John Shaw / Sally lightfoot crabs (Grapsus grapsus) on the beach at Puerto Egas, Santiago Island, Galapagos, May.

Andy Rouse / Sally lightfoot crab, (Grapsus grapsus), feeding on marine iguana parasites and dead skin, Galapagos

Alex Mustard / Portrait of Sally lightfoot crab (Grapsus grapsus) on a beach. San Cristobal Island, Galapagos Islands, Ecuador. Tropical East Pacific Ocean.

Tui De Roy / Dead Sally-lightfoot crab (Grapsus grapsus) washed up in surf, Puerto Egas, James Bay, Santiago Island, Galapagos, Ecuador, May.

Tui De Roy / Marine Iguana (Amblyrhynchus cristatus) breeding male basking with Sally Lightfoot Crab (Grapsus grapsus) scavenging dead skin, Hood Island, Galapagos Islands, Ecuador

Michio Hoshino / Marine Iguana (Amblyrhynchus cristatus) group with Sally Lightfoot Crabs (Grapsus grapsus), Galapagos Islands, Ecuador

Tui De Roy / Sally Lightfoot Crab (Grapsus grapsus) pair sharing boulder with Marine Iguanas (Amblyrhynchus cristatus) to escape high tide, Mosquera Island, Galapagos Islands, Ecuador

Tui De Roy / Sally Lightfoot Crab (Grapsus grapsus) group sharing boulder with Marine Iguana (Amblyrhynchus cristatus) trio to escape high tide, Mosquera Island, Galapagos Islands, Ecuador

Tui De Roy / Sally Lightfoot Crab (Grapsus grapsus) group sharing boulder with three Marine Iguana (Amblyrhynchus cristatus) group to escape high tide, Mosquera Island, Galapagos Islands, Ecuador

Tui De Roy / Sally Lightfoot Crab (Grapsus grapsus) feeding along tide pool edge, Punta Espinosa, Fernandina Island, Galapagos Islands, Ecuador

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi). Tenerife, Canary Islands.

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi). Tenerife, Canary Islands.