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Why Don't Spiders Get Stuck in Their Webs?

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When a bug flies into a spider web, the game is over. It’s almost instantly stuck, and a sitting duck for the web’s owner. When you or I walk into a web, we’re a little better off than the bug because we won’t be dinner, but the sticky strands of web are still a pain in the butt to pick off of clothes and skin.

The spider itself, which spends much more time in contact with the web than you or any bug, doesn’t seem to have any issues getting stuck as it moves around. What gives?

For a long time, people thought spiders didn’t get stuck because their legs were coated in an oil made inside their bodies. With their legs lubed up like this, there was nothing for the silk web strands to stick to. Early 20th century naturalists proposed this idea — that the spider “varnishes herself with a special sweat,” as one elegantly put it — after observing spiders in the wild. The hitch is that, for all the research on spiders scientists have done in the meantime, no one had bothered to test the idea until recently.

A study published last year by two biologists in Costa Rica, Daniel Briceño and William Eberhard, suggests that spiders stay unstuck thanks to a combination of behavior, anatomy and, yes, even an oily non-stick coating.

What a Web They Weave

The first thing that helps spiders from getting trapped is that not every part of every web is sticky. In many orb weaver spider webs, for example, only the spiral threads are made with sticky silk. The “spokes” that support the structure of the web and the center part of the web where the spider rests are made with “dry” silk.

Using the center area and the spokes, a spider can move all around the web, and even off of it, without any concern for getting stuck.

Neat Feet

The spiders that Briceño and Eberhard studied used the dry threads for moving around most of the time, but when prey landed on the webs and the spiders went to retrieve their dinner, they inevitably had to charge across a sticky section. Unlike their prey, though, the spiders didn’t just whack into the sticky threads willy-nilly. The scientists found that the spiders walk very carefully when on the sticky sections, holding their body clear of the web and making minimal contact with the threads with only the tips of their legs.

Under a microscope, Briceño and Eberhard saw that the sticky threads do indeed make contact with the spider and stick to the setae, or short bristly hairs, on their legs. As a spider pulls its leg of the web, though, the droplets of adhesives that sit on the thread slide toward the edge of the bristle, where they have contact with only the thin tip and easily pull away. All these bristles are also in irregular rows and break free from the sticky droplets one by one, not all at once, which keeps the adhesive force of multiple droplets from combining.

Smooth Like That

What is it about the setae that lets them shed the web’s adhesives so easily? When Briceño and Eberhard washed a detached spider leg and applied it to a sticky thread, the leg stuck and wasn’t as easily removed. They figured that the bristles must have either a chemical coating of anti-adhesive substances or a structural surface layer with anti-adhesive properties. After analyzing several compounds washed off the the spiders’ legs, they found several several oily substances — including n-dodecane, n-tridecane, and n-tetradecane — that could act as a non-stick coating.

The researchers couldn’t tell where the chemicals had come from, but scientists’ descriptions from the last century suggested that they were applied by the spider’s mouth. Sure enough, when Briceño and Eberhard washed a live spider’s legs, it passed each of the legs through its mouthparts, but they didn’t test whether or not any anti-adhesive material was being applied.

To see if the spiders were coating their own legs would require a pretty simple experiment, Eberhard told me via email, but the spider they were working with, Nephila clavipes, is only seasonally abundant. The study would have to wait until the population climbed again, so the source of the non-stick chemicals is still a mystery for now. In the meantime, he said, he’s looking into how spiders deal with a different type of silk, called cribellum silk, which can be sticky without being wet.

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Big Questions
Do Bacteria Have Bacteria?
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Drew Smith:

Do bacteria have bacteria? Yes.

We know that bacteria range in size from 0.2 micrometers to nearly one millimeter. That’s more than a thousand-fold difference, easily enough to accommodate a small bacterium inside a larger one.

Nothing forbids bacteria from invading other bacteria, and in biology, that which is not forbidden is inevitable.

We have at least one example: Like many mealybugs, Planococcus citri has a bacterial endosymbiont, in this case the β-proteobacterium Tremblaya princeps. And this endosymbiont in turn has the γ-proteobacterium Moranella endobia living inside it. See for yourself:

Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)
Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)

I don’t know of examples of free-living bacteria hosting other bacteria within them, but that reflects either my ignorance or the likelihood that we haven’t looked hard enough for them. I’m sure they are out there.

Most (not all) scientists studying the origin of eukaryotic cells believe that they are descended from Archaea.

All scientists accept that the mitochondria which live inside eukaryotic cells are descendants of invasive alpha-proteobacteria. What’s not clear is whether archeal cells became eukaryotic in nature—that is, acquired internal membranes and transport systems—before or after acquiring mitochondria. The two scenarios can be sketched out like this:


The two hypotheses on the origin of eukaryotes:

(A) Archaezoan hypothesis.

(B) Symbiotic hypothesis.

The shapes within the eukaryotic cell denote the nucleus, the endomembrane system, and the cytoskeleton. The irregular gray shape denotes a putative wall-less archaeon that could have been the host of the alpha-proteobacterial endosymbiont, whereas the oblong red shape denotes a typical archaeon with a cell wall. A: archaea; B: bacteria; E: eukaryote; LUCA: last universal common ancestor of cellular life forms; LECA: last eukaryotic common ancestor; E-arch: putative archaezoan (primitive amitochondrial eukaryote); E-mit: primitive mitochondrial eukaryote; alpha:alpha-proteobacterium, ancestor of the mitochondrion.

The Archaezoan hypothesis has been given a bit of a boost by the discovery of Lokiarcheota. This complex Archaean has genes for phagocytosis, intracellular membrane formation and intracellular transport and signaling—hallmark activities of eukaryotic cells. The Lokiarcheotan genes are clearly related to eukaryotic genes, indicating a common origin.

Bacteria-within-bacteria is not only not a crazy idea, it probably accounts for the origin of Eucarya, and thus our own species.

We don’t know how common this arrangement is—we mostly study bacteria these days by sequencing their DNA. This is great for detecting uncultivatable species (which are 99 percent of them), but doesn’t tell us whether they are free-living or are some kind of symbiont. For that, someone would have to spend a lot of time prepping environmental samples for close examination by microscopic methods, a tedious project indeed. But one well worth doing, as it may shed more light on the history of life—which is often a history of conflict turned to cooperation. That’s a story which never gets old or stale.

This post originally appeared on Quora. Click here to view.

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Big Questions
Why Do Cats 'Blep'?
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As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
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If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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