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Mozambique Diary: Coconut crabs of Vamizi

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The coconut crab (Birgus latro), the coolest, most awesome, most beautiful inhabitant of the Vamizi Island. These animals have adapted to live around humans and the conservation group on the island does a good job of protecting them.

In July 1937 Amelia Earhart’s plane vanished somewhere over the southern Pacific in the general vicinity of New Guinea. Neither the plane nor her and her co-pilot’s bodies were found during the massive search operation that followed. But two years after her disappearance scattered skeletal remains, later identified as those of a tall woman of European descent, were found on the (then) desert island of Nikumaroro, one of the possible crash sites of Earhart’ aircraft. The skeleton was far from complete and many bones were missing, and the suspicion immediately fell on coconut crabs, common on the island. They were accused of carrying the bones and squirreling them away. But recently a group of history buffs called TIGHAR came to the crustaceans’ defense, claiming that these animals did not customarily carry away food into their burrows. They even conducted an experiment by placing a pig carcass on the beach of Nikumaroro and recorded a fascinating time lapse video of the crabs stripping it of its flesh. Crucially, though, no bones were carried away by the coconut crabs. But it still showed very convincingly that, had the crabs found Amelia Earhart’s body, they would have eaten her completely in a matter of days. I certainly find this explanation far more compelling and easier to think about than the alternative proposed by the authors of the pig experiment – that her body was eaten not by the crabs but by her starving co-pilot who might have survived the crash. Why the hell would he ever resort to cannibalism on an island full of large, delicious crustaceans and coconuts? (And what happened to him? Two years after the crash people arrived on the island and, if movies are any indication, they should have found a muscular demigod who had a meaningful relationship with a volleyball.)

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Coconut crabs prefer to be active at night and during the dusk. That is when they emerge from their burrows to look for food.

These thoughts ran through my head as I squeezed it into holes in the rugged karst rocks of Vamizi, an island off the coast of northern Mozambique, looking for coconut crabs. Their burrows turned out to be full of coconut shells and other food remains, indicating that a single experiment good science makes not. I had been dreaming of visiting Vamizi ever since my friend Harith showed me a cell phone photo of himself on the island, holding two coconut crabs. All my life I had been fascinated with those magnificent creatures, the largest, heaviest, most awesome of invertebrates that grace the terrestrial surface of the planet. Some years ago I was lucky enough to see these animals alive, first on Guadalcanal, later on Japan’s Okinawa Island, but in both cases they were individuals already captured by somebody else. In those places coconut crabs are on the brink of disappearance due to habitat loss and overharvesting, and I never had a chance to observe them in their natural habitat. Vamizi, however, a tiny speck of paradise in the Quirimbas Archipelago, still appears to have a healthy population of these animals.

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Coconut crabs come in two main color forms, a blue and a red one, both of which can be found in the same population.

Coconut crabs survive on Vamizi thanks to a clever campaign developed by the good people of the Vamizi Marine Conservation Research Centre. If, they say to the locals who traditionally used to hunt the crabs, you kill one, a terrible spell will never let you leave the island. In a country that is full of many ridiculous colorful myths, this scary thought has apparently kept many from falling to the temptation of the coconut crab’s meat. How many crabs survive on the island is unknown but apparently during the wet season it is possible to see a dozen or more coconut crabs on a single stroll through the coastal woodland.

I arrived on Vamizi in June, during the cool, dry season, and the locals were not too optimistic about my chances of finding one. (“They sleep now.”) But I didn’t fly to northern Mozambique on the thieving (camera gear was stolen from our checked-in luggage) and occasionally suicidal LAM airlines (go ahead, google it) to leave without seeing a coconut crab. According to Harith the best chance of finding one would be at a place that reliably provides the crabs with their favorite food. No, not coconuts. They prefer something else – fresh garbage.

“Take me to the dump”, I asked Harith as soon as it started getting dark. As we approached the island’s refuse disposal site we heard a sound that I would have never associated with coconut crabs – loud clicking of empty bottles. And there they were. Two giant, surprisingly colorful animals, moving among a big pile of glass, looking for edible bits of organic matter. The setting was not natural, it certainly wasn’t beautiful, but I almost choked up when I saw them. It was at the same time a fulfillment of a life-long dream, to see coconut crabs in the wild, and a sad, disappointing realization that “wild” is a big pile of junk and rubbish, reeking of rotten food and overrun by rats. The Anthropocene, in its full splendor and glory.

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The Anthropocene – is this what a “wild” habitat should be?

Over the next few days my outlook had improved as I counted and photographed the crabs, looking for an indication that the population was breeding on the island. A large part of the island is a well-protected nature reserve, full of gorgeous tropical life, including thousands of land crustaceans, small mammals, breathtaking birds, and cool reptiles (including two species new to science, which Harith will soon be describing.) And I won’t even mention the marine life, which puts Vamizi at the top of the list of the most spectacular diving sites of the world. The most reliable proof of the crabs breeding there would have been finding juveniles still in their shells. Coconut crabs (Birgus latro) are oversized, fully terrestrial hermit crabs, that, just like other members of the hermit crab family Coenobitidae, develop as microscopic planktonic larvae in the ocean, and must don an empty snail shell during the first months of their life on land to protect the still soft and fragile abdomen. Only after reaching the size of about 10 mm do they abandon the shell and assume the symmetrical appearance that differentiates them from other hermits (in all other species the abdomen remains asymmetrically twisted throughout their life.)

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Coconut crabs are excellent climbers. Also known as robber crabs, they are known to raid bird nests.

I must have picked up and examined about a thousand hermit crabs but, alas, they all turned out to be one of the two local species of Coenobita. A trip to a coconut grove at the opposite end of the island to look for juveniles hiding in the fallen fronds and coconut husks underneath the palm trees was similarly fruitless. That was worrisome. Rats are known to kill juvenile coconut crabs and the island was full of them. We saw rats not only around the houses but also in the most remote, virtually unspoiled natural habitats of Vamizi. One night my friend Max was startled by a gecko that hurled itself towards his head from the very top of a tall tree to escape a rat chasing it on the thin branches. Adult coconut crabs can and will kill a rat, but younger ones don’t stand a chance. Thankfully, the tourism company &Beyond, which operates the phenomenal eco-resort on the island, has been working diligently to improve the situation. To remove invasive species from Vamizi without harming its native populations of samango monkeys and other small mammals they use specially designed rat-only traps, ultrasonic repellents, and other tools to get rid of the nasty aliens.

Every night I spent hours looking for juvenile crabs along the paths in the forest but all I was seeing were very mature adults. On the last night, dispirited by not finding any proof of new blood in the population, I walked further than usual and ended up being out in the field well past 2 AM. Tired and despondent, I decided to have one last tour of the resort staff houses, the most reliable spot for finding coconut crabs at that time of year. There were a few adults milling around but they soon left for their burrows in the forest. That was it. During my four days on the island I did not see any evidence that the animals were breeding. A similar pattern has been seen in other places inhabited by coconut crabs, where the pressure from invasive species, overharvesting, and habitat loss either prevents the animals from breeding or leads to unnaturally high mortality of juveniles. Despite coconut crabs’ longevity (they can live to be 60), with no young crabs surviving the population eventually dies out.

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All I can say is that I am glad that I am taller than a coconut crab (albeit not by much!)

I swept the light of my headlamp around, noticing for the first time the fence at the far end of the compound, overgrown with tall, spiky weeds. It occurred to me that I had never checked what lived among them. If I were a young coconut crab, would I want to compete with the adults, and risk being eaten, by feeding at the same spot, at the same time of night? I climbed the fence and crawled through the thicket, long, thorny branches ripping my shirt and cutting my skin. The ground below the weeds was covered with Coenobita hermit crabs, frantically gorging on discarded scraps of food. And there, among the hermits, were the juvenile coconut crabs. They weren’t much bigger than the large hermit crabs C. brevimanus common on the island, about 5-7 cm long. I let out a sigh of relief. The presence of young coconut crabs made it clear that the population was thriving, or at least not dying out. And the help they get from the conservation group working on the island will certainly improve their chances.

The next morning Harith, Max, and I left the island, having learned not only that it had a good population of coconut crabs, but also that eating oysters directly off the sun baked rocks exposed by the low tide really helps you purge your digestive system. I hope to go back to Vamizi sometime soon and do a more thorough assessment of the crabs’ population. And if I ever perish somewhere near to where these gorgeous animals live, I hope that they find me.

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The underside of a blue coconut crab.

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The edge of the underside of a coconut crab’s thorax looks very reptilian.

Mozambique Diary: Photoshop or not?

Rock scorpion (Hadogenes granulatus) from Bunga Inselberg in Gorongosa, one of the largest scorpions in the world.

Rock scorpion (Hadogenes granulatus) from Bunga Inselberg in Gorongosa, one of the largest scorpions in the world.

One of the more entertaining consequences of posting images of obscure, rarely seen animals on this blog or on my Facebook page is that I am sometimes accused of faking them, especially if a Google search by those who doubted the veracity of my photos did not produce similar pictures taken by other photographers. This happens particularly often with animals that are the largest of their kind, be it a giant land crab or, more recently, a parasitic bat fly. I wonder if the photos in this post will be met with similar incredulity.

Bunga Inselbergs in Gorongosa National Park, Mozambique

Bunga Inselbergs in Gorongosa National Park, Mozambique

Last month I lead (lured) a group of researchers to a remote corner of Gorongosa National Park to continue the documentation of the biological richness of this remarkable place. Our camp was at the foothills of the Bunga inselberg, one of several small, isolated mountains in the western part of the park. These inselbergs have never been biologically explored and although we did not expect to find any endemic species there was always a chance of encountering rare or new to science organisms. These inselbergs are, in an essence, giant piles of volcanic rock, covered with a very thin layer of topsoil and a dense carpet of woody vegetation. Such a habitat is heaven for a lot of animals but, to my great relief, not lions and elephants. This meant that we could roam freely around the inselbergs in a relative safety, not constrained by the need to be always accompanied by armed park rangers. I say “relative” because Africa is rich in things that can get you, and Bunga inselbergs were no different – on my first visit there my friends and I were attacked by a cloud of wild honey bees, and on the following day I pulled nearly 150 stingers from my arms and neck. (It was a close call – I remember thinking “At least this is the end fit for an entomologist,” before losing consciousness.) Thankfully there were no similar incidents during this survey, although I did make sure that every person carried an Epipen kit to treat potential anaphylactic shock.

The median ocelli of the rock scorpion (Hadogenes granulatus) are protected from scratching against rocks by elevated ridges (green arrow). These are absent in species that live in equally constrained but softer environments, such as this Opistacanthus (below) found under tree bark.

The median ocelli of the rock scorpion (Hadogenes granulatus) are protected from scratching against rocks by elevated ridges (green arrow). These are absent in species that live in equally constrained but softer environments, such as this Opistacanthus (below) found under tree bark.

Lifting heavy volcanic rocks to look for animals during the survey was hard work, but it was also immensely rewarding. Each flat piece of basalt could have been hiding a cool gecko, a snake, a family of crickets, some awesome beetles, or a scorpion, and it was the last one that gave me the biggest surprise. Rock scorpions of the genus Hadogenes are considered the largest, or at least the longest, scorpions in the world. Some species can reach the length of 22 cm and several individuals from Bunga were at least this big. Granted, a large portion of the body is the long and thin telson (“tail”) of the animal, but it is still a spectacular beast, which will make you pause when you see it scurrying around your fingers. All species of Hadogenes are obligate lithophiles; in other words, they love rocks. Their bodies are perfectly adapted to squeezing into narrow crevices, and their feet carry stiff setae and strongly curved claws that allow them to cling to even the smoothest rocks (and hang from rocks upside down, something that few other scorpions can do). Their median ocelli – the main pair of eyes – are protected by elevated ridges that prevent them from scratching against the rocks, and the entire body is flatter than in any other scorpion of similar size.

Like many scorpions, members of the genus Hadogenes display a beautiful, blue fluorescence if exposed to ultraviolet light. A recent study suggests that this helps these nocturnal animals detect and avoid light.

Like many scorpions, members of the genus Hadogenes display a beautiful, blue fluorescence if exposed to ultraviolet light. A recent study suggests that this helps these nocturnal animals detect and avoid light.

But, as it is often the case, a large size and a scary appearance do not necessarily translate into true ability to inflict harm. The giveaway is the telson, which in rock scorpions is long and thin, betraying the presence of weak muscles and a small venom gland, and thus the lack of reliance on venom for capturing prey and defense. They can and do sting, of course, but the strength of their venom is no greater than that of a bee (and, thankfully, scorpions do not move in large swarms and are far more friendly than those pissy little bits of flying pain). A few species of Hadogenes have the ability to spray venom towards the attacker, which can cause painful irritation if the droplets get into your eyes, but otherwise they are harmless. In fact, an article (pdf) describing the medical importance of rock scorpions puts more emphasis on their ability to pinch your fingers then to envenomate.

Scorpions of the genus Hadogenes occur in rocky habitats across southern and East Africa, often on isolated mountains, leading to frequent allopatric speciation and a high number of endemic species. When I first found rock scorpions on Bunga I was hoping for a new, undescribed species but, alas, this turned out not to be the case as they were all members of H. granulatus, a species known from other places in Mozambique.

I photographed one of the individuals sitting on a vertical rock next to my hand. I knew that the animal was pretty harmless but I still was not looking forward to comparing its venom to that of a bee, and decided not to shoot it sitting directly on my hand. And, of course, it made it much easier to manipulate the image in Photoshop to make the scorpion appear bigger. (Kidding!)

Rock scorpions’s body is strongly flattened, perfectly adapted to squeezing into the narrowest crevices.

Rock scorpions’s body is strongly flattened, perfectly adapted to squeezing into the narrowest of crevices.


Flavio Artur, Ricardo Guta, and I, 24 hours after being attacked by a swarm of wild African honey bees. On that morning I pulled out nearly 150 stingers from my skin.

Flavio Artur, Ricardo Guta, and I, 24 hours after being attacked by a swarm of wild African honey bees. On that morning I pulled out nearly 150 stingers from my skin.

 

Mozambique Diary: How to kill an assassin

The African assassin bug (Glymmatophora sp.) from Gorongosa, Mozambique

The African assassin bug (Glymmatophora sp.) from Gorongosa, Mozambique

I often lament the fact that humans are freakishly gargantuan next to nearly all other animals, and thus unable to appreciate the beauty and complexity of the majority of smaller life forms that share the world with us. Yet, at the same time I am thankful that we do not need to contend with the likes of tiger beetles or solifugids, and that ambush bugs will never succeed in luring us into their deadly grip with their imitation of the sounds that humans make. Compared to even the most vicious and dangerous mammals, the world of arthropods is orders of magnitude more advanced in the art of killing – if a lion were to be shrunk to the size of an average insect it would last no more than a few minutes before being dismembered by the first praying mantis or a spider, who would laugh at its puny claws, soft and squishy body, and the complete lack of any real weapons.

The hunt begins –the assassin bug notices the millepede and begins to approach it.

The hunt begins –the assassin bug notices the millepede and begins to approach it.

And although I prefer to study the more peaceful aspects of invertebrate behavior, such as their courtship and love songs, I cannot help but be impressed by the sophistication of weaponry used by arthropods to kill, or exact revenge on those who try.

On my last night in Mozambique, when I should have been packing and getting some sleep before a long journey home, I suddenly realized that I had almost missed the opportunity to solve the mystery of how ectrichodiine assassin bugs hunt their favorite prey, the giant African millipedes. I had caught a beautifully metallic, wingless assassin bug (Glymmatophora sp.) a few days earlier, and now all I needed was its prey. Luckily, I was still in Gorongosa, where most biological questions can be answered by taking a slow walk and paying attention, and within a few minutes I managed to find a large millipede.

Without the millepede being aware of it, the assassin bug slowly crawls on top.

Without the millepede being aware of it, the assassin bug slowly crawls on top.

For a docile, seemingly harmless animal, millipedes (Diplopoda) have surprisingly few enemies. As is often the case among small animals, an innocent demeanor hides powerful and quite unexpected defensive strategies. Millipedes have two major lines of defense, both effective enough to deter virtually all predators. First, the chitinous base of their exoskeleton is composed of up to 70 percent calcium and magnesium carbonate, making it much harder than that of most terrestrial arthropods. Few predators are strong enough to crack it, although mongooses have been reported to toss  millipedes against rocks to break their shells. For smaller predators such as spiders, the hard exoskeleton is an almost impenetrable barrier. But if one tries its luck anyway, a rich arsenal of chemical warfare stops the predator in its tracks, literally. Some millipedes produce substances that act as sedatives, forcing the spider into a state of suspended animation that lasts for many hours. Interestingly, this substance is virtually identical to the drug quaalude, a synthetic sedative once widely used in medicine and as a recreational drug. But licking millipedes to get high is not a good idea as many species produce cyanide, the most powerful inorganic poison known to man.

The assassin bug positions itself so that its rostrum can be inserted between the millepede's legs.

The assassin bug positions itself so that its rostrum can be inserted between the millepede’s legs.

Others exude substances that cause vomiting, headaches, and other unpleasant effects. And yet, few millipede species have warning coloration, which is typical of organisms that produce repellant chemicals. It is believed that the extreme effectiveness of their chemical weapons, combined with the very long time they have been around (terrestrial millipedes date back to the Carboniferous), made predators develop a genetically based aversion to these animals, and the millipede’s shape alone is a sufficient warning.

Once in place, the assassin bug delivers the deadly bite.

Once in place, the assassin bug delivers the deadly bite.

Assassin bugs (Reduviidae: Ectrichodiinae) are some of the very few animals that are able to hunt millipedes. They overcome the millipedes’ mechanical defenses by injecting them with a fast acting venom through a soft membrane between the calcified plates that cover their body. They also avoid being poisoned by their prey’s chemical defenses thanks to the way they feed – rather than chewing food, and thus potentially ingesting some of the toxic compounds, they inject their prey with digestive enzymes and then drink the liquified tissue through a long, sharp rostrum. All this is well known to biologists, of course, but surprisingly there exist very few documented observations of how the hunt unfolds, and what part of the millipede’s body is targeted by the assassin bug. On my last night in Gorongosa I had a chance to find out.

The assassin bug's bite makes the millipede convulse and exude yellow droplets of toxic benzoquinones.

The assassin bug’s bite makes the millipede convulse and exude yellow droplets of toxic benzoquinones.

I placed the two animals on the white stage of my field photo studio and waited. After a few minutes the assassin bug noticed the millipede and started to approach it stealthily. With imperceptibly slow steps it climbed the millipede’s body and positioned itself almost upside down, with the head and rostrum facing the ventral side between the millipede’s legs. It was clearly aiming for the softest part of the body. And then, with an amazing speed, it pierced the millipede with its stiletto-like rostrum. The millipede’s reaction was dramatic – its body twisted and uncoiled like a spring, nearly sending it up into the air. After a few seconds the body relaxed, and yellow, acrid droplets started oozing from between its plates. This was the moment when the assassin bug decided to walk away.

After a few minutes the millipede is dead (but read the entire story to see what happened next).

After a few minutes the millipede is dead (but read the entire story to see what happened next).

I was already feeling bad for staging this drama, but the bug’s behavior made me feel even more guilty. “You ain’t going nowhere, buddy”, I thought as I placed a large container over the predator and its prey, “finish the job and eat it.” I simply could not understand why the assassin bug, which clearly must have been hungry, would suddenly abandon its dinner. And then, within a couple of minutes, the assassin bug was dead.

It all now made sense – the assassin bug was not abandoning its kill, it was just walking away to avoid being poisoned by the deadly benzoquinones dripping from the body of its victim. It would have undoubtedly come back to feed after the millipede had died and most of the volatile chemicals had blown away. By placing a container over the two animals I created a gas chamber that killed them both. I still feel awful about it but, alas, this is how biological mysteries are sometimes solved. I strongly suspect that the scent of benzoquinones, which are only emitted by an injured or dying millipede, acts as a long-range attractant to other assassin bugs that are often seen feeding communally on large millipedes, but at the same time the animal that made the kill must temporarily move away to avoid death from the same compounds. Aren’t invertebrates amazing?

The Greatest Show on Earth, happening now

The best time to see Atlantic horseshoe crabs (Limulus polyphemus) is on the nights of the full and new moon in May and June.

The best time to see Atlantic horseshoe crabs (Limulus polyphemus) is on the nights of the full and new moon in May and June.

I am still in Mozambique, and will be here for a few more weeks, but I simply must take a quick break from describing African nature to highlight a spectacular phenomenon that is taking place right now along the eastern coast of North America – the mass spawning of the Atlantic horseshoe crabs (Limulus polyphemus). Watching these magnificent animals is to me one of the most beautiful natural events that one can witness, and I encourage everybody living on the East Coast to take a trip to the beach this and next month (this year the best time to see them are nights of May 24th, and June 9th and 23rd.) What follows is a short excerpt from my book “Relics” (Chicago University Press 2011), describing my experience of watching horseshoe crabs on the beaches of the Delaware Bay.

“As hundreds of biting flies did their best to drain us of every drop of blood, my friend and fellow photographer Joe Warfel and I stood on the beach, waiting for the spectacle to begin. The sun grew dim, and the high tide was nearing its peak. There were a few people on the beach when we first arrived, but by now they had all disappeared, and we were the only witnesses to what was about to unfold. I started to tell Joe how strange it was that nobody else stayed to watch, but swallowed a fly and decided to quietly enjoy the rest of the evening. First came the big females. Nearly all had males in tow. In the dimming light we could see spiky tails of hundreds more as they tumbled in the waves, trying to get to the dry land. By the time the sun fully set, the beach was covered with hundreds of glistening, enormous animals. Females dug in the sand, making holes to deposit their eggs, nearly 4,000 in a single nest, while the males fought for the privilege of fathering the embryos. Fertilization in horseshoe crabs is external, and often multiple males share the fatherhood of a single clutch. Equipped with a pair of big, compound eyes (plus eight smaller ones), capable of seeing the ultraviolet range of the light spectrum, male horseshoe crabs are very good at locating females even in the melee of waves, sand, and hundreds of other males.

Delaware Bay is the best place in the world to see these magnificent animals. On a good night one could easily see 100,000 horseshoe crabs.

Delaware Bay is the best place in the world to see these magnificent animals. On a good night one could easily see 100,000 horseshoe crabs.

Horseshoe crabs have been around longer than most groups of organisms that surround us now. A recent discovery in the fossil deposits of Manitoba, an interesting little creature named Lunataspis aurora, proves that horseshoe crabs quite similar to modern forms were already present in the Ordovician, 445 million years ago. By the time the first dinosaurs started terrorizing the land in the Triassic (about 245 million years ago), horseshoe crabs were already relics of a long-gone era. And yet they persisted. Dinosaurs came and went, the Earth changed its polarity and climate many times over, but horseshoe crabs slowly plowed forward. Yet during this time they changed surprisingly little. Species from the Jurassic were so similar to modern forms that I doubt I would notice anything unusual if one crawled in front of me on the beach in Delaware. Somehow horseshoe crabs had stumbled upon a lifestyle and morphology so successful that they were able to weather changes to our planet that wiped out thousands of seemingly more imposing lineages (dinosaurs and trilobites immediately come to mind.) But despite claims to the contrary by creationists and other lunatics, they kept evolving. Modern horseshoe crabs, limited to three species in Southeast Asia and one in eastern North America, differ in many details from their fossil relatives. We know, for example, that many, if not most of fossil horseshoe crabs lived in freshwater, often in shallow swamps overgrown with dense vegetation, and some might have even been almost entirely terrestrial. Currently only the mangrove horseshoe crab Carcinoscorpius rotundicauda from the Malayan Peninsula routinely enters rivers, and is the only species to lay eggs in fresh or brackish water.

Even Sir David Attenborough, the man who probably witnessed more natural spectacles than any other human being, is fascinated by the spawning of horseshoe crabs. Here he demonstrates the improper way of holding a horseshoe crab (never hold them by their telson) while on the beach in Delaware during the filming of the BBC series "Life in the Undergrowth".

Even Sir David Attenborough, a man who probably witnessed more natural spectacles than any other human being, is fascinated by the spawning of horseshoe crabs. Here he demonstrates the improper way of holding a horseshoe crab (never hold them by their telson) while on the beach in Delaware during the filming of the BBC series “Life in the Undergrowth”.

The following morning Joe and I found the beach covered with horseshoe crab eggs. Well-rested and ready to start a bright new day the flesh-piercing flies attacked us with a renewed enthusiasm. Flailing our arms and swatting dozens at a time we went about flipping crabs stuck on their backs in the sand, and started to look for particularly big clutches of eggs. Although females burry the eggs in the sand, the returning tide washes out many of them. Freshly laid eggs are small, not larger then half a grain of rice. Surprisingly, the eggs grow as they develop, eventually becoming more than twice as large. This, of course, is impossible. The “growth” is an illusion, the result of the production of an external, thin membrane by the developing embryo. A fully developed egg, which at this stage has spent two weeks in the sand, resembles a tiny glass aquarium, with a petite horseshoe crab twirling inside, impatient to break the walls of its miniature prison. Once free, the larva (or at least the lucky ones) catches a wave back into the ocean and will spend about a week floating freely, before settling on the bottom of the shallow shore waters to begin life akin to that of its parents.[…]”

Tiny horseshoe crab larvae, known as the trilobite larvae, twirling in their aquarium-like egg shells. Soon they will break free to begin a short pelagic period, after which they settle on the bottom of the ocean to begin a lifestyle similar to that of their parents.

Tiny horseshoe crab larvae, known as the trilobite larvae, twirling in their aquarium-like egg shells. Soon they will break free to begin a short pelagic period, after which they settle on the bottom of the ocean to begin a lifestyle similar to that of their parents.

Just like their distant relatives, scorpions, horseshoe crabs display green fluorescence under the ultraviolet light.

Just like their distant relatives, scorpions, horseshoe crabs display green fluorescence under the ultraviolet light.

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Atlantic horseshoe crabs on the Prime Hook Beach near Milford, Delaware.

Our top predator

House centipedes (Scutigera coleoptrata) are born with only 4 pairs of legs, but eventually develop 15 pairs [Canon 7D, Canon 100mm macro, 3 x 580EXII]

As the days grow shorter and colder, I find myself paying more and more attention to the organisms that I took for granted throughout the entire summer. Suddenly, cricket songs punctuate the unexpectedly chilly nights with hesitation, moths coming to the light on our deck are getting smaller and rarer, and spindly centipedes trapped in the kitchen sink in the morning remind me that I should count my arthropod blessings before winter takes most of them away.

The house centipede (Scutigera coleoptrata) is a particularly welcomed inhabitant of my domestic ecosystem. I have always been fascinated by these animals, and one of my life’s greatest achievements was the ability to convince my wife, who would rather be in the same room with a wild grizzly than a 3 mm long spider, to tolerate and (almost) appreciate their presence. On a few occasions a large centipede ran across the carpet in the living room while we watched TV, and Kristin didn’t bat an eye. (Perhaps 8 legs is that magical number that triggers irrational fear in some people – fewer than or more than 4 pairs is simply not perceived as threatening or creepy, at least not as much.)

House centipede with a cockroach prey; notice the large fangs (forcipules), which deliver the venom that kills the victim, and a prehensile foot holding the cockroach’s leg. [Canon 7D, Canon 100mm macro, 3 x 580EXII]

House centipedes came to North America from the warm, Mediterranean region of Europe, where they can be found in caves and other shady, humid environments. In New England and other places with harsh winters they prefer to spend at least part of the year in houses, and live outside only during warmer summer months. This is why people generally start noticing them in the spring, when these animals look for ways to get out of the house, and then again in the fall, when they come back to spend the winter in the safety of our basements. Their presence in people’s homes is a reminder of the fact that houses are, in an essence, caves inhabited by large mammals. These mammals provide a constant stream of organic debris, which in turn supports a rich fauna of prey species for the centipedes: mites, silverfish, flies, and cockroaches, to name a few of our troglophiles.

Centipedes are the top predators of our domestic ecosystems. They are the equivalent of cheetahs in the African savanna – lean and long-legged chasers of those who scavenge our organic refuse, catching their prey and immediately killing it with one powerful bite. But their weaponry is even more sophisticated than that of the cats. Since the nervous system of insects is not as centralized as that of mammals, crushing the head of the prey would not necessarily kill it. A far more effective method is to inject the prey with venom, which instantly paralyzes it and stops it from struggling. Centipedes do so with a pair of modified legs, shaped like a pair of fangs and connected to venom glands. (Be not afraid, however – these are not capable of piercing our skin, in the unlikely event that you caught one of these things and forced it to bite you; centipedes have absolutely not interest, or capacity, to attack people.)
They also have something else that cheetahs lack – prehensile legs that can wrap around the appendages of their prey, in a way remarkably similar to that in which an octopus handles its victims. Having 15 pairs of long, grasping legs allows centipedes to carry their prey, and even hold one while hunting for another.

If you have seen these animals around your house, count yourself lucky. Their presence assures that no pest species will be able to multiply unchecked, and spread harmful germs from your trash and pipes into the rest of the house. Centipedes may not be the cuddliest of your roommates, but they pay their rent and keep the house clean.

House centipede with a cockroach prey [Canon 7D, Canon 100mm macro, 3 x 580EXII]

Galapagos: A most unexpected find

Velvet worms have a round mouth opening, and a pair of glands on both sides that shoot sticky strands used to entangle their prey [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]

Like virtually all geologically young, small oceanic islands and archipelagos of volcanic origin, the Galapagos should not have certain groups of organisms. Neither amphibians, for example, nor freshwater crabs are found in such places. This is because these freshwater-dependent organisms are extremely unlikely to survive an oceanic voyage needed to colonize remote islands, and even if they somehow make it across, the chances of finding an appropriate aquatic habitat on the island are virtually null. I was therefore quite surprised, nay, shocked, when I spotted on a trunk of a tree in the middle of Santa Cruz island a small velvet worm. Then another one, then another, and two more, and fifteen additional ones. The place was crawling with them.

How could that be? Let’s begin with the fact that velvet worms, members of the somewhat enigmatic phylum Onychophora, are notoriously difficult to find. In my 20+ years of working in the tropical areas of the world I can count on the fingers of one hand all the velvet worms I have ever seen. These animals are also tied to highly humid habitats, and apparently (although I could not verify this information) they will die if the air humidity around them drops below 80% – these are seriously humid conditions. Clearly, an animal like this is very unlikely to be able to colonize remote volcanic islands. And yet, there they were, and plenty of them.

As you might suspect, they are a very recent arrival to the Galapagos. They were first spotted in 1992, most likely brought inadvertently with a shipment of bananas from South America. From the shipping docks of Puerto Ayora they have spread to higher, more humid areas of Santa Cruz, and flourished ever since. Their high abundance can be explained by the fact that the Galapagos lack most of their natural enemies; centipedes in particular, their main predators in places where velvet worms naturally occur, are rare in the archipelago. Velvet worms are themselves hunters of small invertebrates, and where I found them, in a humid forest of Santa Cruz, schizomids (tiny arachnids, also introduced) and small isopod crustaceans were plentiful. Based on the photos I took I was able to place the Galapagos velvet worms in the genus Oroperipatus of the family Peripatidae, which indicates that they must have arrived from somewhere in South America north of Chile (which has members of a different velvet worm family, the Gondwanan Peripatopsidae.) It will be interesting to see if they manage to colonize other islands of the archipelago in the coming years.

Velvet worm (Oroperipatus sp.) from Santa Cruz [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]