A recent paper published in the journal Science presents a reconstruction of the insect phylogeny (their ‘tree of life’ as it were) based on a gargantuan analysis of their DNA (1). The huge team (I counted 101 authors!) of researchers studied the genomes – and the amino acid sequences they code for – from insects and other arthropods in order to estimate the dates back in time, when the different orders of insects diverged (see figure below).
Insects have been around for a very long time. The oldest fossil insect found to date – a collembollan – comes from the Devonian Rhynie Chert in Scotland (c. 412 million years ago) (2). This recent molecular study however, suggests that insects (Hexapoda) may have evolved much earlier, in the Ordovician (c. 479 mya), or perhaps even earlier in the Cambrian period (541.0 – 485.4 mya).
What is particular interesting to me about this publication, is that it provides dates for the appearance of all of the orders of insects, as well as highlighting when some of the most significant events – such as the evolution of flight, and metamorphosis – occurred. For example, we learn that hemipterans (true bugs such as aphids, planthoppers, leafhoppers and so on) may have evolved in the Ordovician period (c. 373 mya), even though the oldest fossils found to date, are from much later, in the Carboniferous period (when coal deposits were formed in the UK).
Insects typically associated with the Carboniferous (c. 300 mya) are dragonflies: giant dragonflies with wings over two feet wide flew through the Carboniferous forests hunting whatever it was the fed on, probably other insects! In fact, winged insects probably evolved ever earlier than this: the study suggest that insect flight emerged in the Early Devonian (c. 406 mya) (1).
A large grouping of insect orders, including earwigs, stoneflies, grasshoppers, crickets, katydids, cockroaches, mantids, termites and the like, probably evolved in the Upper Carboniferous period (c. 302 mya). So this mantid (below), or others like him/her, have been around for a very long time!
Beetles, flies, wasps, ants, moths and butterflies are known to be ‘higher insects’ – so-called holometabolous insects which undergo metamorphosis – which have evolved more recently that some of their fellows. This study shows that the orders Hymenoptera, Diptera, and Lepidoptera underwent ‘spectacular diversifications’ in the Early Cretaceous at the same time that flowering plants were diversifying (or radiating) in terms of becoming the dominant flora on the planet (3).
So insects have been present on the earth for mind-boggling long periods of time, taking cataclysmic episodes – such major extinction events – in their strides, and going on to diversify into the multitude of types we see today. They have found ways of doing things, such as flying through the air, living together in cooperative societies and caring for off-spring, hundreds of millions of years before man, or even mammals, appeared on the scene. Many of them have evolved alongside flowering plants and their unique interactions with these plants – chemical, physical and biological – undoubtedly contributed to the development of such flora (including many that we rely on for food and medicine today). They are the great survivors and deserve our deepest respect.
1. B. Misof, S. Liu, K. Meusemann, R. S. Peters, A. Donath, C. Mayer, P. B. Frandsen, J. Ware, T. Flouri, R. G. Beutel, O. Niehuis, M. Petersen, F. Izquierdo-Carrasco, T. Wappler, J. Rust, A. J. Aberer, U. Aspock, H. Aspock, D. Bartel, A. Blanke, S. Berger, A. Bohm, T. R. Buckley, B. Calcott, J. Chen, F. Friedrich, M. Fukui, M. Fujita, C. Greve, P. Grobe, S. Gu, Y. Huang, L. S. Jermiin, A. Y. Kawahara, L. Krogmann, M. Kubiak, R. Lanfear, H. Letsch, Y. Li, Z. Li, J. Li, H. Lu, R. Machida, Y. Mashimo, P. Kapli, D. D. McKenna, G. Meng, Y. Nakagaki, J. L. Navarrete-Heredia, M. Ott, Y. Ou, G. Pass, L. Podsiadlowski, H. Pohl, B. M. von Reumont, K. Schutte, K. Sekiya, S. Shimizu, A. Slipinski, A. Stamatakis, W. Song, X. Su, N. U. Szucsich, M. Tan, X. Tan, M. Tang, J. Tang, G. Timelthaler, S. Tomizuka, M. Trautwein, X. Tong, T. Uchifune, M. G. Walzl, B. M. Wiegmann, J. Wilbrandt, B. Wipfler, T. K. F. Wong, Q. Wu, G. Wu, Y. Xie, S. Yang, Q. Yang, D. K. Yeates, K. Yoshizawa, Q. Zhang, R. Zhang, W. Zhang, Y. Zhang, J. Zhao, C. Zhou, L. Zhou, T. Ziesmann, S. Zou, Y. Li, X. Xu, Y. Zhang, H. Yang, J. Wang, J. Wang, K. M. Kjer, X. Zhou. (2014). Phylogenomics resolves the timing and pattern of insect evolution. Science. 346 (6210), 763.
2. MS Engel, DA Grimaldi (2004). New light shed on the oldest insect. Nature 427 (6975), 627-630.
3. Wing, Scott L., and Lisa D. Boucher. “ECOLOGICAL ASPECTS OF THE CRETACEOUS FLOWERING PLANT RADIATION 1.” Annual Review of Earth and Planetary Sciences 26.1 (1998): 379-421.