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Why Won’t These Bugs Cross This Line?

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One of the most tightly-controlled borders in the world is a strip of forest in northwest Tasmania. It runs almost 125 miles and separates two areas by as little as 330 feet in some places. Those that live on one side of the border rarely, if ever, cross to the other. The border isn’t a geographical barrier or a wall, and it doesn’t separate political entities or ethnic groups. Rather, it’s an invisible line where two related species of millipedes meet, but don’t mix—and no one knows why. 

On the western side of the border lives Tasmaniosoma compitale, a 15 millimeter long, yellow-brown millipede. On the eastern side is T. hickmanorum, a similarly sized red-brown millipede in the same genus. Both species were named and scientifically described in 2010 by Bob Mesibov, a millipede specialist and research associate at the Queen Victoria Museum and Art Gallery in Launceston, Tasmania. He describes them and related species as a “head + 19 rings” (the head + 17 segments with limbs + 1 segment without legs + the telson, or end segment). Mesibov spent two years mapping the species’ ranges as preparation for further field studies. When all was said and done, he had an image of a very clear division that he could not explain.

Biogeographers, the scientists that study the spatial distribution of species, have a name for these cases where species meet, but overlap very little or not at all: parapatry. It’s very common with millipedes, and occurs with other invertebrates, some plants, and some vertebrates, like birds. Normally, parapatric boundaries follow some other natural boundary like a river or the edge of a climate zone. This millipede border, though, is the longest and narrowest of any that Mesibov has seen in Australian millipedes, and doesn’t have any apparent environmental or ecological cause. It rises from sea level at Tasmania’s north coast to some 700 meters in elevation and then drops back down to sea level. It crosses many of the island’s western coastal rivers and the headstreams of two major inland river systems in the area. It runs over different geological barriers and covers different soil and vegetation types and local climates. The border seemingly ignores the vast differences in topography, geology, climate, and vegetation that it covers, and maintains its sharpness for its whole length. 


Strong as the border is, Mesibov did find places where each species had managed to cross over into the other’s territory. There’s an “island” of T. hickmanorum surrounded by T. compitale range that’s at least 15 square miles and maybe bigger—Mesibov hasn’t found its outer edge yet. There’s also a group of T. hickmanorum living several miles into T. compitale territory, where they might have been accidentally dropped by a cattle truck.

For now, Mesibov can only speculate that the border is the result of some biological arrangement between the two species, and its origin and the way it’s maintained are a mystery. It’s one that he’ll leave to other biologists to solve as he continues his regular research finding, naming, and describing millipedes new to science (he’s got 100+ under his belt, so far). 

Whoever takes up the border question will have their work cut out for them. Further mapping and investigation is hindered by the fact that parts of the border cross through pastures, farms and other private property, as well as unroaded and inaccessible wilderness. 

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Big Questions
Why Don't We Eat Turkey Tails?
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Turkey sandwiches. Turkey soup. Roasted turkey. This year, Americans will consume roughly 245 million birds, with 46 million being prepared and presented on Thanksgiving. What we don’t eat will be repurposed into leftovers.

But there’s one part of the turkey that virtually no family will have on their table: the tail.

Despite our country’s obsession with fattening, dissecting, and searing turkeys, we almost inevitably pass up the fat-infused rear portion. According to Michael Carolan, professor of sociology and associate dean for research at the College for Liberal Arts at Colorado State University, that may have something to do with how Americans have traditionally perceived turkeys. Consumption was rare prior to World War II. When the birds were readily available, there was no demand for the tail because it had never been offered in the first place.

"Tails did and do not fit into what has become our culinary fascination with white meat," Carolan tells Mental Floss. "But also from a marketing [and] processor standpoint, if the consumer was just going to throw the tail away, or will not miss it if it was omitted, [suppliers] saw an opportunity to make additional money."

Indeed, the fact that Americans didn't have a taste for tail didn't prevent the poultry industry from moving on. Tails were being routed to Pacific Island consumers in the 1950s. Rich in protein and fat—a turkey tail is really a gland that produces oil used for grooming—suppliers were able to make use of the unwanted portion. And once consumers were exposed to it, they couldn't get enough.

“By 2007,” according to Carolan, “the average Samoan was consuming more than 44 pounds of turkey tails every year.” Perhaps not coincidentally, Samoans also have alarmingly high obesity rates of 75 percent. In an effort to stave off contributing factors, importing tails to the Islands was banned from 2007 until 2013, when it was argued that doing so violated World Trade Organization rules.

With tradition going hand-in-hand with commerce, poultry suppliers don’t really have a reason to try and change domestic consumer appetites for the tails. In preparing his research into the missing treat, Carolan says he had to search high and low before finally finding a source of tails at a Whole Foods that was about to discard them. "[You] can't expect the food to be accepted if people can't even find the piece!"

Unless the meat industry mounts a major campaign to shift American tastes, Thanksgiving will once again be filled with turkeys missing one of their juicier body parts.

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10 Juicy Facts About Sea Apples

They're both gorgeous and grotesque. Sea apples, a type of marine invertebrate, have dazzling purple, yellow, and blue color schemes streaking across their bodies. But some of their habits are rather R-rated. Here’s what you should know about these weird little creatures.


The world’s oceans are home to more than 1200 species of sea cucumber. Like sand dollars and starfish, sea cucumbers are echinoderms: brainless, spineless marine animals with skin-covered shells and a complex network of internal hydraulics that enables them to get around. Sea cucumbers can thrive in a range of oceanic habitats, from Arctic depths to tropical reefs. They're a fascinating group with colorful popular names, like the “burnt hot dog sea cucumber” (Holothuria edulis) and the sea pig (Scotoplanes globosa), a scavenger that’s been described as a “living vacuum cleaner.”


Sea apples have oval-shaped bodies and belong to the genus Pseudocolochirus and genus Paracacumaria. The animals are indigenous to the western Pacific, where they can be found shuffling across the ocean floor in shallow, coastal waters. Many different types are kept in captivity, but two species, Pseudocolochirus violaceus and Pseudocolochirus axiologus, have proven especially popular with aquarium hobbyists. Both species reside along the coastlines of Australia and Southeast Asia.


Sea cucumbers, the ocean's sanitation crew, eat by swallowing plankton, algae, and sandy detritus at one end of their bodies and then expelling clean, fresh sand out their other end. Sea apples use a different technique. A ring of mucus-covered tentacles around a sea apple's mouth snares floating bits of food, popping each bit into its mouth one at a time. In the process, the tentacles are covered with a fresh coat of sticky mucus, and the whole cycle repeats.


Sea apples' waving appendages can look delicious to predatory fish, so the echinoderms minimize the risk of attracting unwanted attention by doing most of their feeding at night. When those tentacles aren’t in use, they’re retracted into the body.


The rows of yellow protuberances running along the sides of this specimen are its feet. They allow sea apples to latch onto rocks and other hard surfaces while feeding. And if one of these feet gets severed, it can grow back.


Sea apples are poisonous, but a few marine freeloaders capitalize on this very quality. Some small fish have evolved to live inside the invertebrates' digestive tracts, mooching off the sea apples' meals and using their bodies for shelter. In a gross twist of evolution, fish gain entry through the back door, an orifice called the cloaca. In addition expelling waste, the cloaca absorbs fresh oxygen, meaning that sea apples/cucumbers essentially breathe through their anuses.


Most full-grown adult sea apples are around 3 to 8 inches long, but they can make themselves look twice as big if they need to escape a threat. By pulling extra water into their bodies, some can grow to the size of a volleyball, according to Advanced Aquarist. After puffing up, they can float on the current and away from danger. Some aquarists might mistake the robust display as a sign of optimum health, but it's usually a reaction to stress.


Sea apples use their vibrant appearance to broadcast that they’re packing a dangerous toxin. But to really scare off predators, they puke up some of their own innards. When an attacker gets too close, sea apples can expel various organs through their orifices, and some simultaneously unleash a cloud of the poison holothurin. In an aquarium, the holothurin doesn’t disperse as widely as it would in the sea, and it's been known to wipe out entire fish tanks.


These invertebrates reproduce sexually; females release eggs that are later fertilized by clouds of sperm emitted by the males. As many saltwater aquarium keepers know all too well, sea apple eggs are not suitable fish snacks—because they’re poisonous. Scientists have observed that, in Pseudocolochirus violaceus at least, the eggs develop into small, barrel-shaped larvae within two weeks of fertilization.


Syzgium grande is a coastal tree native to Southeast Asia whose informal name is "sea apple." When fully grown, they can stand more than 140 feet tall. Once a year, it produces attractive clusters of fuzzy white flowers and round green fruits, perhaps prompting its comparison to an apple tree.


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