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

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) blurred view of vast number of individuals moving along their annual migration route, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing closed road, during annual migration, Christmas Island, Indian Ocean, Australian Territory, November 2009.

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing road in huge numbers during annual migration, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) arriving in huge numbers, at coast for spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) gatthered together on beach the day before spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) massing on coastal rocks, the morning after spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) shortly before sunrise sitting on rock ready for spawning, Christmas Island, Indian Ocean, Australian Territory

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

Solvin Zankl / Anomuran larva of a Hermit crab, Atlantic ocean

Juergen Freund / Thousands of Christmas Island Red crabs on rocky shore (Gecarcoidea natalis)

Juergen Freund / Christmas Island red crab (Gecarcoidea natalis) wearing Father Christmas hat, Christmas Island, Indian Ocean