The “good” kind, of course (as opposed to the “bad” kind you can get while having fun)…
Pony said earlier that I should write a piece about the crabs on the beach where we were staying. But there’s not a lot TO write about them – as apparently they are confusing to SCIENCE as well.
Once you figure out WHAT is making all those holes on the beach, you become aware that there are a LOT of them running around on the beach. They appear to be known as “ghost crabs” – and a lot of them live up to that name. They are nearly translucent as juveniles and quite often you can only see them out of the corner of your eye (the part that is sensitive to motion, which is handy if a wild beast, enemy soldier, or idiot making a poorly-indicated lane change is coming at you – but absolutely lacks clarity). They are scuttling away because you are MUCH larger than them and they move with a speed (they can make it from where you detect them to the relative safety of the water three feet away in under a second) that makes it even harder to focus ON them to see them – leaving you with the thought that you merely THOUGHT you saw something… or a GHOST! (Or, when you get to be MY age, you blame “floaters” in your eyes.)(Don’t laugh, youngsters – your time will come 🙂 )
Their relatively light (or, in this case, translucent) coloring and generally-nocturnal activities is where the “ghost” name comes from. As they get older, they seem to become easier to see – but hide and still move with the same astonishing speed when they need to… so maybe you STILL might just THINK you saw something…
Their need for speed is likely a product of necessity – they are food for a number of creatures including, presumably, humans. One story told of how early Hawaiians could tell the difference between a male and a female by their movements: males moved in jerky movements and the females moved in flowing ones (one assumes they took the males for food and let the females alone to continue to make NEW crabs).
And they have a place in the ecosystem – they eat EVERYTHING that can’t outrun them and will eat each other if they can (which might explain why the juveniles look and move the way they do). Size usually matters – although I saw one slightly-smaller one exercising “short man syndrome” and being quite aggressive against others slightly-larger than itself.
They prefer to stay OUT of the water (they have gills, need to stay moist because of it, but will drown – not to mention the number of reef fish who DO get close to the shore and have little problem crunching through a small shell like the juveniles have), but WILL “scuttle” (the descriptive name for crab movement) into the water if you approach and they either can’t, or are not comfortable with, running back to their hole in the sand (and, according to Wikipedia’s entry on the subject of “ghost crabs” in general, dash out quickly to the water to re-wet their gills – and since I read that, it does occur to me I saw this behavior). They seeming disappear into the water when they run there because you startled them – but on more than one occasion, I saw them just burrowing-in, since water-logged sand is generally faster and easier to dig into quickly.
They need to stay cool and their gills must be kept moist – so they spend their days in holes that they dig in the sand. In our stretch of beach, the difference between high-tide and low-tide was generally not more than 10 feet and at any given moment, there was probably less than four feet of damp beach that wasn’t under “threat” of a wave inundating a digging effort in the sand, ending abruptly at the end of the green commons area, so there wasn’t a lot of beach TO work with here (although I did notice a few holes in the “transition area” between the grassy area and the beach where there was more sand than soil).
They have eyes on stalk-like protrusions (much the same as “Mr. Krabs” in the “Spongebob” universe). They are extremely-sensitive to movement and will dive back into the hole or run for the water at the SLIGHTEST indication of a threat. Generally seemingly wise to the “I-will-wait-for-you-to-come-back-out-so-I-can-eat-you” thing, they are generally not seen again. I’m not sure if they WAIT you out, keeping an eye open from beneath the sand or waves – or just emerge at a different place or that “magical moment” when you give-up waiting on them.
But if you moved very slowly, you CAN sneak-up on them. And if you remain VERY still, they can be fun to watch… although it is probably helpful to also like watching ants working as well. So if you’re the action-packed video-games type, crab watching is probably not for you.
I have NO idea what kind of eating they might make – on our stretch of beach, something with a shell (not including legs and claws) larger than a 50-cent piece was a giant – and juveniles with a TOTAL body area (claws and all) smaller than a dime were more frequently encountered. So either they grow larger elsewhere – they were slightly larger in the very secluded area just east of the property and toward the fishpond nearby – or it takes a LOT of them suckers to make a pound! But the stories are told of digging-up crabs and eating them, so they must get to SOME size – or early Hawaiians also had some form of pupu that included crab finger-food.
The science behind them is a little harder. For a VERY long time, it was believed that the males placed their diggings in nice, neat pile (the better to attract a mate), while females and juveniles just tossed their sand any old which way, because they weren’t bothered with the need to attract a mate.
Marine biologists NOW believe that there are TWO distinct species that are strangely-coexisting with each other – the one kind that THROWS the sand any old which way – and the neat “Felix Unger” types. WHY there is distinction, no one seems to know yet. Heck – the idea of two distinct species apparently hasn’t made it’s way around the Internet universe yet – the Waikiki Aquarium in Honolulu (who should know sea life better than anyone, right?) still holds these are male/female distinctions.
Ah, science. And the academics wonder why people question “global warming” in the middle of a blizzard. They can’t even get the crab story straight yet. (My tirade on scientists believing the world was flat is a rant for another time. As a preview, one of my favorite lines from “Men in Black:” “Fifteen hundred years ago everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you’ll know tomorrow.”) 🙂
I’m also not quite so sure about that “co-existence” thing – if they get along SO well, then why isn’t there any cross-breeding between the species? Or is there and science just hasn’t discovered the version that makes neat sand piles and then runs out and jumps on it to scatter it? Or vice versa?”
Or is it a “territorial” or “male” thing that you see the fights that you do? It’s kinda of fuzzy (to me, anyway – but I AM a caveman, so…) as to why fights over holes occur (there is nothing I read, by the way, that females – who lay eggs in the sea – even GO into holes to do that “crab thang”). One imagines it is for the hole that has been dug by another (and to the extent you CAN tell the difference between two of them, I think I’ve only seen a resident lose and be driven away once), but the holes all fill-in – and need to be dug out again – with the high-tide, an event that happens roughly every twelve-hours, so if you manage to steal one, you’re going to have to start over again (hmmm… maybe caveman DOES have a larger brain than crab – or at least more smarts, maybe).
But fight they do – for whatever reason. The loser – usually the “visitor” – then continues down the beach as if nothing has happened. Maybe to pick on another hole, maybe to eat something smaller than itself – and it is interesting to watch behaviors among them there as well, especially in the juveniles: they wait until the seemingly last moment, then run as fast as they can – but just far-enough to where they think they aren’t being chased – and it’s rare that they are (as opposed to running straight for the water or into their hole when a human approaches).
Oh – and about that running thing: they are able to change direction of scuttling instantaneously, merely by choosing which legs are the ones that will take them the direction they want to go suddenly – all without losing speed. I can think of several sports where THAT might be an asset!
But otherwise – sorry, Pony – I really can’t tell you a lot about the darn things… 🙂