always really happy to see one of them during our journeys.

If you are interested to find out more, there is a good documentary about coconut crabs here. I might post a few more photos of these fine creatures in the future. They were truly fascinating and added another level to our experience at Christmas Island.

Canon EOS 5D Mark IV 1/20 second F/2.8 ISO 1600 135 mm

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