Like it or not, we are surrounded by bugs. It has been estimated that for every person alive today, there are some 200 million insects. They are the most diverse group of living animals, with around a million different species known to science.

Why are insects so numerous? What is the secret to their success? Scott Richard Shaw tackles this long-standing question in Planet of the Bugs: Evolution and the Rise of Insects. As an entomologist with more than three decades of experience who has personally discovered some 163 new species of insects, Shaw is a masterful guide to their intimidating diversity and complicated history.

He begins by emphasizing the variety and ubiquity of his favorite organisms, as well as impressing the reader with some memorable entomo-facts: “Dehydrated fly larvae [of the South African species Polypedilum vanderplanki] can tolerate immersion in boiling water as well as being dipped into liquid helium.”

The majority of the book traces the origin and diversification of arthropods — the greater taxonomic group containing insects, crabs, spiders, centipedes, and others with more than six legs. Each chapter examines a different geological time period and describes the physical conditions and changes happening then on earth, while also introducing the major groups of insects that first appear in the fossil record during that time.

For some, the emphasis on the details of deep history may be cumbersome, but Shaw’s command of geology is impressive, and he makes an effort to tie the origins of particular structures and behaviors of arthropods to the changes taking place around them, and vice versa.

He is careful to point out that our understanding of insect evolution is limited by the scattered nature of the fossil record, which he compares to a family photo album: “Maybe when you were born your parents bought a camera and took lots of pictures, but over the years they took photographs sporadically, and sometimes they got busy and forgot to take pictures at all.”

One of the more intriguing ideas Shaw puts forth is that the earth’s supply of fossil fuels — essentially, the remains of early plants — might be primarily restricted to layers from the Carboniferous period because that is when plants originated, and few organisms were yet capable of eating them. Soon, insects — especially termites — evolved the ability to digest cellulose, and plants that died were quickly consumed before they could be fossilized.

This suggests that fossil fuels are limited today not simply because they take a long time to form, but because there was only a small window of time in which early plants were sufficiently common but effectively inedible. The upshot is that the process ended long ago, so we cannot simply wait around for more petroleum to form.

Shaw is at his best when describing the group in which he specializes: the parasitic wasps. His discussion of the evolution of wasp venom — originating as a fluid that lubricated the lining of egg-laying ducts and later developing into a substance that could paralyze a victim to make it food for growing larvae — is intriguing. He is particularly effective at dispelling misconceptions, pointing out that, despite what exterminators might suggest, most insects are not pests.

Shaw repeatedly points out our inherent bias toward vertebrates, but then, in turn, seems to subscribe to an arthropod-centric outlook. For example, “In my opinion, the origins of human tool use, fine motor skills, manual dexterity, and ultimately the rise of human civilization are firmly rooted in our ancestral insectivorous diets. We may owe our very existence to social cockroaches. If termites weren’t abundant, would primates ever have come back down out of the trees? I doubt it.”

In some cases, this bias clouds his view of evolutionary milestones, like when he suggests that wood wasps were the first organisms to invent parasitism, despite the fact that the adoption of parasitic lifestyles by microbes like bacteria, protozoans, and fungi certainly predated that of the insects by many millions of years.

Shaw also goes a bit far when he suggests in the postscript that the incredible success of arthropods on earth implies that their evolution was inevitable — not just on earth, but on other planets, too. He calls this idea the “buggy universe hypothesis,” which, he points out, “is contrary to much of what I was taught,” yet argues that it should be considered a valid hypothesis.

Perhaps, but as Shaw himself says, we have a lot to learn about the insects here on earth before we start considering those that might possibly live in faraway galaxies. Indeed, some estimates suggest that as many as 80 percent of insect species on earth remain unknown to science.

Just why have insects become so numerous? Shaw identifies three primary reasons: small size, the ability to fly, and the complex development that some insects undergo in which adults differ substantially from their young (think butterflies and caterpillars), allowing them to occupy different ecological niches and thereby avoid competing with one another. These are not new ideas, but they are presented clearly, and Shaw explains how each has contributed to the success of particular groups.

Hardcore entomologists may cringe at his casual language — like his use of the term “bug” to refer to any insect, which is technically reserved for just one subgroup, the Hemiptera. On the other hand, science-minded readers will appreciate how alternative, competing hypotheses are presented for various unresolved questions, like why insects first evolved flight and the causes of mass extinctions.

In the end, Planet of the Bugs succeeds as an accessible introduction to the evolutionary history of the organisms that truly dominate our planet. (Hint: It’s not us.)

Scott Solomon teaches ecology, evolutionary biology, and scientific communication at Rice University. His research has explored the diversity and evolutionary history of ants and their symbiotic partners. He has written popular articles on topics ranging from how fossils are used in the study of human evolution to how slime molds engage in agriculture. His first book, Future Humans: The Ongoing Evolution of Homo Sapiens, will be published by Yale University Press in 2016.

 

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