I never would have described crabs as interesting or fun to watch, until I saw Sally Lightfoot Crabs while visiting the Galapagos.
Sally Lightfoot Crabs (Grapsus Grapsus) are a common sight in the Galapagos and are a joy to watch. They really catch the eye because they are bright red with a white/blue underbelly, and make a dramatic contrast against the black volcanic rock along the shore line. We saw them in large groups scurrying over the rocks in search of food. We also saw them climbing up the wooden poles on the wharf at the Aventura Lodge on Santa Cruz Island.
They have five sets of legs (ten legs in total) four sets along the sides and one set in front. The legs along the sides are very pointy and have incredible holding power. I watched a group at high tide holding onto the concrete surface of a wharf. The waves continued to wash over them but they did not lose their footing. They can also climb the wet slippery sides of rocks and easily scale the vertical sides of a wooden pole.
Their front set of legs have claws at the ends. It was very interesting to watch them use their claws to pick up little bits of algae and whatever else eatable they could find. As they find a little piece of food they pick it up with one claw and quickly put it in their mouth, while the other claw is busy doing the same thing. The claws are put to the mouth one after another, as one claw reaches the mouth the other is picking up another piece of food. This is done very quickly and looks very comical.
While I was watching them crawl over the rocks I was surprised to see that they could jump from one rock to another. It was also surprising when Bryan and Drew told me that they had seen them move across the top of the water. They said it looked like they were walking on water. I did a little reading about them and found out that their ability to move across the top of the water is probably where they get their name “Sally Lightfoot” from.
The adults are bright red and orange with a whitish-blue belly. They grow up to about 20 centimeters across and look kind of like large red spiders. Young Sally Lightfoot crabs are black with red spots, they take on more red with each new change of shell. I didn’t notice the young black ones at first because they blended so well with the black volcanic rock.
I’m glad I took some time to watch the Sally Lightfoot crabs, it was a great experience.