What archaeological insects tell us about our past

• Insects react to disturbances in their environment (whether due to human practices or natural phenomena) and are therefore "bio-indicators of the environment", according to our partner The Conversation.

• But if insects help us to study our current environment, they can also allow us to understand that of our ancestors and the relationships that they maintained with their natural environment or modified by their actions.

• This analysis was conducted by Jérémy Rollin, doctoral student in archaeoentomology at the University of Tours.

They are everywhere !

In the house, the garden or the forest, insects have conquered all the ecological niches.

So nothing surprising if you see them every day.

If you look closely, you will see that they are not the same depending on the location.

Although they are present in all environments, many insects have strict requirements vis-à-vis their living conditions.

These can be based on physico-chemical balances (temperature, humidity, etc.), on the availability of a food resource, or even on the degree of light in an environment (forest, meadow, etc.).

Their presence is therefore conditioned by many environmental factors.

Consequently, insects react to disturbances in their environment, whether due to human practices or natural phenomena – insects are thus “bio-indicators of the environment”.

But if insects help us to study our current environment, they can also allow us to understand that of our ancestors and the relationships that they maintained with their natural environment or modified by their actions.

​Remains of archaeological insects

Archaeoentomology is the discipline that studies the remains of insects from archaeological sites.

Having not undergone any evolution for the last hundred millennia, archaeological insects are therefore comparable to modern insects.

It is by relying on this observation that scientists are able to identify them.

This is possible thanks to their exoskeleton, that is to say their shell, in particular that of beetles (beetles, ladybirds, etc.), which is more resistant and can be kept for long periods without being fossilized.

Like the bones from archaeological excavations, the insects will be preserved in their current state, but in the form of more or less degraded fragments called “sclerites”.

Their state of conservation varies according to the burial medium.

They can be dry and confined environments such as tombs, or charred structures such as granaries and silos, but it is the humid environments that are most conducive to their good conservation (wells, moats, peat bogs, etc.).

To extract the remains of insects from an archaeological layer, the sediment taken from the field is gently disintegrated in a basin under a jet of water, then sieved.

The organic remains are then soaked in dearomatized petroleum – to which the insects' exoskeleton adheres, unlike plant debris: this step makes it possible to isolate the insect remains.

Once the remains of insects have been extracted and sorted, we begin by identifying them with the species, genera or families for each sample, each corresponding to a precise dating.

Then, then we interpret the ecological role of each of these insects in this environment.

Thus, it is possible to obtain information on past societies, the environmental conditions of the time, or even on the way in which human activities have shaped the environments.

But it is also possible to address ecological questions on the first invasive insects or the first impacts of humans on biodiversity.

​Insects that bear witness to paleoclimates and paleoenvironments

In France, there are more than 11,000 species of beetles adapted to a diversity of habitats.

The climatic conditions control the geographical distribution of many beetles, in particular the predators called “beetles” – the presence of one species or another in the archaeological sediment therefore gives indications of the climate which reigned at the time of the deposit.

In addition to the climate, insects can bring a lot of information on the environment and its evolution under the influence of human practices.

As such, phytophagous (vegetarians) and xylophagous (wood eaters) have a place of choice.

Some species only thrive in forest environments, unlike others that prefer open environments such as grasslands.

They will thus make it possible to obtain an image of the environment, as well as of its plant cover, because phytophagous depend on the presence of their host plant.

Among these specialized insects, the root beetle family perfectly illustrates this monophagy.

Indeed, there are many species, each adapted to a plant or plant family: birch beetle, alder, mint or even cabbage flea beetle... Their presence on an archaeological site means that the food plant was present, although it is not preserved in the majority of cases.

​Dung beetles testify to the beginning of soil amendment in the Iron Age

Nitrophile plants are those that like soil rich in nitrates and organic waste.

These plants, the most famous of which is undoubtedly the nettle, are often typical of environments exploited by humans, with animals in a pastoral context, for example.

Entomologically, this is reflected by the presence of these specialized phytophagous, but also by the presence of coprophages, the famous dung beetles.

These insects feed on the excrement of other animals and therefore play an essential role, because they recycle organic matter into natural fertilizer and at the same time prevent the spread of diseases in the natural environment and livestock.

Although the best known is the sacred beetle of the Egyptians, there are around 250 species of dung beetle in France with varying habits.

These species can make it possible to certify the presence of farms in forest or grassland environments as well as important historical phenomena such as the beginnings of soil amendment practices by manure in the Iron Age.

Additionally, some species appreciate a wide range of droppings while others are stricter.

Their requirements provide us with information about the animals that grazed, even if no bone remains are present.

If dung beetles and other decomposers are beneficial in farms, other insects are more problematic for the agricultural environment.

Even today, we fight against pests that cause damage to our crops and our stocks.

The history of these insects is closely linked to humans and the beginning of agriculture where these species moved from the natural environment to an anthropized environment where the abundance of food resources (monoculture, stocks, etc.) favored their outbreaks.

For archaeological research, these pests can provide information on the sanitary quality of foodstuffs as well as on repellent practices.

As such, the Roman agronomist Columelle offers advice on the height of piles of grain to be kept in granaries,

chapter 6).

​The wheat weevil as a witness to human migrations and trade routes

The wheat weevil (

) has been known since antiquity to cause serious damage to grain stocks.

This is a species that lays eggs and achieves its larval development in stored grain reserves (wheat, rye, barley, etc.) and therefore does not need the living plant to feed itself.

This insect has the particularity of being wingless, that is to say without wings, which makes it dependent on human migrations for its movements.

By accompanying grain transfers, his disability therefore gives him the privileged status of witness to long-distance grain transport and its intensification throughout history.

Originally from Asia Minor, it is possible to see its progression in the Near East from the Neolithic period (7000 BC) to Protohistory (2500 BC).

We then observe a very intense invasion of this insect in Roman times, from the moment when Gallo-Roman urbanization became massive (1st century AD), to finally arrive in America at the time modern (18th century).

​Insects bear witness to the impact of humans on biodiversity

Deforestation for agriculture and livestock, soil amendment or urbanization: by locally modifying natural ecosystems, these practices have had an impact on entomological biodiversity by favoring certain species to the detriment of others.

By comparing the same sites at different times, it is possible to see how certain insects were able to adapt to anthropized environments, then form the first communities of sinanthropic insects (living wild animals close to humans: flies, cockroaches, moths, etc. .);

while others must have moved away or become locally extinct as a result of habitat destruction (plum-pecker).

In the same vein, the growth in trade in goods, foreign foodstuffs or even new animals from the Iron Age could have allowed the introduction of invasive insects and parasites into a new environment.

This scenario would follow the trail of the arrival of the black rat in France in the 1st century AD.

J.-C. or weeds (weeds) such as corn cockle and myagre which would have followed human transport in the Iron Age.

Our "ARCHAEOLOGY" file

As we begin to understand the mechanisms of biological invasions and their impacts on the environment, could it be imagined that past practices had to adapt to insects not yet identified?

Only the analysis of insects from many other sites will allow us to better understand the evolution of interactions between humans and their environment throughout history.

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This analysis was written by Jérémy Rollin, doctoral student in archaeoentomology at the University of Tours.

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