When the earliest dinosaurs were first evolving around 230 million years ago, horseshoe crabs had already been scuttling along the ocean floor feeding on marine worms and tiny shellfish for at least 100 to 200 million years; maybe even longer. Today, they still remain relatively unchanged—‘living fossils’ that have survived at least 5 mass extinctions throughout the eons and outlived most of their closest relatives, such as the ancient trilobites, whose famous fossils can be seen in museums throughout the world. Perhaps the term “lucky horseshoes” should really pertain to these amazing little creatures who are one of the oldest species on earth.
As a native of New Jersey, I hold a special place in my heart for these unusual animals. Every summer throughout the months of May and June, they arrive in large numbers along the beaches, most famously in the Delaware Bay, to spawn. I like to walk down the shoreline in the early morning to look for them; every now and then helping to right those that had been flipped upside-down by the surf. Since it is currently the peak of their breeding season, I figured I’d write a little bit about them for anyone who has never had the chance to see one in person.
First, I should point out that horseshoe crabs are not really crabs or even considered ‘crustaceans,’ at all. They are actually more closely related evolutionarily to spiders and scorpions, than crabs, lobsters, or shrimp. Millions of years ago, there were many different kinds of horseshoe crabs, though today only four species remain. Limulus polyphemus, is the species that we see most commonly on the eastern shores of North America and in the Gulf of Mexico, but other species can be found from the shores of India to Sumatra, Java, the Philippines, and China when they come ashore to breed.
All horseshoe crab species have the same general shape, with bodies made up of three sections covered by hard armor-like plating; some can even grow up to 3 feet long. The first and largest section resembles a semi-circle or horseshoe-shape, called the prosoma (I like to call this the head). Looking down at the animal from above, this section contains two large compound eyes on each side, but there are also 5 other rudimentary ‘eyes’ that are much smaller and harder to see. Some are sensitive to visible light, while others are sensitive to the ultraviolet range. It is believed that horseshoe crabs see very well at night, and also pick up on contrast better than we can, but this has not been verified.
If you turn the crab over to see the bottom of the prosoma, there are five pairs of legs—the pair closest to the tail of the animal are modified ‘pusher’ legs that they use to propel themselves with, and to clean their gills. Each leg, save for the pusher legs, have pincers at the end. In females, all these pincers look the same, but in males, their forward-most legs, called the pedipalps, are rounded with a little hook on the end that many researchers refer to as ‘boxing gloves.’ These help them hold onto the female’s shell during mating. Females also tend to be much larger than males, which is another way to tell them apart.
There are an additional two tiny legs in front of the others called chelicerae, which help push food towards the mouth, which is located between the five sets of main legs. The mouth structure is called a gnathobase, is lined with tiny hair-like spines, and the crab can only swallow food (always whole since it doesn’t chew) if its legs are moving. Spiders, the crab’s distant relatives, also have chelicerae, except they are usually in the form of pointed fang-like appendages that some use to grasp food. They are also often hollow, and/or connected to venom glands. But don’t worry–horseshoe crabs aren’t poisonous at all. They even have two additional light receptors or ‘eyes’ near their mouths, which are believed to help them orient while swimming.
The central section of a horseshoe crab’s body is called the opisthosoma. This is lined with movable spines on each side, and contains the musculature to move the tail as well as the ‘book gills’ underneath. These not only exchange respiratory gasses to allow the crab to breathe, but can also move like a series of fins and can help them swim. In fact, as long as the book gills remain wet, the crab can breathe—hence why they can come out of the water and survive by sitting on the wet sand. They don’t swim often though, usually only if necessary to escape predators like sharks, or to help move in rough surf. When they do, they usually swim upside-down.
The last part is called the telson, which is a fancy name for the tail. Many people think it is a poisonous spine, but this is a common misconception. The horseshoe crab just uses its tail to turn itself right-side up if it gets flipped over. Horseshoe crabs also cannot walk or swim backwards—if one gets cornered or stuck, it must use its tail to flip itself over and swim away. The series of bumps along the top and side of the tail are additional light receptors. Being primarily nocturnal animals, these are very important to help it synchronize with the day and night cycles.
Horseshoe crabs are also relatively long-lived, and it is believed they can survive up to 20 years or more. They grow in stages and molt their shells for about 10 years or so, until they mature. Once fully grown, they stop molting and often gain hitchhikers like mussels or barnacles that begin to grow on them. Each spring, during the high tides of the new and full moon, the males line the shores waiting for the females. Once they arrive, groups of males surround each larger female trying to grab on with their pedipalp. Once one does, he is dragged behind her as she lays up to 20 clutches of eggs in shallow holes that she digs, each clutch containing about 4,000 tiny pastel-green eggs. He fertilizes them as they are laid, and they hatch within 3-4 weeks.
These eggs attract huge numbers of shorebirds every year who gorge themselves with them to bulk up for their long migrations. One of the most famous of these birds has one of the longest migration routes known, and it is called the Red Knot. These small birds fly from the very tip of South America in Tierra del Fuego making a pit stop in Brazil, and then fly nonstop to the Delaware Bay to gorge themselves on eggs to prepare for the last leg of their journey—a nonstop flight to their arctic breeding grounds. Their total journey is about 9,300 miles!
Because horseshoe crabs have been hunted excessively in the last century for fertilizer (their bodies were ground up because they are high in nitrogen), and used as bait, the decline in crab numbers has also caused a decline in the numbers of these birds.The crabs have also been harvested in large numbers since the 1960s and 70s for use in the medical industry. Not only are their eyes being studied, but their blue blood is copper-based and contains an interesting substance called limulus amebocyte lysate (LAL) which can be extracted and used to detect bacterial toxins.
I suppose by writing this post, I just wanted to raise awareness of these amazing and fascinating creatures, as well as urge people to protect them. They have survived for so long, through such extreme conditions, that I find the fact that humans have done so much damage to their populations in such a short amount of time very disheartening. We are making advances though. Crabs are no longer killed for blood collection, but once they are captured, only about 30% of their blood is taken before they are returned to the ocean. Their blood volume rebounds within a week or so, while research has shown that it takes about 2-3 months for their blood cell count to return completely back to normal. In the past, moratoriums have also been placed on the harvest of horseshoe crabs in certain areas.
Finally, I can’t describe how many times I see kids at the beach picking the crabs up by their tails. This can seriously harm the crabs and parents must urge their kids not to do this. In addition, if there are shorebirds feeding on the beach, please do not disturb them. They need to eat as much as they can so they can make it to the arctic.
To learn more about horseshoe crabs and the shorebirds that depend on them, feel free to check out the following links:
Every morning and evening in the Amazon, wild parrots gather on exposed cliffs like this one to engage in geophagy, a fancy word for eating dirt. As the parrots scrape and lick the clay-rich soil, they socialize — loudly. “They’re all screaming their heads off,” says U.C. Davis conservation biologist James Gilardi. The smooth-textured clay, he says, acts like a water softener in the parrots’ guts, helping to neutralize the toxins the birds ingest from eating unripe and even poisonous seeds.
Gilardi studied two parrot “clay-licks” in Peru for his Ph.D thesis, and now runs a conservation organization called the World Parrot Trust. Despite their popularity, parrots remain mysterious in the wild. Geophagy is just one example of a behavior that has been largely overlooked. Gilardi studies wild parrots in the hopes of conserving them in their native habitats and allowing people to take better care of them as pets. This week, his team published new evidence in PLoS ONE showing that parrots seek out bitter, toxic foods other animals won’t touch.
To catch the birds snacking, Gilardi and his team spent several summers walking through Manu National Park in the Peruvian Amazon. They spent up to ten hours per day watching from the ground for parrots rustling in the canopy and listening for squawking cries or the sound of falling fruit. When they found the parrots, they wrote down the kind of tree the birds were in, and noted what dropped on the ground. They also climbed the trees to collect samples, and sat in the canopy watching the birds fly and forage. They wanted to know whether the birds preferred seeds or fruits, how thoroughly they “demolished” their food, as Gilardi puts it, and whether they gobbled up ripe or unripe fruit and seeds. Parrots are messy eaters, but it was soon clear that the birds were going after unripe seeds. Many of these are protected by bitter, potentially toxic substances like alkaloids, found in substances like hemlock and strychnine.
The parrots weren’t just swallowing seeds and pooping them out intact, like many animals do. Instead, they were digesting them. This wasn’t a surprise, says Gilardi. Large macaws can destroy softball-sized seeds with their beaks, cracking shells that would take a monkey many blows with a rock to break apart. “Anyone who’s ever watched parrots in the wild knows that they are destroying seeds.” What surprised him was the toxicity of the seeds they were digesting: “A lot of the things they’re eating are pretty nasty.” Sometimes they would see a tree full of fruit which other birds or animals shunned. Then the parrots would arrive and “just plough through” it.
In addition to detoxifying their systems by eating clay, Gilardi says that parrots’ livers and other aspects of their physiology are better equipped than ours to deal with poisonous substances. Although parrots are one of the most endangered bird species in the world, parrot conservation almost never has anything to do with food. “It’s one less thing to worry about.”
More often the threat is habitat destruction and capture. “Parrots are often threatened by something local to them,” says Gilardi. Parrot trafficking for pet sales, in addition to the clearing of tropical forests, threatens roughly more than one in four parrot species — about 95 out of 360 total. Although the World Parrot Trust doesn’t condemn bird-keeping, it works to protect parrot habitat, eliminate illegal and unsustainable parrot trafficking, and help pet owners care for their birds correctly. “If we’re going to do this,” he says, “let’s do it right.”
People tend to feed parrots things people like to eat: cereal crops that have been heated up, cooked, and shaped into pellets. They feed them ripe fruit when a parrot might actually prefer something as astringent as an unripe persimmon. “It’s a huge problem,” says Gilardi. He hopes that people will consider that their backyards might be a better place to find parrot food than the grocery store.
Photo credit: Wikipedia Commons
This was it—go time. Standing poised but slightly crouched like a football player about to spring into action, our eyes were on the clock. My hands were beginning to sweat within the latex gloves I was wearing and I nervously adjusted my face mask to bide the time.
“Okay guys, here we go,” I heard the surgeon say as my fellow ‘team mates’ stood in line behind me at the ready, and we counted down the seconds in our heads as he did so aloud in front of us. Hey, this was my first time doing something like this after all—and I couldn’t help but be a little nervous, not to mention I had only just been hired. I would NOT mess this up.
Standing at the door of the surgical suite, I looked at the patient. She had been secured upside-down on her back, and was being remarkably well-behaved—luckily for all of us, as it’s not always the case. Her enlarged abdomen had been shaved and scrubbed with antiseptic, and the orange-yellow sheen of betadine was apparent thanks to the bright overhead lights. The look on her face was curious, and not panicked in the least. The perfect patient.
“5…4…3…2…1… BEGIN!” The exact time was noted by another technician as the patient was sedated, intubated, and hooked up to an anesthesia machine—the surgical team had moved as if part of a well-choreographed dance, while the familiar beeping of the electrocardiogram machine began to echo eerily in the room like a metronome as it helped monitor her condition. Beep… beep… beep…
The surgeon’s skill was evident as within just minutes, a newborn baby puppy was tossed gently through the air, and I caught the little blob of flesh in the warm towel I held in my outstretched arms. I dashed with the precious cargo to a station that we had prepared in advance, and started cleaning mine up— followed closely by the other catchers with their own puppies in tow.
We removed each one from their amniotic sac, used a suction bulb to remove fluid from their mouths and noses to clear their upper respiratory tracts, and rubbed each one clean as the mother would, which stimulated them to breathe and cry. Although it’s no glamorous task, hearing that puppy cry is one of the most rewarding experiences in the world. Then, once the puppy was clean, dry, and stable, we each tied off our puppy’s umbilical cord with suture material, cut off the rest of the placenta, and placed the baby in a pre-warmed incubator until mom was recovered enough to take care of them.
- Radiograph image of canine fetuses in utero, courtesy of the Animal Hospital of Pasco (http://www.pascovets.com). Can you count how many puppies there are?
As you may have guessed, before I was a Science Writing student here at Hopkins, I had worked for a few years as a veterinary technician at an animal hospital back home. As a ‘vet tech,’ I was responsible for assisting the veterinarians in a similar manner to the way that nurses assist doctors in human hospitals. Since I always tell crazy animal stories to my classmates, we all thought my first post on this new blog should have something to do with animals, and perhaps one of the lesser-known procedures that are performed at an animal hospital. If you haven’t guessed by now, this is a canine or feline cesarean section.
Now many of you may scoff, thinking a c-section on animals? Well it’s actually more common than you might think. There are a number of reasons as to why it might have to be performed, such as the animal is way past her due date with no sign of parturition (birth), she is somehow too weak to give birth naturally, she is straining too much or having some kind of trouble (dystocia), the baby is stuck or improperly positioned near the birth canal (breeched), and so forth. In addition, some breeds almost always have to have cesarean sections performed because they have been bred to a point where their heads/hips are too oddly-shaped for natural birth to be possible. This is often the case with dogs that are extremely small, as well as pugs and other brachycephalic (flat-faced) dogs. It is almost impossible for bulldogs to be born naturally for this reason, and practically every pregnant female of this breed will have to have this procedure done.
I hope to never see a human doctor toss a newborn human baby to a nurse so she can catch it in a towel, but there actually is some science behind it when done with dogs and cats. After reading my first-person account, you may be slightly horrified and wonder why on earth a veterinarian would toss sweet little newborn puppies or kittens at his assistants rather than just handing them over. I spoke with Dr. Michael Petranto, a veterinarian with a special interest in animal reproduction and who is also the medical director at Twin Rivers Animal Hospital in East Windsor, New Jersey to shed some light on the subject.
He explained that the purpose of the toss/catch procedure, which is done during all veterinary c-sections, is mainly for speed. Plus, the entire surgery itself is carefully timed. “The ultimate goal,” he said, “is to resuscitate the pups or kittens as quickly as possible, get them warm and stable, and then get them nursing once mom is strong enough after surgery.” This is important because they must drink the mother’s “first milk” or colostrum, a substance rich in nutrients, proteins, and vital antibodies, which is only produced within 8 hours after birth.
The entire process can be done even faster when other technicians form an assembly-line, as opposed to the same person catching a baby, resuscitating it, and running back for another—that would take too long and some babies take longer than others to stabilize. This way the surgeon can just take each puppy or kitten and quickly toss one after another to a waiting technician who can give all their attention to the one they have.
If the mother is calm enough and behaves well, she will be prepped for surgery while she is awake. Usually for most other procedures, an animal’s surgical site is shaved and cleaned with antiseptic while they are under anesthesia in order to make it easier for the technicians, and to cause less stress for the animal. With c-sections, there is a concern for both the mother and her unborn litter, who can all be affected by the anesthetic drugs if they’re in the mother’s system for too long. The same holds true with people. Speed is the key.
The surgeon also has to remain sterile throughout the procedure. If the catchers get too close, they could run the risk of contaminating the doctor, as well as the surgical table and equipment if they were to accidentally touch anything. This could lead to the mother developing a dangerous infection. The doctor gently tosses the newborns one by one, which is only the distance of a few feet at most, in order to avoid this.
Dr. Petranto explained that in all his years of practice, he couldn’t remember a technician ever dropping a puppy or kitten during one of these procedures—they really have it down to an art. But, he said that even if one was dropped, natural birth would have been more traumatic. “Think about a Great Dane,” he said. “When a female is whelping [giving birth], those puppies are going to fall about the same distance if she happens to be standing. Plus the mothers pick them up, lick them, move them around and so forth. They get shaken up quite a bit and are pretty resilient.”
Interestingly, he also mentioned that many people ask if there is a different bond that forms between a mother and her litter after a cesarean section versus a natural birth, and the answer is that there may just be. As a matter of fact, there is a pheromone that the mother is stimulated to produce during natural birth that she does not during a c-section. Referred to as Appeasing Pheromone, it was only recently discovered within the last few years, and helps to calm the babies and reassure them. It also helps them become more confident and by so doing, encourages them to start exploring their surroundings as they get older. However, more research is needed at this point to determine if the lack of this pheromone in female animals who have had cesarean sections significantly affects their offspring in a negative way.
From what I have seen with my own eyes though, the mothers and their litters tend to turn out just fine.