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Animal Antics: Fossils in ancient books surprise researchers

By MELANIE HSU | November 29, 2012

For those who love fossils but lack the time or stamina to dig through the dirt, try checking out some medieval library books — and be careful not to breathe in all the dust! A recent study reported that white spots found in some of these old books are actually fossil records of European beetles. Each of them is actually a wormhole, the result of hatching beetles chewing through the woodblocks used to print arts and illustrations between the 1400s and 1800s. And you thought that bookworm infestations were scary!

These literary fossils reveal that the population distribution of two species of beetle, the common furniture beetle (Anobium punctatum) and the Mediterranean furniture beetle (Oligomerus ptilinoides), have changed over time. While they were once separate, these beetles now share overlapping regions in Western Europe. According to study researcher Blair Hedges, a biologist at Pennsylvania State University, these wormholes were central to uncovering the history of these beetles.

In the 1400s, European printers began using carved wood blocks, or woodcuts, to produce printed illustrations. Unfortunately for the printers, the hardwood that was used for these blocks happened to be delicacy for certain species of beetles, which left their larvae to lodge in the wood. Once the larvae matured into beetles, the newborns ate their way out, leaving behind round holes in the literature.

As these woodcuts became increasingly infested, the number of white dots in books increased as well. The silver lining for researchers, however, was that these holes became a good indication of where these beetles lived at any given time. Hedges says that these wormholes are about the best fossils one could ever hope to find, as the literature provided exact dates and locations.

By examining medieval tomes in library collections, as well as in online, high-resolution, digital archives, Hedges was able to investigate the white spots. In a sample of 473 prints dating from 1462 to 1899, he discovered thousands of spots. Among these findings were no less than 3,263 perfectly round holes, created when the beetles escaped from the wood block, and 318 meandering tracks, which were made when they chewed along the wood grain. These tracks are called trace fossils.

In addition, Hedges found that the sizes of these holes differed by area, and from this, he was able to create a distribution map of different species of beetles. In northern cities such as London, the books tended to have small holes, which averaged about 0.06 inches across. In southern European cities, they averaged about 0.09 inches across. The larger holes were created by the common furniture beetle, while the smaller ones were left behind by Mediterranean furniture beetles, respectively.

At that time, these two species of beetle did not enjoy each other’s company. They resided on opposite sides of a border that cut across France, between Switzerland and Germany, and finally between Italy and Austria. Interestingly, their regions were very close to overlapping – in fact, the bugs lived only a few miles apart.

Hedges says that this kind of species distribution, where two species are separated by a boundary, is very uncommon. He speculates that the beetles remained separate due to an effort to avoid competition, as both species prefer to dine on the same kind of wood.

Today, thanks to our own rapidly proliferating species, these boundaries no longer exist. Due to increased furniture and lumber trades, both beetles can be found throughout Western Europe, happily chewing through libraries everywhere (I exaggerate, of course). The situation in Eastern Europe, according to Hedges, is a bit more complex.

Hedges, who published his findings in the journal Biology Letters on November 20, says that there is a lot of potential for taking this research further. For one, Japan and China started woodcut printings earlier than Europe, so there is a good chance of discovering more species and interactions.

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