It’s high time we cleaned out our gutters, to get ready for the coming fire season, which might be a bad one. The cockies help, digging out some moss from time to time, but it needs to be done properly.
What has this to do with insects?
Well, therein lies a tale…
In Britain in the 1950s, archaeology became refined. The digs were done more carefully, sifting through layer by layer for all evidence. Similar techniques were used for organic deposits from the glacial and interglacial periods of the last million years. These techniques produced bits of insects, particularly beetles, because beetles are particularly thick shelled.
The shell (or exoskeleton) of a beetle is like a natural plastic, composed of stable polymers of organic compounds, which can last for a long time, long after the insect has died. Of course, it depends on climate and what else is around (bacteria, fungi, chemicals) that might eat such bits, but the hard parts of beetles are known to last for up to two years in surface leaf litter. Once they are deep in soil they can last longer, because there’s less around to damage them.
So the British archaeologists were finding these fragments. Insect fragments can be pretty hard to identify, especially here, where the fauna is so poorly known, but in Britain all beetles are well-known and it was realised that these fragments could be identified to species.
For example, it was found that the Roman sewers in York contained dung beetles that are only found in southern Europe nowadays, showing that the climate 2000 years ago was warmer (than the 1950s, maybe not now!).
And, conversely, beetles that are only known from Siberia nowadays were found in post-glacial deposits in Britain, showing that the climate was much cooler.
All well and good. But, since many beetle species are restricted in habitat, it was realised that local habitats could be reconstructed from the fragments in archaeological digs. So, for a while, sites were described as being next to an oak forest or similar.
But an archaeologist in York wasn’t convinced. He took a sample from the gutter of his house in central York and had it analysed as if from a dig. The analysis showed that he lived beside a peat bog!
What was going on? Well, many insects fly, especially wetland insects because their homes can dry out so they need to find new sites. And these insects form a kind of aerial plankton, which in this case might have landed on a wet slate roof, mistaking it for a bog.
Insect bits are still used to help analyse archaeological sites, but with caution. And if you know your insects bits, you can use them for forensic science, or analysis of bird feeding, or study of insect fragments in foods.
It’s a useful skill.
Illustration above by Alexander Henry Halliday, 1852, thanks to Wikicommons
