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Chasing Bookworms: What Missing Art Can Tell You About Insects

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"The Rich Man" by Cornelis Anthonisz (1541), courtesy Rijksmuseum, Amsterdam.

Between the 15th and 19th centuries, Europeans illustrated their books mainly with woodcuts. A woodcutter would etch a block of wood with an image so that when the block was dipped in ink and then stamped on a page, the areas that were cut away would leave just the white paper, and the remaining raised parts would pick up the ink and create black lines. (Here’s Albrecht Dürer’s Samson Rending the Lion as woodblock and ink-on-paper).

Those carved-out parts of the blocks and the white spaces on the paper were just as important to the art as the untouched wood and lines of ink. Empty spaces can say a lot. That’s why Blair Hedges, an evolutionary biologist at Pennsylvania State University, is so interested in certain holes that appear in many of these old books.

Bugging Out

These aren’t holes in the plots, but the artwork. Called wormholes, they’re actually the handiwork of beetles which came from eggs laid in trees and then emerged from the wood as adults, sometimes after the trees were turned into lumber—and sometimes even after a piece of wood had been carved with an image for printing. Hiring an illustrator to remake blocks affected by the bugs was expensive, so printers often went ahead and used them anyway, and many woodcut illustrations in older books are pockmarked with small circles that interrupt the ink lines. You can see some in the image above.

To biologists, those circles are trace fossils. Like a tooth mark or a footprint, they provide evidence that an animal was in a given place at one time. In this case, they pinpoint where a beetle once burst forth into the world. Hedges has used wormhole fossils from old books, maps, and art prints to study the distribution of certain wood-boring beetles over the hundreds of years when woodcuts were at the height of their use.

For a recently published study, he examined some 3000 wormholes in woodcut illustrations made between 1462 and 1899. He found that the wormholes in illustrations printed in northern Europe were round and, on average, 1.4 millimeters across. The wormholes from southern Europe were about twice as large, averaging 2.3 mm across. Many southern holes were also pill-shaped, or had “tracks” instead of being a a circle, shaped by the beetle exiting its nursery in a diagonal path instead of digging straight up and out (shown below).

Woodcut (1606) by Giovanni Battista Ramusio, courtesy Library of Congress

Going by the size and shape of the holes and what’s known about beetles’ wood preferences (some, for example, only lay their eggs in damp, rotting wood, which is not something that would be used in printing), Hedges was able to pin the holes in the illustrations on two species. He thinks the common furniture beetle (Anobium punctatum) is the likely culprit for the northern European works, and the Mediterranean furniture beetle (Oligomerus ptilinoides) for the southern ones.

Drawing the Line

The woodcut holes suggest a clear geographic divide between the beetles. Through hundreds of years of European literature and art, the two species’ ranges appear to have butted up against one another, but never overlapped.

This stark division is shocking because, today, both beetles are widely distributed through western, central, and southern Europe. There’s a lot of overlap in their ranges, and no one knew until now how their distribution was in the past, or if or how it had changed.

By looking at where and when the books were printed, Hedges was able to plot the historical dividing line between the two beetles (shown in the map below with each species’ current European range). Characteristics of its shape—like the curve south as it approaches France’s humid west coast—and the northern beetle’s sensitivity to certain environmental factors—like a combination of low humidity and high temperature—suggested to Hedges that the boundary between the two species was partly a matter of climate. As the climate changed over the centuries, though, the border might have held because both beetles prefer the same kind of wood, and they were avoiding competition with each other for it.

Broadening their Horizons

Top: historic range of two wood-boring beetles. Bottom L: modern range of the common furniture beetle. Bottom R: modern range of the Mediterranean furniture beetle. Hedges, 2012

The beetles expanded their range in the late 19th and early 20th centuries, which means that people are one reason for the fall of the dividing line, Hedges says. The beetles' expansion came during a time when increasing global trade, travel, and commerce moved infested wood around Europe and to other continents, and modern homes with carefully controlled climates might have allowed the bugs to acclimate to new areas and eventually colonize them.

And all that comes from some blank spaces in old drawings.

While the books told Hedges a lot about the beetles, he says that the beetles can teach us something about books. In situations where a book’s point of origin is unclear, he says, historians could now use the known historical range of these two beetles to determine whether a book was from northern or southern Europe, just by examining and measuring what the insects left behind.

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Health
Growing Up With Headphones May Not Damage Kids’ Hearing
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A study published in the American Medical Association's JAMA Otolaryngology-Head & Neck Surgery finds no increase in child and adolescent hearing loss despite a rise in headphone and earbud use.

"Hearing impairment in children is a major public health burden given its impact on early speech and language development, and subsequently on academic and workforce performance later in life," the authors write. "Even mild levels of hearing loss have been found to negatively affect educational outcomes and social functioning."

As portable music players continue to grow in popularity, parents, doctors, and researchers have begun to worry that all the music pouring directly into kids' ears could be damaging their health. It seems a reasonable enough concern, and some studies on American kids' hearing have identified more hearing loss.

To take a closer look, researchers at the University of California-San Francisco analyzed data from the National Health and Nutrition Examination Survey (NHANES), collected from 1988 to 2010. They reviewed records from 7036 kids and teens between the ages of 12 and 19, checking each participant's hearing tests against their exposure to noise.

As expected, the authors write, they did find a gradual increase in headphone use and other "recreational noise exposure." And they did see an uptick in hearing loss from 1988 to 2008 from 17 percent to 22.5 percent. But after that, the trend seemed to reverse, sinking all the way down to 15.2 percent—lower than 1988 levels. They also found no significant relationship between noise exposure and hearing loss.

The results were not uniform; some groups of kids were worse off than others. Participants who identified as nonwhite, and those of lower socioeconomic status, were more likely to have hearing problems, but the researchers can't say for sure why that is. "Ongoing monitoring of hearing loss in this population is necessary," they write, "to elucidate long-term trends and identify targets for intervention."

Before you go wild blasting music, we should mention that this study has some major limitations. Hearing loss and other data points were not measured the same way through the entire data collection period. Participants had to self-report things like hearing loss and health care use—elements that are routinely under-reported in surveys. As with just about any health research, more studies are still needed to confirm these findings.

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Weather Watch
NASA Figures Out Why When It Rains, It (Sometimes) Drizzles
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What’s the difference between drizzle and rain? It has to do with updrafts, according to new research by NASA scientists into the previously unexplained phenomenon of why drizzle occurs where it does.

The answer, published in the Quarterly Journal of the Royal Meteorological Society, could help improve how weather and climate models treat rainfall, making predictions more accurate.

Previously, climate researchers thought that drizzle could be explained by the presence of aerosols in the atmosphere. The microscopic particles are present in greater quantities over land than over the ocean, and by that logic, there should be more drizzle over land than over the ocean. But that's not the case, as Hanii Takahashi and her colleagues at the Jet Propulsion Laboratory found. Instead, whether or not rain becomes full droplets or stays as a fine drizzle depends on updrafts—a warm current of air that rises from the ground.

Stronger updrafts keep drizzle droplets (which are four times smaller than a raindrop) floating inside a cloud longer, allowing them to grow into full-sized rain drops that fall to the ground in the splatters we all know and love. In weaker updrafts, though, the precipitation falls before the drops form, as that light drizzle. That explains why it drizzles more over the ocean than over land—because updrafts are weaker over the ocean. A low-lying cloud over the ocean is more likely to produce drizzle than a low-lying cloud over land, which will probably produce rain.

This could have an impact on climate modeling as well as short-term weather forecasts. Current models make it difficult to model future surface temperatures of the Earth while still maintaining accurate projections about the amount of precipitation. Right now, most models that project realistic surface temperatures predict an unrealistic amount of drizzle in the future, according to a NASA statement. This finding could bring those predictions back down to a more realistic level.

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