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THE ORIGIN OF FLYING INSECTS.

Insects, like other invertebrates, have been preserved in a fossil state due to a series of events that has resulted in their burial in an appropriate medium. An immediate burial is needed for the whole insect to be preserved.  Any other way and the body becomes soft and all its parts fall away, often leaving only the wings. These decompose more slowly and therefore, can be preserved in less favourable conditions. For this reason, many examples of fossilized insects consist only of the wings. Moreover, insect fossils are not found in as many deposits or sites as the majority of other arthropods. 

Insect fossils have been found in nearly 150 places in different parts of the world.  Commentry, in Central France, can be considered to be among the most important. Here, in a freshwater lake, thousands of more or less well preserved specimens were deposited in the late Carboniferous Period (approx. 3000 million years ago) and are thought by some to be the oldest known insects. Another site of considerable importance is the Elmo limestone, in the state of Kansas, USA. Until now, almost 10,000 insects, both aquatic and crustacean have been found, admirably well preserved. The lithographic limestone of Bavaria and others of the same kind, mainly distributed around Europe, have provided very valuable materiel for the investigators but, no other deposit surpasses in riches the marvellous Baltic Amber, on the German coast, to which material we will refer to as being insects from a more contemporary age. 

In fact, the first geological evidence of the origin of insects is still uncertain; a few fragments of small arthropods have been found in some quartz from the Devonian period (prior to the Carboniferous, approx. 300 million years ago) and a group of scientists classified them as Thysanura, small wingless insects with a bare body and often covered in scales, lacking a marked metamorphosis. But, their true identity will be doubtful until more is known about them. The same can be said about three other fossils from the early Carboniferous period, consisting of some wings found in Czechoslovakia and Germany; the only thing that can be deduced is that, at that time, there existed flying insects with perfectly developed wings. 

From the following period (50 million years ago) the entomofauna is much better known; it is found to be already highly evolved and includes several groups with analogies to some current orders of insects. 

The insects of the Carboniferous period were gathered together by the the North American palaeontologist, Samuel Hubbard, into a large group which was named “Palaeodictyoptera” which have some similarities with the present orthoptera (cockroaches, locusts and crickets); these ancient insects were of medium size and as far as we know, all the representatives had a pair of membranous lobes on the first thoracic segment, thought to be indicators of the origin of functional wings. Unfortunately, their metamorphic stages are unknown. 

Other contemporaries of these giant dragonflies were those of the genus “Titanophasma”, with a long slender abdomen and narrow and membranous wings, almost as big as the former.  Metamorphic states have not been found in either of the two groups, but it is supposed that they were aquatic and of simple metamorphosis. As in that time, birds had still not appeared, nor any flying vertebrate, perhaps it was they who dominated the skies without being bothered by any other animal. 

Millions of years after the appearance of the first insects, during the Permian Period (215 million years ago) several types of chewing lice a few millimetres long, some sorts of bugs and Neuroptera were already found. Moreover, it is at this time that a strange order of insects appears similar to the present day beetle, with well developed wings but more slightly related to crickets, named “Protelytroptero”, important due to their complete metamorphosis. 

By the Mesozoic era, that of the gigantic reptiles, the entomofauna changed markedly and none of the extinct orders survived later than the beginning of this period. Among the insect representatives from this time are counted certain Australian species related to crickets which had a screeching apparatus on the wings; this is the first evidence of insects producing sound. 

As at this time, birds or other vertebrates that produce ordinary animal sounds had not yet appeared, it is possible that the screeching insects aforementioned and their relatives were the noisiest creatures of that time. From then on, insect fauna much resembles that of modern times, but more and more families continue to appear. In fact, the appearance of this fauna is so modern that, if we saw a collection of those specimens, stuck with a pin in the usual way, they would not seem so very different from our current collections, except that there would be no flower visitors, like bees and bumblebees, in as much as flowering plants only appeared in the following period, the Cretaceous (120 million years ago).

Although insects from the Tertiary period do not contribute to our knowledge of entomofauna’s evolution, as do the earlier periods, the do tell us about the geographic distribution of the families and the genera and they allow us to make definite comparisons against existing genera and species. To this age belong the very numerous fossil insects from Baltic Amber (till now, approx. 150,000 species have been collected), consisting of tiny crystalline sarcophagi in whose interior are found ancient insects in a perfect state of conservation. The material is in itself, the fossilized resin of an extinct pine (Pinitis succinifera), whose geographic distribution included extensive Nordic parts of Europe; many insects and other vertebrate that inhabited these forests became imprisoned in the resin of the trees they frequented.  Thenr, the resin crystallised, fell to the floor, became petrified and was then dragged by the waters to the beaches of the Baltic Sea where these incredible insect jewels can today be found. Dr.Morton Weler, who has dedicated himself to the study of Baltic Amber insects, has managed to differentiate between 43 genera of ants, of which, 24 exists nowadays. Moreover, he discovered that their social habits were as organized as existing ones with their castes, their workers and even in their association with greenfly.  As this occurred approximately 60 million years ago, before the time of the appearance of most mammal families in existence today, there is no doubt that the social organization of ants is very much older that ours.

Of all the primitive insects that we had till then, six different orders, all of them extinct for thousands of years apart from the group of the blattidae (cockroaches), insects have persisted over long geological periods, without noting any appreciable difference between the primitive species and the present.  Any small difference lies mainly in the arrangement of the veining of the wings and possibly in the size of the animal, since all the very abundant cockroach fossils that have been found are of relatively medium proportions and none of them surpasses in size to certain present species from our tropics.   

A detailed study of the origin of insects makes evident certain progressive structural changes over all the geological periods; although all this is still a controversial subject among the investigators, there is sufficient proof to indicate the important steps in these animals’ evolution. The morphological studies of present day insects prove that their first predecessors were apterous (wingless) like the present day Thysanura (Silverfish) that are occasionally found in libraries and shady places. The appearance of wings, probably a modification of lateral fins, was without a doubt, the most significant change in insect’s evolutionary line. 

Primitive flying insects could not flex their wings in a resting position. The second important evolutionary step consisted in the development of an articulation that permitted them to gather the wings on the abdomen when they were not flying; the attainment of this mechanism made them slippery and gave them the ability to hide themselves among stones, rocks and vegetative detritus. 

The third important evolutionary change consisted of achieving a more complete metamorphosis with larval and nymph stages. Since then, no changes of such importance have been produced. 

The insect fauna of our times is not more than a small part of the total which lived over the past 350 million years and have survived throughout this time without suffering such marked modifications as other living beings, but have adapted themselves marvellously to tolerate all varieties of conditions that there are upon the earth and it is expected that they have acquired specialities and adaptations that we do not fully understand. The degree of insect development is extremely variable and difficult to measure by human standards. It is well known by everyone that many species of ants, bees and termites with social tendencies, show a high degree of efficiency in their laborious constructions, moved by some inexplicable force defined as instinct, if it is not by faculties of reasoning and intelligence. 

There remains much to investigate about the phylogenetic evolution of insects. What is certain is that biology – helped with the discovery of carbon 14 – has made considerable chronological advances. The fossils of so many insects that lived in distant geological periods many millions of years before the human era are eloquent witnesses to the many vicissitudes which they overcame by means ill-suited to any other animal species. 

When thinking over and recognizing the chronological priority of insect in relation to us, that is to say, all that long time which passed before the appearance of man upon the earth of which they were witness, our childhood on the geological period table is, to Biologists’ eyes, in some way shameful.

Bibliography:

Notes about the origin of insects by Dr. Alvaro Jose Negrett. F.

INSECTS. Copyright 1963, United States-Department of Agriculture Washington D.C.

NATURAL HISTORY. Geology – (Palaeontology). Gallach Institute, Sixth Edition-Barcelona

EDUARDO HERNÁNDEZ PACHECO.  Fossils and fossilization.

THE INSECTS. Nature of Life Collection in Spanish -Offset Multicolour, SA 1968- México-D.F.  

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