Friday, 23 November 2012

Learning about beetles from old books

What can you discover about beetles by studying mediæval books?  Well as it turns out, there's one thing you might be surprised by.

This article on the Discover blog, reports the findings of an evolutionary biologist, one Blair Hedges, from Pennsylvania State University.

Hedges examined woodblock illustrations in books printed in Europe between 1462 and 1899, and measured 3,200 beetle holes.

Between these dates, many books were illustrated with woodblock engravings, and what was new to me (despite being rather obvious) is that when the wood was engraved, it had no visible wormholes, but it did have beetle larvae living inside, so some time after the engraving was finished, adult beetles would emerge, leaving a misnamed wormhole.  We assume it was too expensive to throw the block away, so pictures were printed with white circles marking where the beetles had emerged.

Hedges found that there were two sizes of round hole, and that these pricisely matched two species of European furniture beetle, and only them.  The smaller holes were made by the northern furniture beetle and the larger ones by the Mediterranean furniture beetle.

OK, that's not terribly exciting, though it is novel.  But if you check out where the books were printed, you find that the two species were distributed quite separately, with a clear demarkation line between them.  Presumably the northern species liked it cooler and wetter, while the southern species liked it hotter and drier.

Until now.  These days, the northern furniture beetle is found all the way south to the Mediterranean, and the Mediteranean furniture beetle is found all the way up to northern France and Germany.  It hasn't made it to the UK or Scandinavia yet, as far as we know.

The speculation is that the protected environment inside our houses has allowed the beetles to extend their territories hugely.

And all discovered by measuring printing defects in old books!

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