‘Insects outnumber all species on Earth — some beetle groups are as old as dinosaurs’

Brian D. Farrell teaches evolutionary biology at Harvard University. Speaking to Srijana Mitra Das at
Times Evoke, he discusses how insects evolved over 300 million years and why these are ‘Earth’s primary engineers’:
What is the core of your research?

I study the role of ecological interactions in producing diversity in species — I research if the differences in how species manage in the world produces their diversity or whether it is the reverse. I thus study the intersections between ecology and long-term evolution.


Why is insect biodiversity important?
Insects pollinate plants — they are responsible for the food of the world. Insects also recycle perished material.
I term insects the principle denizens of Earth because of their key functions and how they are the essential intermediaries between plants and all the vertebrates that depend on these. You could take away all the birds and mammals but Earth would still have productive crops as long as there are insects — they are the primary engineers of our planet.

Insects also outnumber all other species on Earth — of the million and a half known organisms on the planet, over
a million are insects. They weigh as much as all the other species put together — they are the majority of Earth’s biomass.

What are some of your findings on beetles and their evolution?Beetles are the largest group of all insects — about one of every four animals is a beetle as are around 30% of all insects. These include parasites, pollinators, plant consumers, insect-eaters, etc. I study the age of interactions or how long species are associated with each other and how that history is reflected in the interactions we see today — if you were to walk into a forest or a field, could you understand who eats what, which insects proliferate which plants, etc., by studying their current ecology, like how large they are? The answer is no — to understand these ecosystems, you need to understand how old these beings are.

CAPTURED IN AMBER: The palm beetle Delocrania sp, preserved in amber here, is about 15 million years old — found in the Dominican Republic, while the Delocrania went extinct there, it looks identical to certain beetle species found in Central and South America today. Photo Courtesy: B. Farrell

In my research, I discovered relate insects feed on related kinds of plants. I call such insects, which are much smaller than the things they eat, ‘tiny consumers’, from beetles to caterpillars, worms to viruses. It turns out they all evolved in similar ways — and they are very slow to change what they eat. One kind of beetle I’ve worked on feeds only on milkweed. You won’t find a mango beetle suddenly consuming pine trees or potato beetles abruptly eating grasses. Certain insects tend to be very conservative in their evolution of new associations.

Now, about twenty years ago, I was working on a group of beetles which feed on pine trees or cycads, which, at 300 million years in age, are among the oldest plants on Earth. I sequenced their DNA and compared their evolutionary history to the plants they eat. I found the beetles that feed on the oldest plants which were around when the dinosaurs were here — pine trees, conifers, cycads — are as old as the plants themselves. They’ve been feeding on them for two to three hundred million years. So, these insects are like little dinosaurs themselves. This research came out around the same time as Steven Spielberg’s ‘Jurassic Park’ movies and the New York Times presented a two-page spread on this, highlighting how ancient these ecological associations actually are.

I also found how the beetles which made the rare change, from feeding on ancient plants to younger ones, became much more diverse — they produced the majority of species on Earth. So, ecological associations can be very old and conservative but shifts can dramatically alter ecology. Long-term evolutionary history has a profound relationship with ecological interactions we see today.

Working in South American forests, what are some interesting insects you’ve seen?

I’ve seen fireflies which light up an entire forest at night. There are iridescent Morpho butterflies with blue reflective wings that are bright enough to be seen from space. I’ve seen five-inch-long plant-eating beetles which consume giant rain forest trees and cicadas which build chimneys of clay upto a foot tall to get them air underground when the floods come.

A WISE LITTLE MONARCH: The caterpillar of the Monarch butterfly (Danaus plexippus), found in the USA, has a closely related Indian species, the Common Tiger butterfly — both feed on milkweeds with poisonous latex in their leaves, but the larvae is able to cut the leaf’s central vein to drain out the latex, then eating the leaf tips, as shown here. Photo Courtesy: B. Farrell


Have insects evolved special ways of communication as well?In nature, the only thing more important than getting enough to eat is finding a mate — for this, animals compete through singing. Interestingly, when a cicada starts singing, all the other species stop because they simply cannot compete with this loud little being. When singing, the tiny cicada dominates the forest — and, through the march of time, every other species has learnt to wait for its turn.

Are human actions now impacting this extraordinary and ancient world?
There is sizable research on ‘insect armageddon’ or the disappearance of insects from Earth. Data shows a fraction of insects are around now compared to the numbers forty years ago. This is deeply worrying — if insects were to disappear, we wouldn’t know what to do or how to bring them back. Some research highlights neonicotinoide insecticides as causing such damage while others point to light pollution. Insects which have evolved over millions of years are now the first indicator of how much our environment is suffering from human impacts.

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