The Ambush of the Sally Lightfoot Crab

A Galapagos wildlife cruise introduces nature lovers to some of the most remarkable marine and terrestrial animals on the planet. While the Giant Tortoise and the Marine Iguana are probably the best known of the archipelago's species, the quirky Sally Lightfoot Crab also garners its fair share of attention, and its intense blue and red livery is a common sight scuttling along the islands' shores and in the shallows.

Eat and Be Eaten

Grapsus grapsus has a hugely diverse diet, feeding on everything from sea lion placenta to ticks and organic matter washed up on the shore. The species is by no means under threat (in fact it’s probably one of the most commonly seen by those on a Galapagos wildlife cruise), but it does have its predators. The crab is enjoyed not only by herons, tuna and introduced species like cats, dogs and rats, but also by eels and octopuses. What's different about the latter two predators, however, is their technique of ambushing the crabs from under the water.

The ambushing tactics of eels and octopuses preying on the Sally Lightfoot was the subject of an episode of the excellent BBC series, Blue Planet II, with Sir David Attenborough. While this particular filming took place in Brazil, as the crabs made their way to seaweed pastures for feeding, it makes for compelling viewing for anyone planning a Galapagos wildlife holiday. Understanding the potentially deadly trials these colourful crustaceans face goes a long way to explaining their infamous skittishness and their seeming reluctance to get their feet wet.

Eels on the Attack

The Moray Eel is the crab's deadliest enemy, with its blunt teeth specially designed to be able to latch on and crush their shell. When the crabs travel to their feeding grounds across the rocky shoreline at low tide, the eels lie in wait in the shallows – biding their time to make their move. As the crabs scuttle and leap across the rocks, the eels stalk them from beneath the surface, before launching themselves out of the water to claim their prey in their powerful jaws. Even if they miss at the first attempt, they continue to stalk, often crossing rocks and land to get to their quarry. Nowhere is safe, and even the crabs that do make it through to the seaweed pastures only have a few hours before the tide turns and they must face the return journey and do it all again.

Octopus Ambush

The octopus is another mortal enemy of the Sally Lightfoot and it too lies in wait for the pilgrimage to the crabs’ feeding grounds. Triggered by any movement above the surface of the water, the octopuses release their far-reaching tentacles to ensnare their prey as they scamper across the rocks and, incredibly, they're even able to pursue them over land and rocks.

Recommended Viewing

The Blue Planet (Coasts, episode 6) captures the ambush of the Sally Lightfoot in all its mesmerising glory, with the segment taking three weeks to film. Interestingly, the producers had previously been unaware of the octopuses’ stalking tactics, and had only planned on filming the eels. For anyone planning to embark on a Galapagos wildlife cruise, the episode is highly recommended viewing, providing an insight into just one aspect of the fascinating behind-the-scenes trials and tribulations of the inhabitants of this magnificent archipelago.