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Caterpillar's Sugary Cocktail Transforms Ants Into Aggressive Bodyguards

Scientists have long observed the relationship between Japanese oakblue butterfly (Narathura japonica) caterpillars and some nearby ants (Pristomyrmex punctatus). The caterpillars secrete a sugary substance for the ants to feed on, and in turn the ants protect the caterpillar as it grows inside oak tree leaves.

But recently, Masaru Hojo from Kobe University in Japan noticed that each caterpillar was always guarded by the same ants, which “never moved away or returned to their nests,” he told New Scientist. Was there something in the sweet secretions that was rendering the ants unable or unwilling to care about anything beyond attending to the caterpillar—even finding food to sustain themselves? 

To test this theory, Hojo and his colleagues conducted lab experiments in which they allowed some ants to interact with the caterpillars and feed on the secretions, and kept others separate as a control. The control ants that didn't drink the sugar droplets remained free to come and go as they pleased. But those that fed on the secretions stayed with the caterpillar, abandoning their nests. What's more, whenever the caterpillar turned its tentacles inside out, the ants suddenly started acting violently. Meanwhile, the ants who had not consumed the secretion remained unaffected by the caterpillar's behavior. Something in the secretions seemed to be drugging the ants, turning them into zombies that were controlled by the caterpillar.

Hojo speculates that this control over the ants is used in the wild as a form of protection. Rather than fight its own battles, the caterpillar responds to predators by inducing the ants to behave aggressively. “There are glandular cells near the tentacles that could be secreting chemical signals,” Hojo said. “It is possible that both visual and chemical signals are stimulating the ant aggression.”

The researchers, who published the results of their experiment in a recent issue of Current Biologyaren't sure what it is about the secretion that gives the caterpillar mind control over the ants, but it appears to be related to dopamine. The doped-up ants had lower levels of dopamine and, when treated with a drug called reserpine—which blocks the transport of dopamine—even the ants that had consumed the secretion stopped responding to the caterpillars' tentacles.

Hojo and other scientists unrelated to the study say these findings call into question many interspecies relationships thought to be mutualistic—but some people aren't so quick to dismiss the existing beliefs.

“The benefit for the caterpillar is obvious, but we do not know whether the benefit for the ants is as minimal as the authors argue,” Martin Heil, of the Center for Research and Advanced Studies of the National Polytechnic Institute in Irapuato, Mexico, told New Scientist. "If the liquid that the caterpillars secrete is sufficiently nutritious, then it might well be that the overall balance for the ants also is positive."

[h/t New Scientist]

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The Surprising Reason Why Pen Caps Have Tiny Holes at the Top
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If you’re an avid pen chewer, or even just a diehard fan of writing by hand, you’re probably well acquainted with the small hole that tops off most ballpoint pen caps, particularly those classic Bic Cristal pens. The reason it’s there has nothing to do with pen function, it turns out. As Science Alert recently reported, it’s actually designed to counter human carelessness.

Though it’s arguably unwise—not to mention unhygienic—to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps. Companies like Bic know this well—so they make pen caps that won’t impede breathing if they’re accidentally swallowed.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard [PDF].

Pen cap inhalation is a real danger, albeit a rare one, especially for primary school kids. A 2012 study [PDF] reported that pen caps account for somewhere between 3 and 8 percent of “foreign body aspiration,” the official term for inhaling something you’re not supposed to. Another study found that of 1280 kids (ages 6 to 14) treated between 1997 and 2007 for foreign body inhalation in Beijing, 34 had inhaled pen caps.

But the standards help keep kids alive. In that Beijing study, none of the 34 kids died, and the caps were successfully removed by doctors. That wasn’t always the case. In the UK, nine children asphyxiated due to swallowing pen caps between 1970 and 1984. After the UK adopted the international standard for air holes in pen caps, the number of deaths dropped precipitously [PDF]. Unfortunately, it’s not foolproof; in 2007, a 13-year-old in the UK died after accidentally swallowing his pen cap.

Even if you can still breathe through that little air hole, getting a smooth plastic pen cap out of your throat is no easy task for doctors. The graspers they normally use to take foreign bodies out of airways don’t always work, as that 2012 case report found, and hospitals sometimes have to employ different tools to get the stubbornly slippery caps out (in that study, they used a catheter that could work through the hole in the cap, then inflated a small balloon at the end of the catheter to pull the cap out). The procedure doesn’t exactly sound pleasant. So maybe resist the urge to put your pen cap in your mouth.

[h/t Science Alert]

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Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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