Tuesday, 21 September 2010

Very Junior Coconut Crab

This is a fairly junior Coconut Crab (Birgus latro), a crab almost completely land-adapted, except for about a month in the sea in its extreme youth.

This particular one has been visiting my house regularly over the past few years, but I didn't recognise its species.

This very crab has woken me up at night by scrabbling up my book-cases, and falling off.

It has been using the very same Fox Shell (Pleuroploca trapezium) for all this time, but it's getting a bit battered, mainly because I got fed up with it, and used to kick it into the middle distance every time it turned up on my front doorstep.

These, to the right, are part of a harvest of shell-bearing crabs from my garden, collected by my neighbour's little boy. You can probably recognise the fox shell shown above at the top centre. I can't be sure, because I didn't recognise them at the time, but I would bet that most of them are Birgus latro wannabes.

In which case, most of them have very little chance of ever making it to monster size. There are simply not enough large shells on land, or washed up to the top of the beach, to give them ways to grow.

Probably many of these shells will be used over and over again, in a crab's vain hopes of growing up. There is a lot of competition for new houses. Many are called but few are chosen.

Some may well turn into monster terror crabs, if they get a lot more chances, but I think most will have run out of large shells to inhabit in the meantime.

Because of the offshore reef in GL we get very few wavy storms within the lagoon, so very few larger shells get washed up. Most that do end up on land have been harvested by local fishermen. Certain of those, like baler shells, helmet shells, and conchs, are plenty large enough, but have strangely shaped apertures that can't accomodate a crab comfortably. They like a circular aperture that they can easily plug with their major claw and one leg.

About the only local shell that a large Birgus latro can use is a Triton, but these are becoming very rare. If one is seen walking around, the crab is casually sacrificed so the shell can be sold.

1 comment:

phileklund said...

Are some of these Coenobita? How do you tell the difference?