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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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/

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Sea Urchins Pull Themselves Inside Out to be Reborn | Deep Look
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There’s Something Very Fishy About These Trees … | Deep Look
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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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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/

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

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KQED, an NPR and PBS affiliate based in San Francisco, serves the people of Northern California and beyond with a public-supported alternative to commercial media. Home to one of the most listened-to public radio station in the nation, one of the highest-rated public television services and an award-winning education program, KQED is also a leader and innovator in interactive media and technology, taking people of all ages on journeys of exploration — exposing them to new people, places and ideas.

Funding for Deep Look is provided in part by PBS Digital Studios and the John S. and James L. Knight Foundation. Deep Look is a project of KQED Science, which is supported by HopeLab, The David B. Gold Foundation; S. D. Bechtel, Jr. Foundation; The Dirk and Charlene Kabcenell Foundation; The Vadasz Family Foundation; Smart Family Foundation and the members of KQED.