Why Do Tumbleweeds Tumble? | Deep Look

The silent star of classic Westerns is a plant on a mission. It starts out green and full of life. It even grows flowers. But to reproduce effectively, it needs to turn into a rolling brown skeleton.

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DEEP LOOK is a ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.

Tumbleweeds might be the iconic props of classic Westerns. But in real life, they’re not only a noxious weed, but one that moves around. Pushed by gusts of wind, they can overwhelm entire neighborhoods, as happened recently in Victorville, California, or become a threat for drivers and an expensive nuisance for farmers.

“They tumble across highways and can cause accidents,” said Mike Pitcairn, who tracks tumbleweeds at the California Department of Food and Agriculture in Sacramento. “They pile up against fences and homes.”

And tumbleweeds aren’t even originally from the West.

Genetic tests have shown that California’s most common tumbleweed, known as Russian thistle, likely came from Ukraine, said retired plant population biologist Debra Ayres, who studied tumbleweeds at the University of California, Davis.

A U.S. Department of Agriculture employee, L. H. Dewey, wrote in 1893 that Russian thistle had arrived in the U.S. through South Dakota in flaxseed imported from Europe in the 1870s.

“It has been known in Russia many years,” Dewey wrote, “and has quite as bad a reputation in the wheat regions there as it has in the Dakotas.” This is where the name Russian thistle originates, said Ayres, although tumbleweeds aren’t really thistles.

The weed spread quickly through the United States — on rail cars, through contamination of agricultural seeds and by tumbling.
“They tumble to disperse the seeds,” said Ayres, “and thereby reduce competition.”

By bouncing and rolling, a tumbleweed spreads out tens of thousands of seeds so that they all get plenty of sunlight and space.

Tumbleweeds grow well in barren places like abandoned agricultural fields, vacant lots or the side of the road, where they can tumble unobstructed and there’s no grass, which their seedlings can’t compete with.

— Where does a tumbleweed come from?

Tumbleweeds start out as any plant, attached to the soil. Seedlings, which look like blades of grass with a bright pink stem, sprout at the end of the winter. By summer, Russian thistle plants take on their round shape and grow flowers. Inside each flower, a fruit with a single seed develops.

Other plants attract animals with tasty fruits, and get them to carry away their seeds and disperse them when they poop.

Tumbleweeds developed a different evolutionary strategy. Starting in late fall, they dry out and die, their seeds nestled between prickly leaves. Gusts of wind easily break dead tumbleweeds from their roots and they roll away, spreading their seeds as they go.

— How big do tumbleweeds grow?

Mike Pitcairn, of the California Department of Food and Agriculture, said they can grow to be more than 6 feet tall in parts of the state like the San Joaquin Valley.

— Are tumbleweeds dangerous?

Yes. They can cause traffic accidents, and they can be a fire hazard if they pile up against buildings.

—+ More great Deep Look episodes:

How Ticks Dig In With a Mouth Full of Hooks
https://www.youtube.com/watch?v=_IoOJu2_FKE

This Giant Plant Looks Like Raw Meat and Smells Like Dead Rat
https://www.youtube.com/watch?v=ycUNj_Hv4_Y

Upside-Down Catfish Doesn’t Care What You Think
https://www.youtube.com/watch?v=eurCBOJMrsE

—+ See some great videos and documentaries from the PBS Digital Studios!

Above the Noise: Why Is Vaping So Popular?
https://www.youtube.com/watch?v=P9zps5LsVXs

Hot Mess: What Happened to Nuclear Power?
https://www.youtube.com/watch?v=_jEXZZDU6Gk

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—+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the Templeton Religion Trust and the Templeton World Charity Foundation, the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

Upside-Down Catfish Doesn’t Care What You Think

You might suppose this catfish is sick, or just confused. But swimming belly-up actually helps it camouflage and breathe better than its right-side-up cousins.

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DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe and meet extraordinary new friends. Explore big scientific mysteries by going incredibly small.

Normally, an upside-down fish in your tank is bad news. As in, it’s time for a new goldfish.

That’s because most fish have an internal air sac called a “swim bladder” that allows them to control their buoyancy and orientation. They fill the bladder with air when they want to rise, and deflate it when they want to sink. Fish without swim bladders, like sharks, have to swim constantly to keep from dropping to the bottom.

If an aquarium fish is listing to one side or flops over on its back, it often means it has swim bladder disease, a potentially life-threatening condition usually brought on parasites, overfeeding, or high nitrate levels in the water.

But for a few remarkable fish, being upside-down means everything is great.

In fact, seven species of catfish native to Central Africa live most of their lives upended. These topsy-turvy swimmers are anatomically identical to their right-side up cousins, despite having such an unusual orientation.

People’s fascination with the odd alignment of these fish goes back centuries. Studies of these quizzical fish have found a number of reasons why swimming upside down makes a lot of sense.

In an upside-down position, fish produce a lot less wave drag. That means upside-down catfish do a better job feeding on insect larvae at the waterline than their right-side up counterparts, who have to return to deeper water to rest.

There’s something else at the surface that’s even more important to a fish’s survival than food: oxygen. The gas essential to life readily dissolves from the air into the water, where it becomes concentrated in a thin layer at the waterline — right where the upside-down catfish’s mouth and gills are perfectly positioned to get it.

Scientists estimate that upside-down catfishes have been working out their survival strategy for as long at 35 million years. Besides their breathing and feeding behavior, the blotched upside-down catfish from the Congo Basin has also evolved a dark patch on its underside to make it harder to see against dark water.

That coloration is remarkable because it’s the opposite of most sea creatures, which tend to be darker on top and lighter on the bottom, a common adaptation called “countershading” that offsets the effects of sunlight.

The blotched upside-down catfish’s “reverse” countershading has earned it the scientific name negriventris, which means black-bellied.

— How many kinds of fish swim upside down?

A total of seven species in Africa swim that way. Upside-down swimming may have evolved independent in a few of the species – and at least one more time in a catfish from Asia.

— How do fish stay upright?

They have an air-filled swim bladder on the inside that that they can fill or deflate to maintain balance or to move up or down in the water column.

— What are the benefits of swimming upside down?

Upside down, a fish swims more efficiently at the waterline, where there’s more oxygen and better access to some prey.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/2018/04/14/the-mystery-of-the-upside-down-catfish

—+ For more information:

The California Academy of Sciences has upside-down catfish in its aquarium collection: https://www.calacademy.org/exhibits/steinhart-aquarium

—+ More Great Deep Look episodes:

Take Two Leeches and Call Me in the Morning
https://youtu.be/O-0SFWPLaII

This Is Why Water Striders Make Terrible Lifeguards
https://youtu.be/E2unnSK7WTE

—+ See some great videos and documentaries from the PBS Digital Studios!

PBS Eons: What a Dinosaur Looks Like Under a Microscope
https://www.youtube.com/watch?v=4rvgiDXc12k

Origin of Everything: The Origin of Race in the USA
https://www.youtube.com/watch?v=CVxAlmAPHec

—+ Follow KQED Science:

KQED Science: http://www.kqed.org/science
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—+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

Take Two Leeches and Call Me in the Morning | Deep Look

(FYI – This episode is a *bit* more bloody that usual – especially a little after the 2-minute mark. Just letting you know in case flesh wounds aren’t your thing)

The same blood-sucking leeches feared by hikers and swimmers are making a comeback… in hospitals. Once used for questionable treatments, leeches now help doctors complete complex surgeries to reattach severed body parts.

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DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.

Leeches get a bad rap—but they might not deserve it. Yes, they’re creepy crawly blood-suckers. And they can instill an almost primal sense of disgust and revulsion. Humphrey Bogart’s character in the 1951 film The African Queen even went so far as to call them “filthy little devils.”

But the humble leech is making a comeback. Contrary to the typical, derogatory definition of a human “leech,” this critter is increasingly playing a key role as a sidekick for scientists and doctors, simply by being its bloodthirsty self.

Distant cousins of the earthworm, most leech species are parasites that feed on the blood of animals and humans alike. They are often found in freshwater and navigate either by swimming or by inching themselves along, using two suckers—one at each end of their body—to anchor themselves.

Upon reaching an unsuspecting host, a leech will surreptitiously attach itself and begin to feed. It uses a triangular set of three teeth to cut in, and secretes a suite of chemicals to thin the blood and numb the skin so its presence goes undetected.

—+ Read the entire article on KQED Science: https://www.kqed.org/science/1921659/take-two-leeches-and-call-me-in-the-morning

—+ For more information:
David Weisblat at UC Berkeley studies leeches development and evolution
https://mcb.berkeley.edu/labs/weisblat/research.html

Biologists recently reported that leeches in that region can provide a valuable snapshot of which animals are present in a particular area
https://www.tandfonline.com/doi/abs/10.1080/14772000.2018.1433729?journalCode=tsab20&

—+ More Great Deep Look episodes:

Why the Male Black Widow is a Real Home Wrecker | Deep Look
https://www.youtube.com/watch?v=NpJNeGqExrc

For Pacific Mole Crabs It’s Dig or Die | Deep Look
https://www.youtube.com/watch?v=tfoYD8pAsMw

Praying Mantis Love is Waaay Weirder Than You Think | Deep Look
https://www.youtube.com/watch?v=NHf47gI8w04&t=83s

—+ See some great videos and documentaries from the PBS Digital Studios! Above the Noise:

Cow Burps Are Warming the Planet | Reactions
https://www.youtube.com/watch?v=MnRFUSGz_ZM

What a Dinosaur Looks Like Under a Microscope | Eons
https://www.youtube.com/watch?v=4rvgiDXc12k
Hawking Radiation | Space Time
https://www.youtube.com/watch?v=qPKj0YnKANw

—+ Follow KQED Science:
KQED Science: http://www.kqed.org/science
Tumblr: http://kqedscience.tumblr.com
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—+ About KQED KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

How Ticks Dig In With a Mouth Full of Hooks | Deep Look

Why can’t you just flick a tick? Because it attaches to you with a mouth covered in hooks, while it fattens up on your blood. For days. But don’t worry – there *is* a way to pull it out.

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DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.

Spring is here. Unfortunately for hikers and picnickers out enjoying the warmer weather, the new season is prime time for ticks, which can transmit bacteria that cause Lyme disease.

How they latch on – and stay on – is a feat of engineering that scientists have been piecing together. Once you know how a tick’s mouth works, you understand why it’s impossible to simply flick a tick.

The key to their success is a menacing mouth covered in hooks that they use to get under the surface of our skin and attach themselves for several days while they fatten up on our blood.

“Ticks have a lovely, evolved mouth part for doing exactly what they need to do, which is extended feeding,” said Kerry Padgett, supervising public health biologist at the California Department of Public Health in Richmond. “They’re not like a mosquito that can just put their mouth parts in and out nicely, like a hypodermic needle.”

Instead, a tick digs in using two sets of hooks. Each set looks like a hand with three hooked fingers. The hooks dig in and wriggle into the skin. Then these “hands” bend in unison to perform approximately half-a-dozen breaststrokes that pull skin out of the way so the tick can push in a long stubby part called the hypostome.

“It’s almost like swimming into the skin,” said Dania Richter, a biologist at the Technische Universität in Braunschweig, Germany, who has studied the mechanism closely. “By bending the hooks it’s engaging the skin. It’s pulling the skin when it retracts.”

The bottom of their long hypostome is also covered in rows of hooks that give it the look of a chainsaw. Those hooks act like mini-harpoons, anchoring the tick to us for the long haul.

“They’re teeth that are backwards facing, similar to one of those gates you would drive over but you’re not allowed to back up or else you’d puncture your tires,” said Padgett.

— How to remove a tick.
Kerry Padgett, at the California Department of Public Health, recommends grabbing the tick close to the skin using a pair of fine tweezers and simply pulling straight up.

“No twisting or jerking,” she said. “Use a smooth motion pulling up.”

Padgett warned against using other strategies.

“Don’t use Vaseline or try to burn the tick or use a cotton swab soaked in soft soap or any of these other techniques that might take a little longer or might not work at all,” she said. “You really want to remove the tick as soon as possible.”

— What happens if the mouth of a tick breaks off in your skin?
Don’t worry if the tick’s mouth parts stay behind when you pull.

“The mouth parts are not going to transmit disease to people,” said Padgett.

If the mouth stayed behind in your skin, it will eventually work its way out, sort of like a splinter does, she said. Clean the bite area with soap and water and apply antibiotic ointment.

—+ Read the entire article on KQED Science: https://www.kqed.org/science/1920972/how-ticks-dig-in-with-a-mouth-full-of-hooks

—+ For more information:
Centers for Disease Control information on Lyme disease:
https://www.cdc.gov/lyme/

Mosquito & Vector Control District for San Mateo County, California:
https://www.smcmvcd.org/ticks

—+ More Great Deep Look episodes:

How Mosquitoes Use Six Needles to Suck Your Blood
https://www.youtube.com/watch?v=rD8SmacBUcU

So … Sometimes Fireflies Eat Other Fireflies
https://www.youtube.com/watch?v=oWdCMFvgFbo

Meet the Dust Mites, Tiny Roommates That Feast On Your Skin
https://www.youtube.com/watch?v=ACrLMtPyRM0

—+ See some great videos and documentaries from the PBS Digital Studios!

Above the Noise: Are Energy Drinks Really that Bad?
https://www.youtube.com/watch?v=5l0cjsZS-eM

It’s Okay To Be Smart: Inside an ICE CAVE! – Nature’s Most Beautiful Blue
https://www.youtube.com/watch?v=P7LKm9jtm8I

—+ Follow KQED Science:
KQED Science: http://www.kqed.org/science
Tumblr: http://kqedscience.tumblr.com
Twitter: https://www.twitter.com/kqedscience

—+ About KQED
KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

So … Sometimes Fireflies Eat Other Fireflies | Deep Look

Most firefly flashes are pure romance, a sexy form of skywriting. But one variety copies the mating signals of others to lure them to their demise.

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DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe and meet extraordinary new friends. Explore big scientific mysteries by going incredibly small.

Most of the blinking signals that fireflies send out are intended to attract mates. But researchers are finding out that in some cases, these romantic overtures are not all wine and roses.

Females of one firefly group, the genus Photuris, have learned to copy other fireflies’ flashes to attract the males of those species. When one arrives, she pounces, first sucking his blood, then devouring his insides.

These “femme fatale” fireflies live throughout the Eastern U.S alongside the fireflies they target. They can develop widely varying light shows to target whatever species are in the area.

The predatory habits of Photuris are just one example of how much individual firefly signals can differ from one another.

The male Common Eastern Firefly, for example, is known for his fish hook-shaped aerial maneuver, which he repeats at six-second intervals. That characteristic move has earned the species the nickname “Big Dipper.”

The male Big Dipper hopes this bit of skywriting will get him noticed by females hiding in the grass. If the female likes what she sees, her reply comes as a single pulse from her smaller, heart-shaped lantern. That’s his invitation to land and mate.

Most firefly interactions follow the same pattern, with roving males advertising themselves to concealed females. Within a species, the back-and-forth signals are so reliable that it’s easy to attract the male fireflies with even a simple decoy.

Firefly light is biochemical. But fireflies like the Big Dippers do much more with chemistry than just make light. They can mix together an array of other compounds, including invisible pheromones for mating, and others called lucibufagins (“loosa-BOOF-ajins”) that ward off predators like spiders and birds.

At some point, the Photuris “femme fatale” fireflies lost the ability to make their own lucibufagins. So instead of chemistry, these bigger, stronger fireflies became adept at imitation, and evolved to turn into insect vampires to take these valuable compounds from other fireflies to boost their own defenses.

And it works. In experiments, predators avoided Photuris fireflies that had recently preyed on other fireflies.

— Where do fireflies live?

There are fireflies worldwide, but in the U.S., you’ll find them in the Midwest and Eastern U.S. There are a few species in the West, including the California Pink Glow-worm.

— Why do fireflies flash?

Mostly, it’s to attract mates. One sex, usually the male, uses a more elaborate flash pattern to get the attention of the opposite sex. Then the female signals her interest with a simpler flash.

— Why do fireflies glow after they die?

The chemicals in the firefly that make light, luciferin and luciferase, remain viable after it dies, and the reaction that creates the light thrives on oxygen, which is of course plentiful in the air.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/2018/02/27/so-sometimes-fireflies-eat-other-fireflies

—+ For more information:

Join Fireflyers International: https://fireflyersinternational.net/

—+ More Great Deep Look episodes:

Everything You Never Wanted to Know About Snail Sex
https://youtu.be/UOcLaI44TXA

Why the Male Black Widow is a Real Home Wrecker
https://youtu.be/NpJNeGqExrc

—+ See some great videos and documentaries from the PBS Digital Studios!

PBS Eons: When Giant Fungi Ruled
https://www.youtube.com/watch?v=-G64DagHuOg

Origin Of Everything: Why Do We Eat Artificial Flavors?
https://www.youtube.com/watch?v=iNaJ31EV13U

—+ Follow KQED Science:

KQED Science: http://www.kqed.org/science
Tumblr: http://kqedscience.tumblr.com
Twitter: https://www.twitter.com/kqedscience

—+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

For Pacific Mole Crabs It’s Dig or Die | Deep Look

Pacific mole crabs, also known as sand crabs, make their living just under the surface of the sand, where they’re safe from breaking waves and hungry birds. Some very special physics help them dig with astonishing speed.

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DEEP LOOK is a ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe. Explore big scientific mysteries by going incredibly small.

* NEW VIDEOS EVERY OTHER TUESDAY! *

Among the surfers and beach-casting anglers, there’s a new visitor to San Francisco’s Ocean Beach shoreline.

Benjamin McInroe is there for only one reason — to find Pacific mole crabs, a creature commonly known as “sand crabs” — and the tiny animals whose burrowing causes millions of small bubbles to appear on the beach as the tide comes in and out.

McInroe is a graduate student from UC Berkeley studying biophysics. He wants to know what makes these little creatures so proficient at digging their way through the wet sand.

McInroe hopes that he can one day copy their techniques to build a new generation of digging robots.

— What are Pacific Mole Crabs?

Pacific mole crabs, also known as sand crabs, are crustaceans, related to shrimp and lobsters. They have four pairs of legs and one pair of specialized legs in the front called uropods that look like paddles for digging in sand. Pacific mole crabs burrow through wet sand and stick their antennae out to catch bits of kelp and other debris kicked up by the breaking waves.

— What makes those holes in the sand at the beach?

When the waves recede, mole crabs burrow down into the sand to keep from being exposed. They dig tail-first very quickly leaving holes in the wet sand. The holes bubble as water seeps into the holes and the air escapes.

— What do birds eat in the wet beach sand?

Shore birds like seagulls rush down the beach as the waves recede to catch mole crabs that haven’t burrowed down quickly enough to escape. The birds typically run or fly away as the next wave breaks and rolls in.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/science/2018/02/13/for-pacific-mole-crabs-its-dig-or-die/

—+ For more information:

Benjamin McInroe, a Ph.D. student at UC Berkeley, studies how Pacific mole crabs burrow
https://www.ocf.berkeley.edu/~bmcinroe/

Professor Robert Full directs the Poly-PEDAL Lab at UC Berkeley, where researchers study the physics of how animals and use that knowledge to build mechanical systems like robots based on their findings.
http://polypedal.berkeley.edu/

—+ More Great Deep Look episodes:

Decorator Crabs Make High Fashion at Low Tide | Deep Look
https://youtu.be/OwQcv7TyX04

These Fish Are All About Sex on the Beach | Deep Look
https://youtu.be/j5F3z1iP0Ic

Sea Urchins Pull Themselves Inside Out to be Reborn | Deep Look
https://youtu.be/ak2xqH5h0YY

There’s Something Very Fishy About These Trees … | Deep Look
https://www.youtube.com/watch?v=rZWiWh5acbE&t=1s

—+ See some great videos and documentaries from the PBS Digital Studios!

Why Do We Eat Artificial Flavors? | Origin of Everything
https://www.youtube.com/watch?v=iNaJ31EV13U

The Facts About Dinosaurs & Feathers
https://www.youtube.com/watch?v=aOeFRg_1_Yg

Why Is Blue So Rare In Nature?
https://www.youtube.com/watch?v=3g246c6Bv58

—+ Follow KQED Science

KQED Science: http://www.kqed.org/science
Tumblr: http://kqedscience.tumblr.com
Twitter: https://www.twitter.com/kqedscience

—+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

Why the Male Black Widow is a Real Home Wrecker | Deep Look

Sure, the female black widow has a terrible reputation. But who’s the real victim here? Her male counterpart is a total jerk — and might just be getting what he deserves.

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DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe and meet extraordinary new friends. Explore big scientific mysteries by going incredibly small.

We’ve all heard the stories. She mates and then kills. Her venom is 15 times stronger than a rattlesnake’s. One bite could kill you. With a shiny black color and a glaring red hourglass stomach, she has long inspired fear and awe.

But most species of widow spider (there are 31), including the western black widow found in the U.S., don’t kill their mates at all. Only two widow spider species always eat their mate, the Australian redback and the brown widow, an invasive species in California.

And the male seems to be asking for it. In both of these species, he offers himself to her, somersaulting into her mouth after copulation.

He may even deserve it. During peak mating season, thousands of males will prowl around looking for females. Females set up their webs, stay put and wait.

Once the male arrives at her silken abode, he starts to wreck it, systematically disassembling her web one strand at a time. In a process scientists call web reduction, he bunches it into a little ball and wraps it up with his own silk.

Then, while mating, he will wrap her in fine strands that researchers refer to as the bridal veil. He drapes his silk over her legs, where her smell receptors are most concentrated.

After all of that, he is most likely to crawl away, alive and unscathed.

— Why does the black widow spider eat her mate?

No one really knows, but scientists assume his body supplies her with nutrition for laying eggs. Sometimes she eats him by accident, not recognizing him as a mate.

— How harmful are black widows to people?

We couldn’t find a documented case of a human death from a black widow spider in the U.S., but a bite will make you sick with extreme flu-like symptoms. Luckily, black widows aren’t aggressive to people.

— Why do black widows have a red hourglass?

It’s a warning sign, a phenomenon common in nature that scientists call aposematicism, which is the use of color to ward off enemies.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/science/2018/01/09/why-the-male-black-widow-is-a-real-home-wrecker

—+ For more information:

Black widow researcher Catherine Scott’s website: http://spiderbytes.org/

—+ More Great Deep Look episodes:

Why Is The Very Hungry Caterpillar So Dang Hungry?
https://www.youtube.com/watch?v=el_lPd2oFV4

Everything You Never Wanted to Know About Snail Sex
https://www.youtube.com/watch?v=UOcLaI44TXA

—+ See some great videos and documentaries from the PBS Digital Studios!

Origin of Everything: Why Does Santa Wear Red?
https://www.youtube.com/watch?v=fajNM5OPVnA

PBS Eons: ‘Living Fossils’ Aren’t Really a Thing
https://www.youtube.com/watch?v=mPvZj2KcjAY

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