© 2007 All Rights Reserved. Do not distribute or repurpose this work without written permission from the copyright holder(s).
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Every year around the end of the October, the red crabs of Christmas Island begin their march. Up to 100 million individuals leave their burrows in the forest and head to the shore in a scarlet tide of legs, claws and carapaces extensive enough to be seen from the air. They are driven by the most basic of biological imperatives: to spawn.
The islanders take the crustacean migration in good humour, closing roads and erecting diversions in an effort to curtail crab casualties and the tattering of motor vehicle tyres. After all, the annual show is a symbol of the distinctiveness of the Indian Ocean territory, and a big draw for tourists, naturalists, wildlife photographers, and documentary-makers worldwide.
Many visitors are impressed both by the size of the migration and by the islanders’ obvious concern for the crabs. Indeed, an outsider could be forgiven for believing that the spectacle has been an annual occurrence at Christmas Island since time immemorial, one surely destined to astonish countless future generations.
But the grand scale of the annual march— if not its very existence— is threatened by a foe far more ferocious than road traffic or the clumsy feet of camera-wielding tourists. And the origin of the migration itself is perhaps more recent, and more tainted, than many would believe. The story is one of inter-species meddling, conflict, and extinction, set in the context of a fragile island ecology. It involves protagonists of a two-legged, four-legged, six-legged and eight-legged variety.
Christmas Island red crabs (Gecarcoidea natalis) are terrestrial, spending most of their lives on land. More specifically, they spend most of their lives on this one particular chunk of land, since the species can be found nowhere else on Earth. For much of the year the crabs are a very visible presence, whether migrating or not. As one of the island’s ‘keystone species’, they play a vital housekeeping role in the inland rain forest, scavenging fallen fruit, leaves, weeds, seedlings and carrion; recycling nutrients; and aerating the soil with their burrows. But the crabs must make one concession to their aquatic evolutionary origins: the larval form of the crab has primitive gills which only function in the sea. For this reason all reproductive activity takes place by the shore.
With the increase in humidity that comes in October or November, the males begin their perilous march, joined a few days later by the females. The throngs of arthropods migrate en masse, crossing the landscape as a quivering red wave. The island’s thoroughfares quickly become littered with smashed corpses, prompting locals to detour traffic and use shovels to clear roads as needed. Upon reaching the shore the males engage in frenzied bouts of digging and fighting, building and defending temporary tunnels to woo the females. When they arrive, the females peruse the wares being offered, and deeply ingrained instincts tell them to select the males with the largest, best-formed burrows. Suitably impressed females are enticed inside, where mating usually occurs. Afterwards the exhausted males take their leave and stagger back inland.
After 12-13 broody days in the burrows, the females release their eggs in the ocean at the turn of a pre-dawn high tide. They release the eggs together over six or so consecutive nights, turning the coast of Christmas Island into a huge birthing pool. Then they return inland themselves. The larvae hatch and grow in the sea for about a month before amassing back at the water’s edge, ready to moult into tiny air-breathing adult crabs. Thus in some years the renowned migration of the fully-grown crabs to the shore is matched by an equally impressive flood of dainty young minicrabs going the opposite direction a few weeks later. In other years the larval population is decimated by water-borne predators, but because it takes about four years for the young land crabs to reach breeding maturity, the fluctuations even out in the longer term and a consistently large population is maintained.
The human presence on the island dates back little more than a hundred years. Christmas Island was named by Captain William Mynors of the British East India Company when he stopped there on 25th December 1643, although it wasn’t until 1888 that the first permanent settlement was established.
Early descriptions of Christmas Island’s wildlife make an intriguing and surprising omission. In an 1888 report made to London’s Geographical Society, Captain Aldrich of the Royal Navy describes plentiful powerful coconut-cracking robber crabs –found throughout the Pacific and Indian Ocean islands— and a profusion of mysterious rats on the island, but he fails to make any mention of the now-pervasive red crabs. The extent of the rat infestation can be inferred from his description of a night on the island:
“We brought hammocks with us, and slung them under the trees; mine was between two and three feet from the ground, and three rats I know came over me as I lay in it, how many more when I was asleep I have no means of telling.”
Other early accounts attest to the swarming abundance of the enigmatic rodents, but few mention the island’s red crabs. Subsequently the rats were identified as another endemic species, the Maclear’s rat. It seems that in the late 19th century, these rats were as numerous as the red crabs are today. Like the crabs they were scavenging creatures that lived in burrows on the forest floor, but the exact role they played in the ecology of the island will forever remain a mystery— for by 1903 the species was extinct, wiped out by an epidemic of trypanosome parasites introduced by ship-borne black rats.
Some scientists have hypothesized a link between the decline and extinction of the Maclear’s rat in the early twentieth century and an ensuing explosion in red crab numbers. They propose that the native rats previously kept the red crab population in check, and that with the demise of the rodents, crab numbers increased– giving rise to the dramatic annual breeding migration ironically celebrated today as a ‘Wonder of Nature.’
Along with disease-carrying black rats, Christmas Island’s settlers brought other invasive species with them— with one in particular having a less beneficial effect on the red crabs. The troublesome stowaways included cats, house mice, and well over 50 invertebrate species including a type of ant named the yellow crazy ant. By 1934 these intruder ants were firmly established on the island.
For fifty years the newcomer— named both for its colour and for its frisky response to being poked— seemed to settle quietly into the laid-back rhythms of tropical island life, enjoying relative harmony with the native flora and fauna. The ants established scattered single-queen nests, each with a discrete territory which was vigorously defended from the other ant colonies. But by 1989, the yellow crazies began to do something quite out of character: they began to form multi-queened supercolonies with numerous queens and much larger territories. This created areas with dense populations of genetically-related ants capable of close and deadly cooperation.
Supercolonies can expand rapidly, with the high ant density having a devastating effect on the surrounding wildlife. Birds and larger animals succumb to a spray of formic acid squirted by the aggressive insects, their corpses later providing a handy source of protein. Despite their impressive looking armour, red crabs are not immune: the ants’ formic acid initially blinds, then kills the crabs. When migrating across supercolony-controlled areas, almost all crustaceans perish.
The death toll among the red crabs has been high. By 2002 it was estimated that the ants had killed 20-25 million, a quarter of the original population. Other creatures facing a similar onslaught include a bird called the Abbot’s Booby, and a shy mammal named the Christmas Island Shrew. Both of these endemic species now face ant-induced extinction. In ant-infested areas of the island where the ‘keystone’ crabs no longer live, young seedlings, weeds, and a species of stinging tree grow rampant, fundamentally altering the structure of the rain forest.
Realizing that the loss of the crabs could spell eco-disaster (both -nomic and -logical), Christmas’ Australian authorities instituted poison-baiting schemes. In 2003, they deployed air power: a helicopter was used to drop 12 tonnes of irresistibly tasty ‘fipronil’-laced fish meal onto supercolony-held territory. Although ant density was reduced by 98% in the treated areas, recent years have seen the crazy ants reestablish themselves. It remains to be seen whether future ant abatement efforts will be equally successful.
The reasons why the crazy ants formed supercolonies in the first place are obscure— but it is known that in other situations where invasive species have spread into new areas, similar transformations in ant behaviour have occurred. In 2000, researchers identified a probable 6000 km-long supercolony of invasive Argentine ants stretching along the entire coast of southern Europe.
Genetic studies of such populations may provide some answers, but nobody can yet say how the inter-species skirmishes of Christmas Island will play out. What is certain is that the last century or so of human settlement— and particularly the associated introduction of invasive species— has caused considerable disruption to the island’s previously isolated ecosystem. There are both winners and losers in this ongoing process, and one very visible species may well have had it both ways. Visitors intending to view the grand spectacle of the red crab migration this year may want to remember the Maclear’s rat, and hope that the crabs of Christmas manage to avoid a similar fate. And they may want to pack some ant repellent.
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At first this is a truly fantastic spectacle to behold. Then it becomes a pain as detours appear blocking some roads. In other areas traffic slows to a crawl, but you still wind up squashing some of the little devils.
While working in the Pacific I tended to take a daily night jog. I enjoyed this best when the fluorescent tide was in. The incoming waves looked like the crests were on fire, very interesting and very cool. Especially when you went swimming and the water would fluoresce around you, leaving a slowly dissipating fire trail behind you.
The part I did not enjoy about my night jogs was when the moon was out. During these times the crabs would cover the beach. As you jog it looks like the ground is moving, twisting, flowing all around you. That’s how many crabs would be on the beach. Every so often I would inadvertently crunch one of the little buggers beneath my feet, when some would flow into me rather than away. Ew.
How long before we must bow before our Ant Overlords?
You know when you are sleeping and you swear to God that you feel something touch your leg/feet.
Yes this article has not helped that in ANY WAY whatsoever.
Damn Interesting though! Great work.
Extremely interesting, and extremely sad to know we are the main vector of extinction. As the Juan Fernandez Island of the Selkirk castaway, the Galapagos Islands are to be decimated by the ravaging goats introduced by settlers at the beginning of the century. What a great loss the extinction of terrestrial mammals like the Maclear’s rat, similar in magnitude and fashion to the extinction of the Galpagos endemic rodents. The introduction of parasites and pathogens is probably a constant in human colonization. Influenza, smallpox, measles, and typhus fever were among the first European diseases imported to the Americas, estimates suggest many millions perished.
Let us not forget that we’re not the only harbingers of destruction. Sure, we make it easier, but history is replete with examples of land bridges allowing access to formerly inaccessible areas. What is called natural selection in those cases is being marked a sad and terrible thing (by some) in this and other cases. What is the difference, really? We are naught but land bridges, my friends!
That said, I’d love to see the Christmas Island migrations, were they not so freakin’ creepy. I don’t mind crabs one bit, but crushing them? I’m sorry, I don’t want crab juice on my tires/shoes. And the smell! UGH!
And that, my friends, is what NIGHTMARES are made of!!!! eeek – now I’ve got the creepy-crawlies…lol
Seriously, though – very di article! I’d be interesting in seeing some bird’s-eye view pictures of that.
Well Brandie, if you what the shivers check out this video on The Christmas Crab. ;)
I am by no means an expert on the subject, but I can recall reading something a while back about ant supercolonies being caused by a lack of genetic diversity in the population.
Normally, ant species create nests with a single queen and will be extremely aggressive toward any ants from other queens in other nests. Assume that these two nests are the only two on the island. In the event that one is able to annihilate the other, the victor is left without any competition. With no one to fight, they instead direct their resources toward rapid expansion. Eventually, the queen produces another queen which can go on to create another nest. The thing is, these nests are directly related at the genetic level. Therefore, the ants’ xenophobic little aggression triggers don’t get set off. They recognize the other ants as those from their own ‘tribe’ and treat them as such. Once all the ant tribes in a particular habitat except one are dead, all the ants are related and can go on to form a supercolony.
Thank you for the well-written article. I have no idea where Christmas Island is. Would it be possible to include a map in articles such as these?
A map of where to find Christmas Island? Here you go: http://www.environment.gov.au/parks/christmas/index.html
One thing that might make us different is that we have the capacity to learn through generations… will we continue to do it, is the question. As we gain more control over GM / synth-bio (I made that up but I like it) we risk making the same mistakes. It will be interesting to see what we, as a species, have learnt.
“We have the capacity to learn through generations”. That reminds me of the “meme” concept by Richard Dawkins. Not all learned behavior or gained knowledge is positive however, there are many things we take as granted, but for which we do not have an atom of evidence. For example, during the 16th-19th century many people learned that slavery was good and natural. During the early 20th century many people believed in the supremacy of a particular race over the others. The examples are numerous, in which “memes” become virulent and destructible phenomena. Gratefully, we have the tools of science and reason to get closer to the truth.
This might sound weird, but are those crabs comestible? hmmmmm… crab cakes….
eeeeeeeeeeeeek – I watched the YouTube video of footage of the migrations – I guess I’m easily creeped out…LOL…especially the migration of the baby crabs back to the island’s interior!
Personally, I prefer the crabs over rats. The thought of that many rats gives me the willies.
I had no idea that ants formed supercolonies. Now you’ve given me something to research over the weekend. Google here I come.
I’ve read some where that the flesh is bitter and unedible.
Very cool, I’m adding Christmas Island to my list of ‘places to see before I die’ :)
Also, “Afterwards the exhausted males take their leave and stagger back inland.” [tongue in cheek], I’ve been there, mate…
And also, “eco-disaster (both -nomic and -logical),” very nicely constructed, only clever minds can do that.
DI article, thank you.
I knew ants were formidable creatures, but these ones are downright horrific.
This reminds me of when I was 13 or so and traveled to England with my family. We often visited gardens (oh, real fun for 13 year olds), and on one instance, while walking on a path, we kind of noticed that it had a strange wavy effect while we were walking on it, and the ground felt strange (like shredded rubber, which some schools used to use in playground areas). My sister and I looked down, and to our chagrin noticed that were were in the middle of a massive frog migration- frogs no larger than an American quarter (the coin, not some weird measure of scale) that were innumerable. It dawned on us pretty quickly that the squishing sensation we had was from converting the living frogs into not-living frogs, and we freaked out. We took care not to crush any more frogs on the path as we walked down it, but we inevitably did. Sigh. Poor frogs.
And I just remembered on a related not that we’d often be really late walking to elementary school because we’d try to get as many earthworms stranded by the rain off of the sidewalk (note we live in Washington State, so this would happen about…every day).
So I’m sure if I was on Christmas Island, I’d be one of the pricks telling everyone to get off the streets and stop killing the crabs with their big dumb feet and car tyres.
*shiver* That’s pretty cool, but at the same time creepy. I can just imagine it. Majestic, but at the same time you want to find a very tall place and stay there.
This is my first ever post, as I have only recently discovered this fantastic site, maybe my new favorite website.
Christopher, you made me LMAO in the most literal sense of the word.
Yoweigh, your explanation for the ant super colonies is feasible and extremely well put, thank you for elaborating on that.
I am officially scared shitless of Yellow Crazy Ants.
For some reason, the idea of a three-way war between the crabs, the crazy ants, and the humans is so irresistibly awesome.
Why has their not evolved a California style rat, a Chicago rat or a New York City Rat, etc.? I guess rats just don’t evolve at the same rate as other things like pizza.
Hey there Kevin, welcome to this fantastic site. At the risk of sounding d.s. (damn stupid) on the d.i. (damn interesting) site I am curious… what does LMAO stand for? I must be getting old and I don’t understand all of these new-fangled acronyms. I think I lost track after LOL. Doh!
You and I both are scared
And just when you thought you had crazy Uncles……… :)
With all the crap we randomly introduced to new places we found back in the day, it’s amazing we didn’t totally destroy the enviroment 0_o
Laughing My A** Off
Those ants are truly fearsome creatures – I love the way they formed a supercolony not after a hundred million years, but in such a short span of time.
Well, in a sense we did; many places are very different than they would have been had they remained sans-human intervention. But what people seem to simply omit from their logical processes is that nature does the same thing to itself all the time. Heck, even these secluded islands were at one time stripped of their natural splendor by the invading birds/plants/turtles/what have you — with no human intervention in sight.
Humans are blamable for plenty of things in this world, but the transmission of life to new locales is not one of them. It is as natural as…er, eh…nature.
I find the bit with the yellow crazy ant quite interesting. I remember my first awareness of ants being dangerous was when I watched the film The Naked Jungle as a kid.
So what actually happens when you poke those Ants?
Thanks, kjdsahf, it can also mean “Light Many Ants On fire” or “Lift Mighty Atrophied Ostriches” or “Lick Mostly Apples and Oranges” but I was going for Laugh My A** Off as you so eloquently put.
Real Time Strategy, anyone? I’d buy that.
It reminds me of the giant ant levels on Command & Conquer Red Alert: Counterstrike.
Actually, sometimes we do introduce life to new places deliberately. Kudzu was introduced to the U.S. that way. It often grows fast enough that one can watch it grow. Kind of neat to see,but hard to get rid of it.
Thanks for enlightening me on LMAO. I’m going to use that from now on! :) In fact I will try to LMAO at least once a day from here on out! :) The Japanese beetle has caused some extensive damage to crops in the US. There are also those blasted killer bees and the West Nile Virus carried via mosquitos that made their way into North America. I read somewhere that the US also has a high number of wild cat species living here as dometicated pets or in pastures all over the country. Somehow, I think that if a lion got away it would be able to fend for itself- frightening though! Lots of places import parrots and finches as pets and release them into the wild. Aren’t there some wild exotic birds in Los Angeles now because of that? What about all of those excess rabbits in Australia? Sometimes also when a species gets re-introduced into a location it will multiply many times over. I’ve seen it with the Canadian Goose. This type of goose used to be low in numbers, and now you can hear them noisly honking and carrying on all throughout where I live in the Midwest. They are so noisy that I understand why people used to shoot them. LMAO. :)
The part about supercolonies was particularly interesting. Here in the States, yellow jackets are starting to do that. I saw a picture in the news of an old car, like a Plymouth Valiant or something, that was completely filled with yellow jackets nests, with the grey paper sprawling everywhere in bizarre formations. They said it must have had at least 10 queens in it.
Yes, there are definitely some wild exotic birds in the Los Angeles area. I know, because there is this group of peacocks that wander around my street.
…and let’s not forget the blue meanies!
I can accept LOL…but LMAO! How is that be possible?
Maybe that’s another good idea for DI article!!!
I was using “blamable” more in context of being responsible for harm done (and in this case, harm done that nature can’t replicate). Wasn’t the best word choice, apparently ;)
You don’t know the half of it if LMAO is extreme to you. How about AFAIK [as far as I know] or IMHO[in my humble opinion]? IDK [I don’t know], ROFLMAO [rolling on the floor, laughing my ass off], GTFO [get the fudge out], etc? Not to mention the context specific ones…MMO’s are notorious for their extensive use of acronyms.
But to get back on topic, I’d like to see what would happen if they introduced yellow ant predators into the environment, and then just kept introducing natural predators until everything evened itself out, like in that episode of the Simpsons. Yeah, we’d probably lose a few unique species, but it’s isolation means that the effects of such won’t exactly be detrimental. It would be a good bio-experiment 8-]
Hey if they can have a hobo code
shorly there can be a youth code
brb = Be right back
wb = Welcome back
lol = Laughing out loud
lmao = Laughing my ass off
roflmao = Rolling on floor laughing my ass off
and my favorite LSHINTSMKTKFPIMS = Laughing So Hard I Need Too Squeeze My Knees Too Keep From Pissing In My Shoes
and many many more that are more like a new concise language than acronyms
Eg L8r = later or Cya = see you and of course combinations of these like Cya L8r
and the smilies :-0 ;-) :-D
there is a new written language immerging and very soon is going the become a type of standard on the internet
…well then, you left out some of oldy-moldy, all time classics, like…
…and then for the armed service type folks out there…there’s the military spec…
MILTDD-41 (Make It Like The Damn Drawing For Once). :-)
Believe or not i have eaten similar red land crabs, must be slight genetic difference. Damn Tasty
Here’s a few more IT support acronyms for you.
PEBKAC – Problem Exists Between Keyboard and Chair (IE dumb user)
ID ten T Error – [ID10T = idiot]
Layer 8 Error – I believe this goes back to Unix architecture which has 7 layers between the most basic layer and the user. The user would be the 8th layer. I think I’ve got the numbers right there, but I never knew too much about Unix.
As you can see, alot of these are just ways of hiding the fact that a specific issue was caused by a user, they get used in support call text occasionally.
Also, I’d like to propose a new DI story, the life of the user Radiatidon. It seems he’s been to many an interesting place and been involved in a number of interesting events… Who is this mysterious guy/girl?
Doh – before anyone corrects me I meant to type OSI reference model not TCP / IP which classes four layers!
Thanks for all the new Acronyms. I’m going to be busy till the end of the year trying them all out! I’ll do my best to roll on the floor where appropriate :) Thanks to DI I no longer feel left out of the texting generation. It’s funny how culture evolves. Food evolves, fashions evolve, language evolves, technology evolves. It’s in some ways similar to how these crabs evolved. We can get all excited about the Maclear’s rat, and I wonder are we the same people who get excited about a rare old record, or saving VHS tapes from extinction, while listening to cassettes and opt for the vintage feel of stop and rewind as opposed to the ease of a CD?
Evolution in action! Both ecologically and linguistically!
I, for one, welcome our new Masters. May death come swifty to their enemies!
I watched a lot of the National Geographic shows for a while when I was a little kid and would subsequently become afraid of whatever creature or phenomenon was featured. It wasn’t too long after the Black Friday Tornado in Alberta, so I guess I thought natural disasters were a regular occurence in life. My big sister assured me that if the killer bees got past the volcano that I was sure would sprout in the prairie behind our house, then they would definitely get eaten up by all the black widow spiders lurking in our attic. Gotta love big sisters!
FUBAR! My favorite military acronym
Yay for comment implosion! Here it is in its entirity (sans the part what caused the implosion)
“FUBAR! My favorite military acronym! What do all those other ones mean, though? I’ve heard snafu, but never knew it was an acronym…
Oh, and the picture that comes to mind when we’re talking Crabs vs Yellow Crazy Ants is a Godzilla-style movie poster of two giant ones fighting. Ha ha
Can’t believe no one came back with Laughing My Ants Off [no doubt what some Christmas Islanders wish they could do from time to time].
A D.I. and disturbing article, definitely need to break out the ropinirole tonight…
Reaper – SNAFU is one of my favourites. “Situation Normal, All F…ed Up”. It manages to convey a sense of resignation that things aren’t likely to improve. I don’t know what WETSU and DILLIGAF mean though.
Arbuthnot – Thanks for the correction. Now I just need to Google “OSI reference model” :-)
Oh, and another couple of acronyms you may see online:-
JFGI – Just F…ing Google It
RTFM – Read The F…ing Manual.
Why do I know all the ones with “F…ing” in them?
I JFGI’d the last 2 military acronyms…
The best ever is BOHICA!
Bend Over Here It Comes Again!
This is from the enlisted side of the house.
OK, two questions: did you perhaps mean “ten-legged” protagonists (the crabs)?
And I thought I was picky!
I’m no expert on arthropod anatomy, but “eight-legged” seems more than reasonable to me. Crabs have 5 pairs of limbs but the front pair are usually adapted as claws. Seeing as they mostly walk with only 8 of their 10 ‘legs’ I’m happy with eight-legged. I guess technically (biologically?) speaking, I’m typing this with my [heavily-adapted] forelegs but we don’t talk about humans as being four-legged…
So if genetic diversity is the reason for super colonies, just give them more ants to compete with. That is, throw in more yellow crazies. Would be ironic to solve the problem of huge ant populations by adding more ants instead of killing them off. Although, one may have to nuke the current super colonies until the new genetic pools could swell and break ground themselves. Sort’ve level the playing field.
Crab Juice is still better than Mountain Dew…
Speaking of military acronyms, many people don’t know that US ARMY actually stands for Uncle Sam Aint Released Me Yet :P
That’s like crab nightclubb’n. Nice pics.
JIC u missed it…
ROFL LMAO LOL AFAIK IMHO IDK ROFLMAO GTFO MMO BRB WB LSHINTSMKTKFPIMP L8R CYA FUBAR SNAFU WETSU DILLIGAF MILTDD-41 PEBKAC IDtenT OSI TCP/IP JFGI RTFM BOHICA USARMY
I know some crazy yellow ppl btw.
IIRC, iirc stands for “if I recall correctly”. “gg” is usually “good game”, very common in FPS’s. g2g is “got to go”, similar to cya, ttyl (talk to you later), or pc (peace). Acronyms and abbreviations ftw (for the win)!
Did you know they also have birds called “Booby”?
Not to metion the creepy Coconut crab. The largest land-living crab on earth. It clims trees and crack open coconuts! And it’s blue.
It’s just scary…
I think the crab people have a good chance of taking over the world.
God, that would creep me out. I have a thing against bugs and buglike creatures (OCD, on my part). That would be one long panic attack.
We’ve got black ants at our place -which at first I thought, had somehow learned to swim (as we used to have similar looking ants before which couldn’t swim). After googling it I found that it is acutally a new species called polyrhachis sokolova which usually nests in mangroves… how they came to live in our bathroom Ill probably never know… So, yup they’re definetly taking over! O-o