13 Facts About Nurse Sharks


Known as the “couch potato of the shark world,” the nurse shark (Ginglymostoma cirratum) leads a sedentary life. By day, it rests, and by night, it creeps over the sandy floors and coral reefs of its shallow-water habitat, slurping up little animals along the way.

But though it's not a fast or aggressive fish, you should give it plenty of space: People who act carelessly around nurse sharks risk serious injuries. Here are 13 things that every ocean-lover ought to know about the nurse shark.


For certain sharks, lying on the ocean floor is an impossibility. Species like the great white and the whale shark breathe by swimming nonstop; as they travel around, water is constantly flowing into their open mouths and across their gills, supplying oxygen en route. If the fish stop moving for too long, that flow ceases and they die. But other species are perfectly capable of breathing while sitting still—including the nurse shark. By using oral muscles to actively suck water into the mouth—what's called buccal pumping—it can supply oxygen to the gills without needing to swim anywhere.


Wild nurse sharks are usually found in shallow, coastal waters. The fish are nocturnal predators who tend to hunt within 65 feet of the ocean’s surface (although adults sometimes rest in deeper waters during the daylight hours). They spend their lives around coral reefs and coastal shelves, and most of their hunting takes place right on the ocean floor, where these slow-moving carnivores look for prey in or near the sand. Instead of swimming, they sometimes use their pectoral fins to “walk” across the bottom.


Barbels are fleshy sense organs that contain taste buds, which they drag across sand in search of prey.


Nurse sharks eat a variety of sea life, from conchs, squid, and sea urchins to bony fish. A cavity within the throat generates a powerful suction which vacuums hapless animals up into the nurse shark’s mouth, where rows of tiny, backward-curving teeth crush up the food.

The mouth works like a dental conveyor belt; new rows of teeth pop up towards the back and gradually push older ones forward until they fall out. How long an individual row lasts depends on the season. During the winter, a nurse shark will acquire a fresh row of teeth every 50 to 70 days. But in the summer, tooth row replacement occurs every 10 to 20 days.


Full-grown nurse sharks are usually brown, but they can also be grey or yellowish. In 1992, a “milk white” individual with brown splotches was caught and photographed near Key Largo, Florida. The fish might have been piebald, which is a genetic condition that’s similar to albinism. Piebald animals have a combination of normally colored skin and patches of pigment-deficient white skin. Another mature nurse shark who fit this general description was filmed in 2014. Adult specimens don't normally have spots, but as juveniles, the fish are covered in little black dots that fade as they age.


Shark snuggle parties are a thing. By day, the nocturnal nurse shark becomes inactive; for hours on end, it just lies around and pumps water over its gills. Crevices, ledges, and piles of boulders are popular downtime locations for this species. Although the sharks don't socialize on hunting trips, they often recline en masse. Nurse sharks are known to rest communally, with groups of two to 40 individuals piling up on top of each other.


The maximum reliably-measured length for this species is 10.1 feet. As far as weight goes, the heaviest adult ever reported to the International Game and Fish Association was a 263.8-pounder caught by two fishermen (a father and his 15-year-old son) in 2007. Day-old pups are 7.8 to 12 inches long—and a batch of premature nurse sharks who were measured by scientists after being born near-term weighed between 4.2 and 5.3 ounces apiece. Big things can start out small.


It’s definitely not qualified to care for hospital patients, so why did people start calling this barbel-faced sea critter the “nurse” shark? That’s a linguistic mystery, but historians have their theories. Maybe the suction-based feeding methods reminded sailors of nursing infants. Alternatively, the nurse in nurse shark could be descended from “huss,” an archaic name given to an unrelated family of bottom-dwellers. (We now call them “catsharks.”) Over time, huss evolved into nuss, a word that came to mean “shark” or “large fish.” So perhaps the nurse shark moniker is based on a corruption of nuss.


Approaching 40 feet in total length and weighing several tons, adult whale sharks are the biggest fish presently alive. Like the nurse shark, this species eats via suction, and that’s not where the resemblance stops. Whale and nurse sharks are both members of the order Orectolobiformes, a group of 39 shark species largely in temperate and tropical oceans. Also known as “carpet sharks,” they're characterized by having small mouths that—when viewed in profile—do not extend behind the eyes. All of these fish have two dorsal fins on their backs and five sets of gill slits. Species within this order tend to have striking patterns on their skins, with grown-up nurse sharks being an obvious exception. Barbels are another common feature.

The strangest member of Orectolobiformes might be the shaggy wobbegong sharks, who lie still on tropical sea beds and use brilliant camouflage to ambush unsuspecting fish from below.


Plenty of well-known sharks embark on huge migrations; hundreds of whale sharks from across the Atlantic visit Mexico’s Yucatan Peninsula every summer and Pacific great whites go on winter pilgrimages to a mysterious, mid-ocean site dubbed the “White Shark Café.” Nurse sharks are less prone to wanderlust; many remain in the same general area all year round.

But some of their peers might feel the travel bug from time to time. In January 2018, Environmental Biology of Fishes published a 23-year nurse shark tracking study. The scientists behind it looked at a wild population which uses the Dry Tortugas (part of the Florida Keys) as a mating ground. Altogether, they captured and recaptured 76 adult nurse sharks. Tagging revealed that some of these fish clung to the Dry Tortugas and neighboring islands throughout the year. However, others were venturing as far north as the Tampa Bay area in between mating seasons, making the shark “partially migratory.” That means some individuals within this species migrate, but others don't.


The nurse shark mating season lasts from May to July, during which females will mate with multiple males. Sometimes two, three, or more males will attempt to mate with the same female simultaneously, resulting in violent shoving matches.

Nurse sharks have a five- or six-month gestation period and give birth to litters of 20 to 40 live young. A single batch of newborn pups may include the offspring of up to six different fathers. After she’s given birth, a mother nurse shark won’t mate again for another 18 months.


Underestimate this animal at your own risk. Because nurse sharks are sluggish by nature, commonly kept in aquariums, and don't possess large teeth, a lot of people who swim or dive in their natural habitat assume that the fish aren’t dangerous. But these predators can crush clams between their teeth and generate enough suction to rip a full-grown conch right out of its shell—so you don’t want one latching onto your arm.

But that’s just what happened to a swimmer in Boca Raton, Florida, in 2016. The 23-year-old female victim had been out snorkeling with friends when a 2-foot-long nurse shark clamped down on her right arm. (Eyewitnesses reported that another group of beachgoers had been harassing it.) The shark remained there while the snorkeler was driven to a nearby hospital. She survived, but the shark died before the medical team showed up. In another 2018 incident, an Instagram model was bitten while posing in some nurse shark-inhabited shallows.

Nurse shark attacks are uncommon, but they’re certainly not unheard-of—and humans are usually to blame. YouTube is loaded with videos of scuba divers hugging, grabbing, or stroking wild nurse sharks. Docile and shy as nurse sharks are, they may bite when provoked—or if they mistake an arm or finger for food.

“People are playing with fire,” George Burgess, the longtime director of the International Shark Attack File database, told the Palm Beach Post. In an interview with Newsweek, Burgess said that “A nurse shark bite is one of the worst, because their teeth are like cheese graters on each side. When they get onto a human being, it’s like a vacuum cleaner … They leave a concave hole where they’ve turned flesh into hamburger.”


Ginglymostoma cirratum lives in the Caribbean, off the northeastern coast of South America, near Spain, along western Africa, and by the eastern U.S. seaboard. A 2012 study found that a population living in the tropical eastern Pacific was genetically and anatomically different enough from Atlantic nurse sharks to constitute its own species. Named Ginglymostoma unami, or the Pacific nurse shark, it has a couple of noticeable traits that set it apart from G. cirratum. For example, the newly named fish’s second dorsal fin lies closer to the tail [PDF]. The two species may have diverged from one another when tectonic plates collided about 3 million years ago, isolating the ancestral nurse shark populations on either side of the Panamanian land bridge.

Chimpanzees Bond by Watching Movies Together, Too

Windzepher/iStock via Getty Images
Windzepher/iStock via Getty Images

Scientists at the Wolfgang Kohler Primate Research Center in Germany recently discovered that, like humans, chimpanzees bond when they watch movies together, the BBC reports.

In the study, published in Proceedings of the Royal Society B, researchers stationed pairs of chimpanzees in front of screens that showed a video of a family of chimps playing with a young chimp. They found that afterward, the chimps would spend more time grooming and interacting with each other—or simply being in the same part of the room—than they would without having watched the video.

They gave the chimps fruit juice to keep them calm and occupied while they viewed the video, and they chose a subject that chimps have previously proven to be most interested in: other chimps. They also used eye trackers to ensure the chimps were actually watching the video. If you’ve ever watched a movie with friends, you might notice similarities between the chimps’ experience and your own. Drinks (and snacks) also keep us calm and occupied while we watch, and we like to watch movies about other humans. Since this study only showed that chimps bond over programs about their own species, we don’t know if it would work the same way if they watched something completely unrelated to them, like humans do—say, The Lion King.

Bonding through shared experiences was thought to be one of the traits that make us uniquely human, and some researchers have argued that other species don’t have the psychological mechanisms to realize that they’re even sharing an experience with another. This study suggests that social activities for apes don’t just serve utilitarian purposes like traveling together for safety, and that they’re capable of a more human-like social closeness.

The part that is uniquely human about this study is the fact that they were studying the effect of a screen, as opposed to something less man-made. The chimps in question have participated in other studies, so they may be more accustomed to that technology than wild apes. But the study demonstrates that we’re not the only species capable of social interaction for the sake of social interaction.

[h/t BBC]

10 Facts You Should Know About Mosquitoes

tskstock/iStock via Getty Images
tskstock/iStock via Getty Images

Between the itching and the welts and the fears of mosquito-borne viruses, it's easy to forget that mosquitoes are a wonder of evolution, and that maybe they don't get a fair shake from us. Of more than 3000 known species, only 80 actually bite people, and at least one eats other mosquitoes for us. They grow from egg to adult in just five days, begin mating within minutes of hatching, and possess, by way of their stinging mouthparts, some of the coolest appendages in the animal kingdom.

1. Mosquitoes are excellent flyers in bad weather.

The average raindrop is 50 times heavier than the average mosquito, yet they buzz around in the rain with no problems. If a Boeing 747 got whacked with a similarly scaled-up raindrop, there would be 2375 tons of water coming down on it, and things probably wouldn’t turn out as well as they do for the mosquito. How do the insects do it?

A common urban legend said that the bugs were nimble enough to dodge the drops. A few years ago, a team of engineers from the Georgia Institute of Technology watched real mosquitoes and Styrofoam dummy mosquitoes with a high-speed camera during a rainy flight to see if that’s what was really happening. They found that the bugs don’t fly fast enough to dodge the drops, but their slowness is what keeps them from getting knocked out of the sky. A mosquito’s low mass even at slow speed doesn’t provide enough of a target for a raindrop to splash on collision. Instead, the drop just deforms, and doesn’t transfer enough momentum to the mosquito to disrupt its flight.

2. Texas is the mosquito capital of America.

Of the 3000 species of mosquitoes around the world, at least 150 are found in the United States, and 85 of those call Texas home. When people say everything's bigger in Texas, you can also include the biodiversity of the state's biting, disease-carrying insects.

3. Some mosquitoes are truly dangerous to humans ...

The female mosquito, which is the one that stings and sucks blood, is an incredible transmitter of disease and, because of that, the deadliest animal in the world. Each year, the malaria parasites they transmit kill 2 million to 3 million people and infect another 200 million or more. They also spread pathogens that cause yellow fever, dengue fever, Rift Valley fever, Chikungunya and West Nile disease.

4. ... and some mosquitoes are harmless.

Not every species of mosquito sucks blood from people, and among those that do, not every one transmits disease. The blood suckers don’t even need to bite you for every meal. Males live entirely on nectar and other plant fluids, and the females’ diet is primarily plant-based, too. Most of the time, they only go after people when they’re ready to reproduce, because blood contains lipids, proteins, and other nutrients needed for the production of eggs.

5. MosquitoEs actually help the environment.

When you’re rubbing calamine lotion all over yourself, mosquitoes might not seem to serve any purpose but to annoy you, but many species play important ecological roles. The mosquitoes Aedes impiger and Aedes nigripes, which gather in thick clouds in Arctic Russia and Canada, are an important food source for migrating birds. Farther south, birds, insects, spiders, salamanders, lizards, frogs, and fish also eat different mosquito species regularly. Plants need them, too, and some, like the blunt-leaved orchid and endangered monkeyface orchid, rely on mosquitoes as their primary pollinator.

Some mosquito species are also excellent at mosquito control. Species of the genus Toxorhynchites feed on the larvae and immature stages of other mosquitoes and will sometimes even cannibalize members of their own species.

6. Mosquitoes are amazing hunters (as if we needed to tell you that).

Mosquitoes are adept at picking up on the chemicals given off by their human hosts. They can detect the carbon dioxide in our breath, the 1-octen-3-ol in our breath and sweat, and other organic substances we produce with the 70-plus types of odor and chemical receptors in their antennae. These receptors can pick up traces of chemicals from hundreds of feet away, and once the mosquito closes in, it tracks its meal chemically and also visually—and they’re fond of people wearing dark colors.

7. Mosquitoes can be picky.

If it seems like you’re always covered head to toe by bites while people who were sitting right next to you only have one or two, it’s not just paranoia; the skeeters actually are out to get you. Some people happen to give off more of the odors and compounds that mosquitoes find simply irresistible, while others emit less of those and more of the compounds that make them unattractive to mosquitoes—either by acting as repellents or by masking the compounds that mosquitoes would find attractive.

8. A female mosquito's mouth is primed for sucking blood.

A mosquito doesn’t simply sink its proboscis into your skin and start sucking. What you see sticking out of a mosquito’s face is the labium, which sheaths the mouthparts that really do all the work. The labium bends back when a mosquito bites, allowing these other parts to pass through its tip and do their thing. The sharp, pointed mandibles and maxillae, which both come in pairs, are used to pierce the skin, and the hollow hypopharynx and the labrum are used to deliver saliva and draw blood, respectively.

9. Mosquito saliva prevents blood clotting.

The saliva that gets pumped out from the hypopharynx during a bite is necessary to get around our blood’s tendency to clot. It contains a grab bag of chemicals that suppress vascular constriction, blood clotting and platelet aggregation, keeping our blood from clogging up the mosquitoes' labrum and ruining their meal.

10. Mosquitoes can explode.

Blood pressure makes a mosquito's meal easier by helping to fill its stomach faster, but urban legend says it can also lead to their doom. Story goes, you can flex a muscle close to the bite site or stretch your skin taut so the mosquito can’t pull out its proboscis and your blood pressure will fill the bug until it bursts. The consensus among entomologists seems to be that this is bunk, but there is a more complicated way of blowing the bugs up. To make a blood bomb, you’ve got to sever the mosquito’s ventral nerve cord, which transmits information about satiety. When it's cut, the cord can’t tell the mosquito’s brain that its stomach is full, so it’ll keep feeding until it reaches critical mass. At least one researcher found that mosquitoes clueless about how full they were would keep sucking even after their guts had exploded, sending showers of blood spilling out of their blown-out back end.