Footprints in the Sand on Sandy Island

Sandy Island, Carriacou, Grenada viewed from a hilltop on Carriacou.  Ice Floe is furthest to the right.
Duhkxy has become a capable and comfortable swimmer.  He howls with delight when he sees me don my bathing suit and we need to be very careful to make sure he doesn’t land on our heads when he launches himself into the water after us.

Our Evening Routine

Each evening we swim with Duhkxy to Sandy Island to walk the beach, and visit the hermit crabs.  The evening before, they created beautiful new patterns in the soft sand as they travel to and fro in search of food, new shells, and whatever else they have a hankering for.
Their footprints tell the tale of their long journeys, and they leave very little of their terrain unexplored.
An island bird’s footprints lay atop the beautiful quilt-like pattern laid down by hermit crabs
A hermit crab crossroad
Largest land hermit crab we saw on Sandy Island (~3-4 in)

Hermit crabs are remarkable creatures.  They do not have a protective shell covering their abdomens.  They must borrow one left behind by a dead snail or other animal.  Having searched the beach on Sandy Island for months, I can attest to the fact that there are not many shells and the most beautiful ones invariably have been taken by a hermit crab.  As they grow, they must find larger shells and on occasion they may do so in a cooperative manner.

When a hermit crab (Crab 1), in need of a larger shell, comes across one that is a bit too large, it may stay by this shell in hope

that a larger hermit crab (Crab 2) may come along also looking for a new shell. If Crab 2 takes the larger empty shell, its previous shell may be the perfect size for Crab 1.

Sometimes, a number of hermit crabs line up in size order waiting for the biggest one in the line to start the switch.  Then each crab exchanges its shell for the next larger one that has just been vacated.  Take a moment to see this happen at
https://www.youtube.com/watch?v=f1dnocPQXDQ

Recognizing the shortage of shells on the island I felt compelled to return suitable shells from my collection to areas with large populations of the crabs.  In less than 15 minutes, an interested crab came by to look at a three quarter inch blue shell I had returned.  At this point, in the next photo, the small hermit crab has already examined the blue shell, turned it on its side and appears to have positioned itself to line up the shell openings.

In the next regrettably fuzzy photo, the smaller crab has inserted its abdomen in the larger shell.

Within the next several minutes another hermit crab approached and examined the newly empty shell.

However, it ultimately deemed it not a good trade and went on its way.  By the following morning about half of the shells I had distributed were gone, with very small empty shells in their place.

Land hermit crabs mate on land and the female carries the eggs until maturity (~ 1 month).  At that time, she distributes them in salt water and they immediately burst, releasing the immature hermit crab.  Each crab will undergo a number of life stages in the sea, and upon acquiring a shell, they begin to spend some time on land.  Their final metamorphosis occurs buried in the sand at which time their gills are modified such that the hermit crab can breath air.  At this point, a land hermit crab will drown if submerged too long in water.

The approximate size of of the hermit crabs shown below are less than two inches in diameter, but we have seen some as small as an eighth of an inch and as big as George’s fist (first photos above).  All of these hermit crabs are land crabs.  They must periodically replenish a supply of water that they carry in their shells.  A hermit crab without its shell is not only in danger of becoming someone’s snack, they will dehydrate quickly and die.

Tucked all the way into its beautiful shell you can see the brightly colored claws of these Caribbean land hermit crabs.
This odd looking hermit crab shell was wearing the calcareous shell of a tube worm (also photo below)

Our initial encounters were with hermit crabs in the sand.

Later we found them climbing palm trees and congregating and feasting on the foliage of the sea grape.  The following photos are representative of the majority of the hermit crabs we encountered.

Addendum, added June 26 – Shortly after publishing this post, the hermit crabs all but disappeared on Sandy Island.  Most had not returned by the time we had to leave Sandy Island, and those that did were tiny.   We concluded they had buried themselves in the sand and started a synchronous molt.  The time it takes for a crab to complete a molt varies. As a general rule, the larger the crab, the longer the whole process will take. It is not unusual for an average-sized crab to spend about four to eight weeks going through the whole process, during which time it may stay completely buried in the sand.



Stay safe and well.  The worst of the first wave of Covid 19 is passed but new infections are being recorded at a rate around 20,000 per day – BE CAREFUL!!  We may choose to believe that there will be no second wave, but most likely it is at best a few months away.  Try to take these limited summer months to prepare to the extent that you can.

Jjj