Christian Grill, Wikimedia Commons // CC BY-SA 3.0
Christian Grill, Wikimedia Commons // CC BY-SA 3.0

In a First for Fish, Needlefish Attack Prey from the Air

Christian Grill, Wikimedia Commons // CC BY-SA 3.0
Christian Grill, Wikimedia Commons // CC BY-SA 3.0

Off the east coast of Australia, fish are doing something funny. On two separate occasions, biologist Ryan Day has seen needlefish employ a novel hunting tactic, launching themselves out of the water and attacking their prey from the air. 

As far as he knows, Day says, “this is the first report of a fish leaping from the water to facilitate predation on other fishes.”

Needlefish, also known as Long Toms, live up to their name. They’re long and slender, and have long jaws lined with plenty of sharp teeth. They live and feed close to the water’s surface and are known for leaping out of the water to make quick escapes from their predators. They can launch out of the water at around 40 miles per hour and even skitter across the surface on their tails. Day says the fishes’ “proclivity for going airborne has resulted in severe injury and even death to people struck by needlefishes” while boating or swimming.

While watching needlefish hunt small baitfish around Australia’s Heron Island, Day saw the fish put these leaps to another use. After stalking their prey and moving in on them slowly, some of the needlefish proceeded with what’s considered their typical approach, swimming through the school of baitfish and then lunging through the water at a targeted fish.

Other needlefish, though, took a different tack. As Day and his colleagues report in the Journal of Fish Biology, as the needlefish neared their prey, they made a “leaping attack,” jumping out of the water and plunging back in right in the middle of the baitfish school, where they nabbed a fish in their jaws. These leaping attacks weren’t flukes: They accounted for half of the attacks the researchers observed.

The researchers saw the same thing while doing field work in another spot near North Stradbroke Island. Here, the needlefish made their leaps from the breaking fronts of waves, the team writes, “appearing to use the energy of the waves to propel them forward.”

The biologists think there are a few reasons needlefish might take to the air to make their attacks. First, the method extends the range they’re able to strike from. Needlefish typically lunge at their targets from around 1.5 feet away. At Heron Island, the fish started their leaping attacks when they were six feet away from the targets, increasing their attack range fourfold. This lets them strike sooner and from farther away, giving their prey less time to see them and escape. 

Aerial attacks also rob the prey of an escape path. When needlefish attack while in the water, the scientists saw, their prey often flee like the needlefish themselves do, leaping out of the water and skittering across the surface. Attacks from above cut the baitfish off from this route, though, and force them to scatter and swim deeper.

It’s also possible that the needlefish are jumping out of the water to hide from their targets. Because of the way light bends as it moves from air to water, a fish’s view of the sky when it looks up at the surface is condensed into a tight circle, creating an "optical manhole" effect known as Snell’s Window. Outside the window, things appear dark or mirror the ocean’s depths or floor. An object in the sky directly above the fish would be pretty clearly visible and appear at full size, the researchers explain, but an object at the boundary of Snell’s Window would appear smaller, dimmer and even blurry or broken up. To a fish, these objects would look farther away than they really are, or might be hard to see at all. The researchers think that the needlefish may be taking advantage of this effect, and jumping into the air to disappear from their prey’s sight right before an attack.

Needlefish aren’t the only fish to use Snell’s Window—or the open sky—to their advantage. Their cousins the flying fish are well known for leaping out of the water and launching themselves at shallow angles to hide from predators on the edges of the optical manhole. And while needlefish are the first to use aerial attacks on prey in the water, other fish sometimes leap out of the water to grab prey in the air. Just last year, scientists in South Africa documented tigerfish leaving the water to attack birds mid-flight.

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13 Facts About Opossums
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Opossums, which include the roughly 100 species in the order Didelphimorphia, are some of the most misunderstood animals in the Americas. They’re often thought of as dimwitted, dirty creatures whose most impressive trick is acting like roadkill. The truth is just the opposite: Opossums are smarter, cleaner, and more beneficial to humans than many of their woodland neighbors. Read on for more opossum facts.

1. OPOSSUMS AND POSSUMS AREN’T THE SAME ANIMAL.

In North America, opossum and possum describe the same thing, but in Australia the word possum refers to a completely different animal. Among the most well known of their respective types are the Virginia opossum and the brushtail possum. Both are small to medium sized, omnivorous marsupials, but the similarities end there. The possum looks like a cute cross between a squirrel and a chinchilla and it belongs to a different order than the North American mammal that shares (most of) its name. Despite the potential for confusion, possum is accepted as the shortened version of opossum in this part of the world (and if you see the word possum in this list, you can assume it’s referring to the animal from the Americas).

2. THEY’RE THE ONLY MARSUPIALS FOUND NORTH OF MEXICO.

Marsupials—mammals that carry and nurse their young in pouches—are absent from much of the world, and in Canada and the United States opossums are the sole representatives of the group. Like other marsupials, mother possums give birth to tiny, underdeveloped offspring (called joeys) that immediately crawl into a pouch where they live and nurse during their first months of life. Only once they’ve grown big and strong enough do they venture out, transitioning between their mother’s back and the warmth of the pouch until they mature into adults.

3. THEY CAN’T CHOOSE WHEN THEY PLAY DEAD.

Possum playing dead.
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Perhaps the most famous characteristic of the opossum is its tendency to play dead in front of predators. When the animal experiences intense fear in the face of danger, it seizes up and flops to the ground where it can remain for hours staring blankly ahead and sticking out its tongue. It’s an impressive defensive mechanism, but its effectiveness can’t be chalked up to the possum’s acting skills. Possums have no control over when they play dead or for how long they do it: The comatose-like state is an involuntary reaction triggered by stress.

4. AN OFFENSIVE ODOR SELLS THE PERFORMANCE.

A picture of a possum playing dead doesn’t really do it justice. To get the full experience, you need to be standing over to it to smell the putrid odor it emits when pretending to be a corpse. The smelly substance it secretes from its anus is just one more reason for foxes and bobcats to look for their dinner elsewhere.

5. THEY SLOW THE SPREAD OF LYME DISEASE.

Even if possums aren’t the cutest creatures in the forest, they should be a welcome addition to your backyard. Unlike other mammals that carry ticks, and therefore spread Lyme Disease, possums gobble up 90 percent of the ticks that attach to them. According to the National Wildlife Federation, a single possum consumes 5000 of the parasites per tick season. That means the more possums that are in your area, the fewer ticks you’ll encounter.

6. THEIR MEMORIES ARE SURPRISINGLY SHARP.

Possum looking up at table.
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Opossums have impressive memories—at least when it comes to food. Researchers found that possums are better at remembering which runway led to a tasty treat than rats, cats, dogs, and pigs. They can also recall the smell of toxic substances up to a year after trying them.

7. THEY’RE IMMUNE TO MOST SNAKE VENOM.

While most animals look at a snake and see danger, a possum sees its next meal. The animals are immune to the venom of nearly every type of snake found in their native range, the one exception being the coral snake. Possums take advantage of this adaptation by chowing down on snakes on a regular basis.

Researchers have been trying to harvest possums’ antivenom powers for decades. A few years ago, a team of scientists made progress on this front when they recreated a peptide found in possums and and found that mice given the peptide and rattlesnake venom were successfully protected from the venom’s harmful effects.

8. THEY ALMOST NEVER GET RABIES.

While possums aren’t totally immune to rabies (a few cases have been documented), finding a specimen with the disease is extremely unlikely. Marsupials like possums have a lower body temperature than the placental mammals that dominate North America—in other words, their bodies don’t provide a suitable environment for the virus.

9. THEIR TAIL ACTS AS A FIFTH APPENDAGE.

Baby opossum hanging from a tree branch by its tail.
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Opossums are one of a handful of animals with prehensile tails. These appendages are sometimes used as an extra arm: They can carry grass and leaves for building nests or grip the sides of trees to provide extra stability while climbing. Baby possums can even use their tails to hang from branches upside down as they’re often depicted doing in cartoons. But it’s a myth that possums sleep this way: Their tails are only strong enough to hold them for a short amount of time.

10. THEY’RE CONSTANTLY SELF-GROOMING.

Thanks to their whole acting-and-smelling-like-a-corpse routine, opossums aren’t known as the most sanitary animals in nature. But they take cleanliness seriously: The Washington Department of Fish and Wildlife writes that possums, like housecats, use their tongue and paws to groom themselves frequently and thoroughly. Possums largely lack sweat glands, and this behavior is believed to help them cool down. It also has the added effect of rendering them odorless (when they’re not secreting stinky predator-repellant, that is).

11. THEIR EYES AREN’T TOTALLY BLACK.

Close-up on opossum's face.
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One of the opossum’s most recognizable features is its pair of opaque eyes. Opossum eyes do have whites and irises, but because their pupils are so large, their eyes appear completely black from a distance. The exaggerated pupil dilation is thought to help the nocturnal animals see after the sun goes down.

12. THEY’RE SOCIAL CREATURES.

It was long assumed that opossums like to keep to themselves, but a study published in the journal Biology Letters suggests they have a social side. Researchers at the Federal University of Pernambuco in Recife, Brazil observed some possums in captivity sharing dens even if they weren’t mates. In one case, 13 white-eared opossums of various age groups were cohabiting the same space. The scientists suspect that male and female possums living in the wild may even build nests together as a way to trigger the female’s reproductive hormones.

13. THEIR REPRODUCTIVE SYSTEMS ARE COMPLICATED.

The way it gives birth and raises its young isn’t the only thing that’s interesting about the opossum's reproductive life. Females have two vaginal tracts and two uteri, and males in turn have a forked or bifurcated penis. This is fairly typical for marsupials, but when European colonizers first landed in North America centuries ago, they didn’t know what to make of the confusing genitalia. One explanation they came up with was that male opossums impregnated females through the nose.

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Hero Crayfish Cheats Death By Removing Its Own Claw to Escape Pot of Boiling Water
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There remains a perpetual debate over the ethical consequences of taking a crustacean and boiling it alive. In early 2018, Switzerland actually made it illegal to give living lobsters a scalding hot bath. (Instead, chefs are expected to stun them electronically before submersion.) Scientists can’t reach a conclusion over whether decapods feel pain—or if we can even define what that means for them.

While humans argue, some clawed sacrifices are taking action. A crayfish filmed by a Facebook user in China is making the internet rounds and being hailed as a hero after taking dramatic measures to escape a boiling pot of water.

In the footage, the crayfish appears to be unable to extricate its left appendage from a bubbling vat of doom. Rather than succumb, the crayfish uses its right claw to sever its compromised claw and scurry off. At 11 seconds, it’s the best summary of a Saw film possible.

“Juike,” the user who originally posted the video to the Weibo social media site, says he has taken the crafty invertebrate home and put him in an aquarium as a pet. The tiny survivalist may even regrow his lost limb, as crawfish are able to do, although it might not reach its former size.

Crayfish are in inherent danger of being turned into soup in China, where specialty restaurants devoted to their preparation are popping up. Some observers believe their popularity is due to diners having to step away from phones and social media in order to use both hands to peel away at their shells.

[h/t BBC]

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