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.

11 Things You Might Not Know About Reindeer

Mats Lindberg/iStock via Getty Images
Mats Lindberg/iStock via Getty Images

Beyond their sled-pulling capabilities and discrimination against those with red noses, what do you really know about reindeer?

1. Reindeer and caribou are the same thing.

Historically, the Eurasian reindeer and American caribou were considered to be different species, but they are actually one and the same: Rangifer tarandus. There are two major groups of reindeer, the tundra and the woodland, which are divided according to the type of habitat the animal lives in, not their global location. The animals are further divided into nine to 13 subspecies, depending on who is doing the classification. One subspecies, the Arctic reindeer of eastern Greenland, is extinct.

2. Reindeer have several names.

Reindeer comes from the Old Norse word hreinin, which means "horned animal.” Caribou comes from Canadian French and is based on the Mi'kmaq word caliboo, meaning “pawer” or "scratcher," in reference to the animal’s habit of digging through the snow for food.

3. Santa’s reindeer are most likely R. tarandus platyrhynchus, a subspecies from Svalbard.

Svalbard reindeer
pum_eva/iStock via Getty Images

Clement C. Moore’s poem, "A Visit from Saint Nicholas,” introduced the world to Santa’s reindeer and describes them as "tiny." The only reindeer that could really be considered tiny are the Svalbard subspecies, which weighs about half as much as most reindeer subspecies and are at least a foot shorter in length. That may prove useful when landing on roofs.

Strangely, you’ll almost never see these guys in depictions of Santa. Live-action films usually use full-sized reindeer and animations usually draw the creatures as a cross between a white-tailed deer and a reindeer.

4. It’s not always easy to tell the sex of a reindeer.

In most deer species, only the male grows antlers, but that’s not true for most reindeer. Although the females in certain populations do not have antlers, many do. During certain times of year, you can still tell the sex of a reindeer by checking for antlers. That’s because males lose their antlers in winter or spring, but females shed theirs in the summer.

5. Santa’s reindeer may or may not be female.

Since reindeer shed their antlers at different points of the year based on their sex and age, we know that Santa’s reindeer probably aren't older males, because older male reindeer lose their antlers in December and Christmas reindeer are always depicted with their antlers. Female Svalbard deer begin growing their antlers in summer and keep them all year. That means Santa’s sled either has to be pulled by young reindeer, constantly replaced as they start to age, or Santa’s reindeer are female.

6. Reindeer were originally connected to Santa through poetry.

Before Moore wrote “A Visit from Saint Nicholas” (a.k.a. “The Night Before Christmas”) in 1823, no one thought about reindeer in conjunction with Santa Claus. Moore introduced the world to Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Dunder and Blixem (the last two of which were later changed from Dutch to German, becoming Donner and Blitzen). While the first six names all make sense in English, the last two in German mean “thunder” and “flash,” respectively.

As for little Rudolph, he wasn’t introduced until catalog writer Robert L. May wrote a children’s book in verse for his employer, Montgomery Ward, in 1939 titled “Rudolph the Red-Nosed Reindeer.”

7. Reindeer are the only mammals that can see ultraviolet light.

Humans can see light in a range of wavelengths, from about 700 nanometers (in the red spectrum) to 400 nanometers (in the violet spectrum). Reindeer can see light to 320 nanometers, in the ultraviolet (UV) range. This ability lets reindeer see things in the icy white of the Arctic that they would otherwise miss—kind of like viewing the glow of a white object under a blacklight. Things like white fur and urine are difficult, even impossible, for humans to see in the snow, but for reindeer, they show up in high contrast.

8. Reindeer evolved for life in cold, harsh environments.

Migrating caribou
Geoffrey Reynaud/iStock via Getty Images

Life in the tundra is hard, but reindeer have it easy-ish thanks to their amazing evolutionary enhancements. Their noses are specially adapted to warm the air they breathe before it enters their lungs and to condense water in the air, which keeps their mucous membranes moist. Their fur traps air, which not only helps provide them with excellent insulation, but also keeps them buoyant in water, which is important for traveling across massive rivers and lakes during migration.

Even their hooves are special. In the summer, when the ground is wet, their foot pads are softened, providing them with extra grip. In the winter, though, the pads tighten, revealing the rim of their hooves, which is used to provide traction in the slippery snow and ice.

9. some reindeer migrate longer distances than any other land mammal.

A few populations of North American reindeer travel up to 3100 miles per year, covering around 23 miles per day. At their top speed, these reindeer can run 50 miles per hour and swim at 6.2 miles per hour. During spring, herd size can range from 50,000 to 500,000 individuals, but during the winter the groups are much smaller, when reindeer enter mating season and competition between the bucks begins to split up the crowds. Like many herd animals, the calves learn to walk fast—within only 90 minutes of being born, a baby reindeer can already run.

10. Reindeer play an important role in Indigenous cultures.

In Scandinavia and Canada, reindeer hunting helped keep Indigenous peoples alive, from the Mesolithic and Neolithic periods all the way through modern times. In Norway, it is still common to find reindeer trapping pits, guiding fences, and bow rests dating from the Stone Age. And in Scandinavia, reindeer is still a popular meat, sold in grocery stores in fresh, canned, and dried forms. Almost all of the animal’s organs are edible and many are crucial ingredients of traditional dishes in the area. In North America, Inuit rely on caribou for traditional food, clothing, shelter, and tools.

11. Reindeer used to live farther south.

Reindeer now live exclusively in the northern points of the globe, but when Earth was cooler and humans were less of a threat, their territory was larger. In fact, reindeer used to range as far south as Nevada, Tennessee, and Spain during the Pleistocene area. Its habitat has shrunk considerably in the last few centuries. The last caribou in the contiguous United States was removed to a Canadian conservation breeding program in 2019.

As for how Santa's nine reindeer manage to fly while pulling a sled carrying presents for every child in the whole world, science still hasn’t worked that out.

Why Thousands of 'Penis Fish' Washed Up on a California Beach

Kate Montana, iNaturalist // CC BY-NC 4.0
Kate Montana, iNaturalist // CC BY-NC 4.0

Nature works in mysterious ways. The latest example materialized at Drakes Beach near San Francisco, California, in early December, when visitors strolling along the shore stumbled upon what looked to be the discarded inventory of an adult novelty shop. In fact, it was thousands of Urechis caupo, a marine worm that bears more than a passing resemblance to a human penis.

The engorged pink invertebrate, which is typically 10 inches in length, is native to the Pacific coast and frequently goes by the less salacious name of “fat innkeeper worm.” Burrowing in sand, the worm produces mucus from its front end to ensnare plankton and other snacks, then pumps water to create a vacuum where the food is directed into their tunnel. Since it builds up a small nest of discarded food, other creatures like crabs will stop by to feed, hence the “innkeeper” label.

You can see the worm in "action" here:

Because the worms enjoy a reclusive life in their burrows, it’s unusual to see thousands stranded on the beach. It’s likely that a strong storm broke up the intertidal sand, decimating their homes and leaving them exposed. The event is likely to thrill otters, as they enjoy dining on the worm. So do humans: Penis fish are served both raw and cooked in Korea and China.

[h/t Live Science]