What’s in a pot? – Understanding the past through fossilised insects

We’re celebrating National Insect Week with a blog from insect archaeologist Dr Eva Panagiotakopulu from the University of Edinburgh about how insect remains are shedding light on the history of civilisation.

In the present day, with pest invasions, increasing concern over declines in insect populations, and the homogenisation of environments as a result of human impact, looking at the past provides an important perspective on change.

Fossilised insects from archaeological and geological deposits are often identifiable to species and as each has particular habitat requirements it is possible to reconstruct past environments. This provides essential information on environmental change, ranging from broad patterns of biogeography to specific detail on individual contexts.

Fig 1 Sitophilus granarius charred
Charred Sitophilus granarius – the granary weevil

Considering human movement and accidental introductions, there are interesting stories being revealed which map the itineraries of early groups, hunter gatherers and farmers on sites ranging from the Egyptian desert to the Arctic fringe.

Take for example the main pest of cereals, the granary weevil – (Sitophilus granarius). It probably moved from the nests of rodents feeding on stores of wild grasses to early storage areas in the Fertile Crescent, and has progressively become cosmopolitan. Its earliest fossil record comes from the Levantine coast and, although flightless, it hitched lifts to the Aegean, where it occurs at Santorini in modern day Greece.

800px-Map_of_fertile_crescent.svg
The Fertile Crescent is a region of the middle east where early civilisations flourished

 

From there, it moved to Central Europe, in the footsteps of the first farmers of the Linear Pottery culture groups, eating away cereals in their storerooms, and no doubt contributing to the occasional local famine.

After a hiatus, it joins the Roman army and its supply chains and large granaries extending north to the Antonine Wall in Scotland and the Rhine Frontier.  The collapse of Roman power may have led to another hiatus but in the medieval period Norse expansion took it to remote islands in northern Norway and to Iceland, but interestingly not Greenland, where its absence is shared by dung beetles.

A similar pattern of expansion applies to a range of species, responsible for extensive losses of crops in storage and also to species, which are linked directly or indirectly with the spread of disease – house flies and human fleas immediately come to mind. Their distribution over time mirrors cultural change, ecological imperialism and the development of levels of complexity which have led to the modern loss of biogeographic barriers and global spread of pests and epidemics.

The details from individual contexts give fascinating insights, in particular where preservation is optimal, as in the desiccating conditions of the Egyptian desert. It is a unique moment when in a 6th century ceramic jar from an early Christian site near Aswan, Qasr Ibrim, there are around 9000 individuals of the saw-toothed merchant grain beetle (Oryzaephilus mercator), a pest with a preference for infesting nuts and oilseeds.

O. mercator.jpg
Oryzaephilus mercator, the merchant grain beetle

 

Entomologists have suggested that the species is of sub-Saharan African origin, perhaps invading Egypt via the Nile valley, but one only has to look at the name of its congener – Oryzaephilus surinamensis – freely translated as the rice-loving weevil from Surinam  to see how wrong one can be without recourse to the fossil record.  The latter occurs frequently with the grain weevil in burnt Roman grain residues and is now equally cosmopolitan.

The Qasr Ibrim finds are the merchant grain beetle’s first archaeological record and an essential part of the puzzle to understand its distribution. The insects were found infesting radish seeds, presumably used in cooking or to be crushed for their oil, cheaper than olive oil; they were just a bit of additional protein in the final product, although too many can be poison.

 

Fig 5 Trogoderma granarium.jpg
Trogoderma granarium, The Khapra Beetle

A few examples of the khapra beetle, Trogoderma granarium, appear in the same sample. Prevailing entomological opinion is that this serious pest of stored grain in the warmer parts of the world is of Indian or South East Asian origin – and this may be the case, having arrived in Egypt via trade across the Indian Ocean. Although only more work on fossil material will tell.

References
Panagiotakopulu, E., Buckland, P. C. (2017). A thousand bites: Insect introductions and late Holocene environments. Quaternary Science Reviews 156, 23-35.

 

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