The brilliant mathematician and biologist JBS Haldane is famously quoted as once having said, “God had an inordinate fondness for beetles”. He was referring to the fact that nearly half of all insect species known are beetles, but over 50 years after his death, scientists are still gaining new insights into their amazing success. A new study reconstructing the beetle family tree suggests that it is the versatility of beetles that has allowed them to survive even the most testing of times.

There are over 400,000 described species of beetle. That is, the ones scientists know about. They make up 40% of all the insects we know about (and insects may represent 90% of all animal species!!). Most academics agree there are probably at least another million species of beetle we’ve never formally recorded, although it could be as many as 100 million! Why are there so many beetles on Earth?

A recent paper published in the journal Systematic Ecology reconstructed the beetle family tree using genetic data from over 360 different species. It outlined how beetles flourished and diversified over the last 300 million years, and suggested that their hard wing cases, which enable them to live in closed environments such as leaf litter and soil, were crucial in enabling them to diversify into millions of species, and for those species to avoid extinction.

Reconstructing key dates within the evolutionary history of beetles, the authors showed that beetles diversified rapidly within the Cretaceous period (145 – 66 million years ago). This was a period when plants were also undergoing rapid evolutionary change, and the authors note that many of the most successful groups of beetles are those that feed on plant matter. The ability to adapt to diets of living plant matter as well as dead material such as leaf litter and soil may have been key to the enormous diversity of beetles we see today.

This idea was further explored in a second paper by the same author, which looked at the evolutionary transitions in one group of beetles. The paper concluded that leaf litter has been a key intermediate step in beetle evolution, allowing species to transition between different lifestyles ranging from aquatic predators to decomposers and herbivores. Together, these studies suggest that hard wing cases opened up leaf litter and other close habitats to beetles, which in turn allowed them to reach many other niches. Adaptability is a great defence against extinction, and it seems that shielding their wings gave beetles unprecedented adaptability through no less than three mass extinctions. Hopefully they’ll survive a fourth.

Want to Know More?

• McKenna et al (2015) The beetle tree of life reveals that Coleoptera survived end-Permian mass extinction to diversify during the Cretaceous terrestrial revolution Systematic Ecology
• McKenna et al (2015) Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles Systematic Ecology