Called living fossils, horseshoe crabs are harmless creatures that have been swimming oceans for a few hundred million years. They predate dinosaurs and are closely related to spiders or scorpions. Every May and June, they crawl onto the beaches “from the Yucatan to Maine“ to mate and lay eggs in the sand in mass numbers.
At the same time, hungry Red Knot birds on the way to the Arctic from the southern tip of South America are looking for those millions of little green horseshoe crab eggs so that they can eat. The nourishment helps them gain energy so that they can finish their long migration and breed, as well.
In this KQED Science on the Spot, Rendezvous With Horseshoe Crabs, learn about these two species and what local teams are doing to protect the balance of their interdependency.
Photographer Steve Simonsen films an epic Caribbean hermit crabmass migration at Nanny Point, St. John, in the U.S. Virgin Islands. This video has gone viral, and it’s pretty clear as to why! How many thousands and thousands and thousands of crabs are on this beach?!
Hermit crabs, also known as soldier crabs, are found throughout the Caribbean islands and take part in a great migration en masse annually in August to mate. The crustaceans travel to the beach, leave their shells and enter the water to lay eggs, according to Smithosianmag.com. After spending two minutes in the water, Simonsen said the crabs turn around, return to land and make their way home.
People who live on St. John know this happens in August. I’ve never been able to see it or know when it happens,” said Simonsen, who plans to study the creature’s migrations, moon phases, tides and stake out beaches next August to see the phenomenon again.
The giant Japanese spider crab and its internet-classic molting video from Enoshima Aquarium in Fujisawa, Japan. The time-lapse was shot over six hours and is pretty incredible. More about these amazing creatures:
The Japanese spider crab has the greatest leg span of any arthropod, reaching 3.8 metres (12 ft) from claw to claw. The body may grow to a size of 40 cm or 16 in (carapace width) and the whole crab can weigh up to 41 pounds (19 kg)… It is reported to have a gentle disposition “in spite of its ferocious appearance”.
Japanese spider crabs are mostly found off the southern coasts of the Japanese island of Honshū, from Tokyo Bay to Kagoshima Prefecture… In its natural habitat, the Japanese spider crab feeds on shellfish and animal carcasses and may live for up to 100 years.
This class pet is named Shelby, and she is one very lucky hermit crab. Why? Because she’s about change into a brand new shell that fits her growing body. We’re lucky because we get to see her make the move.
The tip of the hermit crab’s abdomen is adapted to clasp strongly onto the columella of the snail shell.
As the hermit crab grows in size, it has to find a larger shell and abandon the previous one. This habit of living in a second hand shell gives rise to the popular name “hermit crab”, by analogy to a hermit who lives alone. Several hermit crab species, both terrestrial and marine, use “vacancy chains” to find new shells: when a new, bigger shell becomes available, hermit crabs gather around it and form a kind of queue from largest to smallest. When the largest crab moves into the new shell, the second biggest crab moves into the newly vacated shell, thereby making its previous shell available to the third crab, and so on.
But don’t be fooled by that name! Hermit crabs are actually social animals that prefer groups. From Hermit Crab Patch: “In the wild, hermit crabs live in large colonies and are commonly found piled up on one another when sleeping.”