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Where There's Muck, There's Beetles

Page history last edited by Tess Barrett 9 years, 1 month ago


Insects are, quite unjustifiably, objects of distaste to perhaps the majority of ordinary people. But the next time you are about to tread on a beetle, have mercy on it, not only because it will probably do you more good alive than dead but in recognition of its long interred ancestors, which are now being dug up and telling us how men lived in the distant past.


All through the history of archaeological excavation, diggers must have come across the shining, often brightly coloured, remains of insects as they trowlled through damp, dark coloured deposits on their sites. Before the middle 1960s these insects were either mentioned in the site report or, occasionally, a few were sent to an expert on of insects (an entomologist) to be properly indentified. More often, however they were totally ignored and we were robbed of one of the most important sources of evidence about conditions in the past. For every insect has a particular way of life and lives in a particular kind of place (although son called eurytopes, are less particular than others); like the boll weevil, it's got to have a home. If we can identify the insects found in an archaeological layer we can, working back through our knowledge of where they live at the present day (correctly, their habitats) say much about what was happening (in other words the ecological conditions) on the site when the layer formed, hundreds or thousands of years ago.


The serious study of the remains insects (which usually in fact means beetles, the Coleoptera) from archaeological sites was brought into its modern form by Peter Osborne, of the University of Birmingham, only about a decade ago. Since then several people who worked with Osborne while they were research students, including the writer, have been inspired by him to become involved in work on beetles in archaeology.

Many sites, including several in York, have been or are being studied and a great deal of exciting information has been obtained. The work in York is being carried out in the Environmental Laboratory of the York Archaeological Trust, the lab having been set up just over a year ago.


Insects are ubiquitous as everyone knows from personal experience. There are about 20,000 different species in Britain alone, nearly 4,000 of them beetles. All of them have more or less definite conditions which they need for their existence; not however, that we always know what those conditions are! Ignorance of the way of life of insects is one of the major problems which have to be faced when they are used in reconstructing the past. In fact, it seems that work on insects is providing a powerful stimulus for the improvement of ecological studies of living insects. The unfussy eurytope species have been mentioned and of course they have only limited use in archaeology. More useful are species with very restricted habitats, the stenotypes, which may need a particular plant as host or a very special kind of water or soil to live on.


On damp, waterlogged sites, where the lack of aeration in the deposits has caused any organic matter to become ‘reduced’ (black and smelly), any insects, together with seeds and other biological remains which somehow entered the deposit while it was forming, will be more or less well preserved. The insects which the excavator notices while he is digging are just the tip of an Iceberg in terms both of numbers and variety. Most insects are very minute and unnoticeable to the field archaeologists but in some cases hundreds, thousands, or under exceptional circumstances, millions, of insect corpses can be recovered from a few kilogrammes of the right kind of deposit by laboratory treatment. In this, the insects are extracted by fine sieves and a concentrating process known as paraffin flotation.They are picked out from the concentrate under the microscope and preserved in alcohol or on special card slides.


Having found a deposit which contains insect remains, in a situation in which the study of those remains can give useful information, and having extracted them, the real problems start. The insects belong to the great group of invertebrate animals called the Arthropoda. That is, they do not have an internal skeleton like fish or mammals, but an external jointed armour, or exoskeleton. This is composed mainly of sclerotin, a very tough protein much like the hair protein of man, together with a substance called chitin. The latter is very resistant to decay as only a few kinds of bacteria and fungi can break it down, and then only in the presence of oxygen from the air.


It is mainly due to the presence of the chitin that insects keep their shape and even colour after hundreds of years buried in the ground. It is also, of course, why insects can be preserved dry, on pins or stuck to cards, in campus collections. However, in order to move the insect must have flexible joints (the name Arthropoda means ‘jointed legs’) and these obviously cannot be strongly armoured. In fact not only the legs are jointed, for the body is formed of a series of rings also. This means that when the insect rots after death the exoskeleton breaks into many small plates, each called a sclerite. In Figure 1 a beetle, Cercyon atomarius, as shown as it appears alive or dried in a collection, together with the more important of the parts into which it breaks on decay. It is obvious that these bits cannot be identifiers as easily as the whole insects, which are often difficult enough to name in any case! Nor can they be recognised by the same characteristics, many of the parts having disappeared. In fact they can only be named by comparing each sclerite with the same part of a whole insect from a collection. This is very slow and tedious and requires a considerable knowledge of insects, but is a fascinating and challenging process, with all the appeal of a three dimensional jigsaw puzzle. Sometimes specimens are found which have not entirely fallen to pieces and occasionally the intromissive organs of the male, very distinctive and helpful in distinguishing similar species, can be dissected from inside the abdomen.


We have said that the majority of identifiable insects from archaeological sites are beetles. In fact perhaps 75% to 95% of all the insect remains recovered belong to this group, with the immature stages of flies (Diptera) often running a close second in abundance. The beetles give most information for they have been better studied by naturalists than most other insects. Many other kinds of insects have been found in smaller numbers, including human fleas, honey bees, froghoppers, earwigs and parasitic wasps; all of these have been found in samples taken from the Lloyd’s Bank site in York. Other arthropod remains may be found, especially mites, false scorpions and, where ditch deposits and others formed under water are concerned, water fleas.


So far the uses to which insects are put in archaeology have only been hinted at. The best way to show their value is through some examples. One very spectacular, but simple, case is that of W. H. Smith site at Coney Street, York, recently excavated by the Trust. In a trench dug within the cellar of a building, a layer was discovered which contained a great deal of grain, associated with timbers. This was provisionally interpreted as the remains of a grain store. Below this was a thick clay layer, which in turn covered a very thin layer of very amok organic silt. This second layer contained no detectable grain, but even during excavation large numbers of beetles were noticed in lumps taken from it. When a sample was taken to the laboratory and examined under the microscope it was found to contain immense numbers of beetles of kinds which could only live together in very spoiled grain. This layer, for which no remains of cereals had been recovered, clearly formed below an earlier grain store, no certain evidence of which could be obtained by conventional excavation methods. It has been roughly calculated that over a million insects were present in each square metre of this thin layer - the amount of grain destroyed to produce such an immense population must have been substantial.


A larger scale study of Insect remains with less immediate impact but wider implications has been carried out on samples taken from the many layers of highly organic deposits at Lloyd’s Bank site, York. On the basis of the archaeological evidence these are believed to be a succession of floor layers formed over many years within a building (probably a series of buildings) of Anglo-Scandinavian date serving as a leather workshop. A major study of the plant and animal remains is almost completed and shows what conditions must have been like within this building, as well as something of the activities carried out by its occupants. The insects, mainly beetles, show that without doubt the floors were, by modern standards, quite disgusting, for the majority of the beetles would be most at home together in a compost heaps! It is not possible to go into great detail here, but a number of beetles which only occur beneath plants of heather or ling suggest that these plants were being brought to the site. Further insect species may have been imported with bundles of reeds which were strewn on the floor. One tiny weevil, with a disproportionally long name Apion kiesenwetteri (also known as A. difficile), which was found in several of the floor layers, is supposed only to live on Dyers’ Greenweed, a plant which perhaps may have been used for colouring the wares made by the occupants.



Both the examples disclosed have been of deposits which formed inside (or perhaps beneath) buildings. There is little doubt that the vast majority of the insects found in the samples actually lived within the building and that most of the remainder were brought in accidentally by man. If deposits which formed in the open air are being studied the problems of deciding how the insects got into the material are more complicated. It has only recently been shown by the writer that large numbers of insects of many kinds may land on any open surface and that insects, which include many beetles, may have flown a considerable distance before arriving at the spot where they die. This means that as well as the insects which lived near to the site, which can tell us so much about conditions on it, the samples from archaeological layers studied in the laboratory may contain a large proportion of Insects which lived further away. These form a ‘background noise’ which will obscure the message. This discovery has introduced a new dimension into the study or insects in archaeology and much research must be carried out to overcome the problems it has thrown up.


All insects pass through a series of stages as they grow, either from the egg through a larva (grub, caterpillar, maggot) and pupa (the chrysalis of a butterfly or the ‘egg’ or an ant) to the breeding adult stage (this is the case with beetles, butterflies and moths, flies etc); or from egg to a ‘nymph’, which looks like a miniature wingless adults, then direct to the adult (in bugs. earwigs. dragonflies etc). The life cycle of a beetle, Anobium punctatum, the 'woodworm', is shown in Figure 2. Each of the stages or development is more or less distinctive in different species and can often be recognised when alive or preserved in alcohol. The immature stages of most insects are very soft, with only a few small armour plates, and so they are rarely found well preserved in the deposits on archaeological sites. Often, though, the hard ‘head capsules’ of beetle larvae survive and while they can rarely be named yet, further hard work using comparison with collections of modern named specimens may allow them to be identified and used as proof that particular beetles were actually breeding on the spot.



It is quite obvious that we can get a large amount of information from studies of insects in archaeology, but this work should not be carried out in isolation. It must be related to all the other kinds or evidence that recorded in the field as well as from botanical and other laboratory work. Take, for example, the case of the beetles associated with heather which were recovered from the Lloyd’s Bunk site - how do we know that they did not arrive flying? Small amounts of heather twigs, by themselves not adequate evidence, combine with the beetle remains to remains to make a consistent story of the import of quite large amounts of heather or ling in which a few insects accidentally remained trapped. The presence of a small number of water beetles at the one site does not mean that the building was under water - they either flew in (certain water beetles fly very readily In order to colonise new ponds) or they were brought in with buckets of water or amongst the roots of reeds which were thrown on to the floor. In fact the latter possibility is most favoured, for some beetles which live on marsh plants have been identified, together with many seeds of swamp plants, while small amounts of reed stem were noted in some layers during the day. Here again several pieces of evidence combine to support one line of deduction.


Work on ancient insects is not confined to town sites or those directly related to man. Studies of the beetles of both natural deposits and those developed in association with men (as is the case of the York sites) combine to show that dramatic changes have occurred in the abundance and geographical ranges of many insect species during the past few thousand years. A few examples of species which were once common but are now rare have come out of the York studies, while several beetles found in ‘natural’ deposits in Yorkshire are now extinct in Britain or not found so far north. Men must take most of the responsibility. In towns the changes are due to different building methods and gradual (and very necessary) improvements in hygiene standards, while in the countryside they have been caused by the wholesale destruction of forests and other natural habitats. We are still energetically and often needlessly destroying the natural world around us. As well as giving archaeologists (and also climatologists) new sources of information, the study of ancient insects has provided a broader lesson: it has underlined the importance of man in changing the natural environment, a complex integrated system which once destroyed to the certain long term detriment of men, can never be replaced.


Harry Kenward



Further reading: 2 articles in Science and Archaeology (published by George Street Press, Fancy Walk, Stafford), by P. J. Osborne, vol 10, pp. 4 and 6; by H. Kenward, vol 13, pp. 16-24, give an introduction to the subject and have useful bibliographies. An article by P.C. Buckland in Journal of Archaeological Science, vol 1, pp 303-316, discusses interesting aspects of York s ancient environment.  

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