Clint Penick: Illustrating insect diversity

Photo Credit: Flickr

Winter 2017 | Greer Arthur

Counting all the insects in the world is no easy task. As one of nature’s great success stories, not only are insects found absolutely everywhere, their numbers are gargantuan. Insects make up nearly half of all existing species and account for the largest portion of life on Earth. To date, over 1,000,000 insect species have been described—a staggering triumph over mammalian species, which number at a mere 5,898. To depict this remarkable diversity, my colleague Magda Sorger and I unveiled our update to the SPECIES SCAPE—a famous diagram of global biodiversity—at this year’s International Conference of Entomology (ICE) in Orlando, Florida. Since insects comprise such an enormous proportion of life on this planet, our work on SPECIES SCAPE will hopefully serve as a poignant reminder that insects play a critical part in all environments and must therefore be protected.

Our SPECIES SCAPE is not the first. The project began when Quentin Wheeler, an entomologist, taxonomist and the current president of the State University of New York College of Environmental Science and Forestry, worked with Frances Fawcett, a scientific illustrator, to publish an illustration in The Annals of the Entomological Society of America in 1990. The illustration depicted trends in biodiversity and provided a direct comparison between multiple groups. In the original and our update, different groups of species are represented by a chosen creature— in our diagram an elk represents all mammal species, while a fly represents all insect species. To provide perspective, the size of each creature is scaled according to the number of species within each group. For instance, the monstrous fly in our SPECIES SCAPE, which swamps almost a quarter of the page, conveys the fact that the number of insect species vastly outweighs the number of species in any other group. This contrasts with the animals people tend to think of most—birds, reptiles, fish, and mammals—which are represented by some of the smallest pictures in our SPECIES SCAPE.

In contrast to the original, our updated illustration contains several modifications. First, we considered several significant changes to taxonomy. For instance, since Wheeler and Fawcett’s publication, “algae,” a diverse group of aquatic organisms capable of photosynthesis, now no longer exists as a formal classification. Instead, algae have been divided into multiple and sometimes- unrelated groups. The largest of these groups is Chromista, which means “colored”— a reference to their characteristic brown-gold pigmentation—and was used to replace algae in our illustration. Second, we decided to totally exclude certain groups of organisms that were included in the original diagram such as bacteria. Decisions such as this were made because the number of bacterial species is greatly debated and likely far more diverse than current numbers suggest. This is probably true for other classes as well, such as fungi, although we did include fungin our update. Third, we limited ourselves to 17 major groups by setting a minimum threshold of 5,000 species per group. Although most species fell into groups that met this threshold, some of our favorite groups didn’t make the cut, like the 1,167 species of tardigrades, water-dwelling micro-animals that resemble microscopic bears.

After setting exclusion criteria, we also made decisions regarding the inclusion of different taxonomic levels. In our update we included the kingdoms of plants and fungi, but we split the animal kingdom into separate phyla and smaller groups like birds and fish. During this process we discovered that even some of these well-known groups were not as clear as previously thought. The word “fish” is actually a collective name for several distinct lineages, and their former class, Pisces, is no longer used informal classification. Even crocodiles, it turns out, are more closely related to birds than to other reptiles, leaving some scientists to consider whether birds and reptiles should belong to a single group. However, we chose to maintain these common divisions since they are what most people commonly recognize. To emphasize the diversity of insects, we split them off from all other non-insect arthropods (invertebrate animals with a segmented body, an exoskeleton and jointed limbs) such as crabs and spiders. While insects were the clear winners in terms of extensive diversity, the remaining arthropod group still held a place just behind plants as the third most diverse group with over 200,000 species.

Despite intense study, current estimates suggest we have only cataloged 10 to 20% of all species, and even these estimations are generous. The discovery of new species endures today and is set to continue into the distant future. Consequently, our update of the SPECIES SCAPE is really a work in progress—a snapshot in time of the number of known species that will soon change again.

What is unlikely to change, however, is the dominance of insects. In 2009, only 41 new mammal species were described, a stark comparison to the 13,000 new species of arthropods that were reported, the majority of which were insects. We hope our update of the SPECIES SCAPE encourages more people to consider the role of insects in our world as well as our need to protect their diversity. Right now, there are nearly 12,000 species listed on the IUCN Red List of Threatened Species as “endangered” or “critically endangered,” but only 4% of these are insects. Compared with larger, more charismatic animals, insects typically receive less attention from a conservation perspective, but their diversity suggests they are equally or perhaps even more important than other animal groups. Projects like SPECIES SCAPE can help raise awareness about how diverse insects really are and why they deserve our protection.