Chasing Bookworms: What Missing Art Can Tell You About Insects

"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.

Photo Illustration by Mental Floss. Curie: Hulton Archive, Getty Images. Background: iStock
10 Radiant Facts About Marie Curie
Photo Illustration by Mental Floss. Curie: Hulton Archive, Getty Images. Background: iStock
Photo Illustration by Mental Floss. Curie: Hulton Archive, Getty Images. Background: iStock

Born Maria Salomea Skłodowska in Poland in 1867, Marie Curie grew up to become one of the most noteworthy scientists of all time. Her long list of accolades is proof of her far-reaching influence, but not every stride she made in the fields of chemistry, physics, and medicine was recognized with an award. Here are some facts you might not know about the iconic researcher.


Maria Skłodowska was the fifth and youngest child of two Polish educators. Her parents placed a high value on learning and insisted all their children—even their daughters—receive a quality education at home and at school. Maria received extra science training from her father, and when she graduated from high school at age 15, she was first in her class.


After collecting her high school diploma, Maria had hoped to study at the University of Warsaw with her sister, Bronia. Because the school didn't accept women, the siblings instead enrolled at the Flying University, a Polish college that welcomed female students. It was still illegal for women to receive higher education at the time so the institution was constantly changing locations to avoid detection from authorities. In 1891 she moved to Paris to live with her sister, where she enrolled at the Sorbonne to continue her education.


Marie Curie and her husband, Pierre Curie, in 1902.
Marie Curie and her husband, Pierre Curie, in 1902.
Agence France Presse, Getty Images

In 1903, Marie Curie made history when she won the Nobel Prize in physics with her husband, Pierre, and with physicist Henri Becquerel for their work on radioactivity, making her the first woman to receive the honor. The second Nobel Prize she took home in 1911 was even more historic. With that win in the chemistry category, she became the first person of any gender to win the award twice. She remains the only person to ever receive Nobel Prizes for two different sciences.


The second Nobel Prize she received recognized her discovery and research of two elements: radium and polonium. The former element was named for the Latin word for "ray" and the latter was a nod to her home country, Poland.


Marie Curie's daughter Irène Joliot-Curie, and her husband, Frédéric Joliot-Curie, circa 1940.
Marie Curie's daughter Irène Joliot-Curie, and her husband, Frédéric Joliot-Curie, circa 1940.
Central Press, Hulton Archive // Getty Images

When Marie Curie and her husband, Pierre, won their Nobel Prize in 1903, their daughter Irène was only 6 years old. She would grow up to follow in her parents' footsteps by jointly winning the Nobel Prize for chemistry with her husband, Frédéric Joliot-Curie, in 1935. They were recognized for their discovery of "artificial" radioactivity, a breakthrough made possible by Irène's parents years earlier. Marie and Pierre's other son-in-law, Henry Labouisse, who married their younger daughter, Ève Curie, accepted a Nobel Prize for Peace on behalf of UNICEF, of which he was the executive director, in 1965. This brought the family's total up to five.


The research that won Marie Curie her first Nobel Prize required hours of physical labor. In order to prove they had discovered new elements, she and her husband had to produce numerous examples of them by breaking down ore into its chemical components. Their regular labs weren't big enough to accommodate the process, so they moved their work into an old shed behind the school where Pierre worked. According to Curie, the space was a hothouse in the summer and drafty in the winter, with a glass roof that didn't fully protect them from the rain. After the famed German chemist Wilhelm Ostwald visited the Curies' shed to see the place where radium was discovered, he described it as being "a cross between a stable and a potato shed, and if I had not seen the worktable and items of chemical apparatus, I would have thought that I was been played a practical joke."


Marie Curie's journals
Hulton Archive, Getty Images

When Marie was performing her most important research on radiation in the early 20th century, she had no idea the effects it would have on her health. It wasn't unusual for her to walk around her lab with bottles of polonium and radium in her pockets. She even described storing the radioactive material out in the open in her autobiography. "One of our joys was to go into our workroom at night; we then perceived on all sides the feebly luminous silhouettes of the bottles of capsules containing our products[…] The glowing tubes looked like faint, fairy lights."

It's no surprise then that Marie Curie died of aplastic anemia, likely caused by prolonged exposure to radiation, in 1934. Even her notebooks are still radioactive a century later. Today they're stored in lead-lined boxes, and will likely remain radioactive for another 1500 years.


Marie Curie had only been a double-Nobel Laureate for a few years when she considered parting ways with her medals. At the start of World War I, France put out a call for gold to fund the war effort, so Curie offered to have her two medals melted down. When bank officials refused to accept them, she settled for donating her prize money to purchase war bonds.


Marie Curie circa 1930
Marie Curie, circa 1930.
Keystone, Getty Images

Her desire to help her adopted country fight the new war didn't end there. After making the donation, she developed an interest in x-rays—not a far jump from her previous work with radium—and it didn't take her long to realize that the emerging technology could be used to aid soldiers on the battlefield. Curie convinced the French government to name her Director of the Red Cross Radiology Service and persuaded her wealthy friends to fund her idea for a mobile x-ray machine. She learned to drive and operate the vehicle herself and treated wounded soldiers at the Battle of the Marne, ignoring protests from skeptical military doctors. Her invention was proven effective at saving lives, and ultimately 20 "petite Curies," as the x-ray machines were called, were built for the war.


Following World War I, Marie Curie embarked on a different fundraising mission, this time with the goal of supporting her research centers in Paris and Warsaw. Curie's radium institutes were the site of important work, like the discovery of a new element, francium, by Marguerite Perey, and the development of artificial radioactivity by Irène and Frederic Joliot-Curie. The centers, now known as Institut Curie, are still used as spaces for vital cancer treatment research today.

Big Questions
Where Did the Myth That Radiation Glows Green Come From?

by C Stuart Hardwick

Probably from radium, which was widely used in self-luminous paint starting in 1908. When mixed with phosphorescent copper-doped zinc sulfide, radium emits a characteristic green glow:


The use of radioluminescent paint was mostly phased out by the mid-1960s. Today, in applications where it is warranted (like spacecraft instrument dials and certain types of sensors, for example), the radiation source is tritium (radioactive hydrogen) or an isotope of promethium, either of which has a vastly shorter half life than radium.

In most consumer products, though, radioluminescence has been replaced by photoluminescence, phosphors that emit light of one frequency after absorbing photons of a difference frequency. Glow-in-the-dark items that recharge to full brightness after brief exposure to sunlight or a fluorescent light only to dim again over a couple of hours are photoluminescent, and contain no radiation.

An aside on aging radium: By now, most radium paint manufactured early in the 20th century has lost most of its glow, but it’s still radioactive. The isotope of radium used has a half life of 1200 years, but the chemical phosphor that makes it glow has broken down from the constant radiation—so if you have luminescent antiques that barely glow, you might want to have them tested with a Geiger counter and take appropriate precautions. The radiation emitted is completely harmless as long as you don’t ingest or inhale the radium—in which case it becomes a serious cancer risk. So as the tell-tale glow continues to fade, how will you prevent your ancient watch dial or whatever from deteriorating and contaminating your great, great grandchildren’s home, or ending up in a landfill and in the local water supply?

Even without the phosphor, pure radium emits enough alpha particles to excite nitrogen in the air, causing it to glow. The color isn’t green, through, but a pale blue similar to that of an electric arc.


This glow (though not the color) entered the public consciousness through this early illustration of its appearance in Marie Curie’s lab, and became confused with the green glow of radium paints.

The myth is likely kept alive by the phenomenon of Cherenkov glow, which arises when a charged particle (such as an electron or proton) from submerged sources exceeds the local speed of light through the surrounding water.

So in reality, some radionuclides do glow (notably radium and actinium), but not as brightly or in the color people think. Plutonium doesn’t, no matter what Homer Simpson thinks, unless it’s Pu-238—which has such a short half life, it heats itself red hot.


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