The world’s first insect

Author: Julián Monge Nájera, Ecologist and Photographer 

If we could visit the earth more than 400 million years ago, to see the first insect, ancestor of all the millions of species of insects that live today, what would it be like? How did that first insect behave? What did it eat and who were its enemies? Incredible as it may seem, we can answer all this and even more: DNA analysis indicates that today there is an animal that profoundly resembles that first insect, and you can see it with your own eyes!

Devonian microlandscape: the earth 400 million years ago. Painting: Deposits Online.

At the beginning of the Devonian period, when terrestrial ecosystems were still young and very different from today; and the continents were unrecognizable to us, the female of a tiny animal underwent an inheritable mutation that made her the ancestor of all insects that currently populate Planet Earth, by millions of species and billions of individuals.

Since I was a student I was fascinated by the mysterious origin of these animals: what would those first insects look like? Could they fly? I read everything that fell into my hands, especially a very nice article by Dr. Jarmila Kukalova-Peck¹; I wrote to her asking for more information and she treated me with the greatest kindness and sent other papers and a letter explaining her work; I was so excited with the subject that I even built a model of the «ancient insect» using pieces of wood and cardboard.

Years passed, I moved on to other things, and recently, I don’t remember why I asked myself what had happened in these three and a half decades. How far has science advanced on this question since the days when we did not analyze DNA and could only look at a few fossils available and come up with ingenious ideas?

Fortunately, Michael S. Engel reviewed the subject a few years ago and made my job easier². Generally, DNA studies agree with the conclusions that previous scientists have made using only animal anatomy.

The first insects were tiny animals, a few millimeters long, that lived in the soil, probably in cracks in the ground and under decomposed vegetation, on which they fed, along with fungi, spores, and, perhaps, bacteria and protozoa.

In the head, they had external jaws, eyes, and some type of sensor (predecessor of today’s complex antennae); a thorax with three pairs of legs; and an abdomen with some type of structures at the end (sensory or for mating).

The life of the first insects began with the male demonstrating his strength to the female in some way, in some kind of “dance”, and if she accepted it, he deposited on the ground a drop or structure with his sperm, which she collected to fertilize her eggs. There was no metamorphosis, instead of a larva, what emerged from the egg was a tiny version of the adult, which just grew with each molt. And they could they fly: the first insects lacked wings. Their enemies must have included parasites such as viruses, bacteria, protozoa, fungi, and nematodes, which to date continue to parasitize insects. Their predators were probably spiders and scorpions; little else was living on land at the time.

400 million years ago a spectacular mutation had already taken place: from lateral elongations that perhaps allowed the insect to warm up or glide, mobile wings arose, surely using the same genes that are responsible for moving the legs of insects. This, of course, happened somehow, but we still have no evidence of how exactly it happened.

The next big advances were: being able to fold the wings to protect them; the appearance of larvae that did not compete with adults for the same food; and, in the time of the dinosaurs, the formation of societies like those of ants, termites, and bees; as well as a fruitful relationship with flowers that lasts to this day (pollination).

We already know what the first insects were like, now let’s see who their closest relatives are today, and why I say not only that they look alike, but that we can see them with our own eyes.

This is the closest thing to an ancient insect, the silverfish: 

Silverfish, Zygentoma, Photography: Fritz Geller-Grimm.

If you are thinking that the silverfish does not look like a butterfly, fly, or whatever comes to your mind when you think of an insect, you are right. But if we compare it with the nymph of a primitive insect, the Mayfly, the resemblance is striking:

Mayfly nymph, a primitive insect whose adult lives for a few days. Photography: Amada44.

We can see silverfish with our own eyes because they are found in many houses, where they eat every starchy product they find, as well as paper and cardboard, which is why they are particularly feared in libraries. Unlike insects, which evolutionarily explored all kinds of bodies and lifestyles, the silverfish is the conservative relative, which lives today almost as its predecessors lived 400 million years ago, opening a wonderful window to the Devonian, the cradle of land life.

*Edited by Zaidett Barrientos, Katherine Bonilla y Carolina Seas.

Originally published  in Blog Biología Tropical: 11 September 2020

REFERENCES

¹ Kukalova‐Peck, J. (1978). Origin and evolution of insect wings and their relation to metamorphosis, as documented by the fossil record. Journal of Morphology, 156(1), 53-125.

² Engel, M. S. (2015). Insect evolution. Current Biology, 25(19), R868-R872.