Sea Star and Worm Swarm Explained

We assume that spineless sea critters like sea stars, worms, and urchins are loafers, idly existing while the real action happens around them. This time-lapse video from the BBC shows us just how wrong we are.

An unlikely army of harmless-looking creatures swarms over the corpse of a leopard seal, and what happens next isn't pretty. A bounty like this comes about once in a decade for these animals, and they'll feast for months.

The BBC does a pretty good job of explaining the basics of what's going on here. But let's learn a little more about the featured creatures' hunting habits. Sea stars, ribbon worms, sea urchins, and their cousins may be spineless, eyeless, and even toothless, but that doesn’t stop them from getting their meal on.

Ninja Stars

For all their beauty, sea stars (the preferred term for starfish, since they're echinoderms, not fish) are pretty ruthless hunters. Instead of eyes, a sea star has an eye spot at the end of each arm, which can sense light and dark. The sea star creeps over the ocean floor, groping for its next victim. Most of the time, these are of the crunchy outside/gooey inside variety: snails, barnacles, clams, and mussels. If a shellfish refuses to cooperate, the sea star will wrap its arms around the bivalve, then use its sticky tube feet to pry the shell open.

Once its prey is near, the sea star will eject its stomach, which oozes over the prey and digests it on the spot. After the prey has been liquefied, the sea star just sucks its stomach back in. Watch this sunflower star nonchalantly sidle up to a juicy-looking (and apparently slow-witted) wolf eel. Just, you know, being friendly.

Worm of Nightmares

Ribbon worms made headlines twice recently, first when a purple specimen spewed its branched proboscis on a man's hand, and again when a shamrock-green beast showed up in Taiwan. It may look silly on land, but in the water, the ribbon worm (phylum Nemertea) is not to be trifled with. They’re enormous, for one thing. The green species, Lineus fuscoviridis, can reach up to 6 feet long. But that’s nothing compared to the rest of its family. Scientists believe that Lineus longissimus may grow to nearly 200 feet. That’s longer than a blue whale, and a whole lot slimier.

Then there’s that proboscis. When a ribbon worm finds something worth eating, it lashes out like a chameleon with its extendable, sticky proboscis. And no morsel is too large; like pythons, ribbon worms can swallow creatures three to four times their own size. For even larger meals, like the seal in the video up top, some species make a hole (or find one), then slither in and eat their prey from the inside out.

Raccoons of the Sea

It’s no surprise that sea urchins turned up at the dead-seal party. They’re notorious trash-eaters, subsisting on algae, dead fish, and other sea garbage. Just as the urchin’s body is bristling with spines, its mouth, located on the underside of its body, bristles with big, sharp teeth. When they’re not gnawing on rotting flesh, urchins use their teeth to scrape algae off of rocks, which can apparently be pretty noisy.

Bonus! Other Unexpected Attackers

They might not have made an appearance in this video, but sea anemones are plenty gross in their own right. These relatives of urchins and sea stars look like beautiful, delicate flowers, but their tentacles are covered with neurotoxins, and they will eat anything they can grab. The giant green anemone pictured below is in the process of devouring an entire baby cormorant:

Image Credit: Lisa Habecker

Even clams, mussels, and oysters are not as defenseless as we long thought. Natural history accounts reaching back to the 19th century tell of birds felled by the very shellfish they intended to eat. After a 1996 storm on the Jersey Shore, huge numbers of surf clams washed up on the beach. Scientists combing the beach found almost 40 birds with their bills or feet snapped tight inside the shells of defiant clams. Some of these birds were able to shake their captors; others fell into the sea and drowned. So let’s not underestimate the little beasts! 

NOAA, Wikimedia Commons // Public Domain
Watch the First-Ever Footage of a Baby Dumbo Octopus
NOAA, Wikimedia Commons // Public Domain
NOAA, Wikimedia Commons // Public Domain

Dumbo octopuses are named for the elephant-ear-like fins they use to navigate the deep sea, but until recently, when and how they developed those floppy appendages were a mystery. Now, for the first time, researchers have caught a newborn Dumbo octopus on tape. As reported in the journal Current Biology, they discovered that the creatures are equipped with the fins from the moment they hatch.

Study co-author Tim Shank, a researcher at the Woods Hole Oceanographic Institution in Massachusetts, spotted the octopus in 2005. During a research expedition in the North Atlantic, one of the remotely operated vehicles he was working with collected several coral branches with something strange attached to them. It looked like a bunch of sandy-colored golf balls at first, but then he realized it was an egg sac.

He and his fellow researchers eventually classified the hatchling that emerged as a member of the genus Grimpoteuthis. In other words, it was a Dumbo octopus, though they couldn't determine the exact species. But you wouldn't need a biology degree to spot its resemblance to Disney's famous elephant, as you can see in the video below.

The octopus hatched with a set of functional fins that allowed it to swim around and hunt right away, and an MRI scan revealed fully-developed internal organs and a complex nervous system. As the researchers wrote in their study, Dumbo octopuses enter the world as "competent juveniles" ready to jump straight into adult life.

Grimpoteuthis spends its life in the deep ocean, which makes it difficult to study. Scientists hope the newly-reported findings will make it easier to identify Grimpoteuthis eggs and hatchlings for future research.

Joe Raedle, Getty Images
10 Things You Might Not Know About Grizzly Bears
Joe Raedle, Getty Images
Joe Raedle, Getty Images

Ursus arctos horribilis is better known by the more casual term of grizzly bear. These massive, brown-haired predators have a reputation as one of nature’s most formidable killing machines. Standing up to 8 feet tall and weighing 800 pounds, these fierce mammals have captivated—and frightened—humans for centuries. Keep your distance and read up on these facts about their love for munching moths, eating smaller bears, and being polar-curious.


Grizzlies—more accurately, North American brown bears—are strong enough to make a meal out of whatever they like, including moose, elk, and bison. Despite their reputation for having carnivorous appetites, their diet also consists of nuts, berries, fruits, and leaves. They’ll even eat mice. The gluttony doesn’t kick in until they begin to exhibit hyperphagia, preparing for winter hibernation by chomping down enough food to gain up to three pounds a day.


A grizzly bear eats fruit in Madrid, Spain
Dani Pozo, AFP/Getty Images

More than 700 grizzlies live in or near Yellowstone National Park, which forces officials to constantly monitor how park visitors and the bears can peacefully co-exist. Because bears rummaging in food containers can lead to unwanted encounters, the park’s Grizzly & Wolf Discovery Center tests trash cans and coolers to see if they’re bear-resistant. (Nothing is truly bear-proof.) Often, a bear will use “CPR,” or jumping on a canister with its front legs, in order to make the lid pop off. Containers that can last at least 60 minutes before being opened can be advertised by their manufacturers as being appropriate for bear-inhabited environments.


It's a myth that grizzlies can't climb trees. Though their weight and long claws make climbing difficult [PDF], and they need support from evenly-spaced branches, grizzlies can travel vertically if they choose to.


Two grizzly bears play in a pool at a zoo in France
Jean-Francois Monier, AFP/Getty Images

In addition to being omnivorous, grizzlies can also be classified as cannibals. They’ve been spotted eating the carcasses of black bears in Canada. Calling it a “bear-eat-bear world,” officials at Banff National Park in Alberta said the grizzlies are “opportunistic” and more than willing to devour black bears—sometimes just one-fifth their size—if the occasion calls for it. And it’s not just black bears: One study on bear eating habits published in 2017 recorded a 10-year-old male eating a 6-year-old female brown bear.


Although grizzlies enjoy eating many insects, moths are at the top of the menu. Researchers have observed that bears are willing to climb to alpine heights at Montana’s Glacier National Park in order to feast on the flying appetizers. Grizzlies will turn over rocks and spend up to 14 hours in a day devouring in excess of 40,000 moths.


A grizzly bear appears at the Wild Animal Sanctuary in Keenseburg, Colorado
John Moore, Getty Images

In what would be considered an ill-advised decision, explorer Zebulon Pike decided to gift his friend President Thomas Jefferson with two grizzly cubs in 1807. Jefferson reluctantly accepted them and kept them in a cage near the north entrance to the White House, and later re-gifted the cubs to museum operator Charles Willson Peale. Sadly, one of them got shot after getting too aggressive with Peale’s family.


The bears we see in fiction or lazing about in the wild tend to look cumbersome and slow, as most anything weighing nearly a half-ton would. But in a land race, even Olympic champions would be on the losing end. Grizzlies can reportedly run 35 mph, and sustain speeds of up to 28 mph for two miles, faster than Usain Bolt’s 27.78 miles per hour stride (which he can only sustain for a few seconds).


A grizzly bear is shown swimming at a pool in an Illinois zoo
Scott Olson, Getty Images

In parts of Alaska and Canada where grizzlies and polar bears converge, there are sometimes rare sightings of what observers call “grolar bears” or “pizzlies.” With large heads and light-colored fur, they’re a hybrid superbear birthed from some interspecies mating. Typically, it’s male grizzlies who roam into those territories, finding female polar bears to cozy up with. Researchers believe climate change is one reason the two are getting together.


When it comes to intellect, grizzlies may not get all the same publicity that birds and whales do, but they’re still pretty clever. The bears can remember hotspots for food even if it’s been 10 years since they last visited the area; some have been observed covering tracks or obscuring themselves with rocks and trees to avoid detection by hunters.


A grizzly bear and her cub walk in Yellowstone National Park
Karen Bleier, AFP/Getty Images

For 42 years, grizzlies at Yellowstone occupied the endangered species list. That ended in 2017, when the U.S. Fish and Wildlife Service declared that a rise in numbers—from 150 in the 1970s to more than 700 today—meant that conservation efforts had been successful. But overall, the grizzly population is still struggling: Fewer than 2000 remain in the lower 48 states, down from 50,000 two centuries ago.


More from mental floss studios