In the heart of the Amazon, a scientist and his fogging machine revealed a hidden universe of millions of unknown species.
Imagine standing in a vast tropical rainforest, your gaze fixed on the green canopy dozens of meters above. To most, this is simply the roof of the forest. But to Terry Erwin, it was an unexplored frontier—a living library containing millions of unknown stories. An entomologist and curator at the Smithsonian's National Museum of Natural History, Erwin dedicated his life to documenting the smallest inhabitants of our planet: beetles 1 6 .
"If you are out in the rainforest, every single day, actually maybe every hour, there's a tremendous discovery. And that's what's really rewarding—discovery."
His work would fundamentally change how scientists measure Earth's biodiversity, sparking a global conversation about the number of species we share the planet with and the urgency of documenting them before they disappear. Through his pioneering exploration of the forest canopy, Erwin revealed that our planet was far more diverse than anyone had imagined, setting off a race to understand and conserve life's richness in the face of rapid environmental change 2 .
Growing up in Vallejo, California, Erwin developed an early appreciation for nature through childhood summers spent camping and fishing in the Giant Sequoia forests with his family 2 . He discovered Henry W. Bates' "The Naturalist on the River Amazons," which became a guiding inspiration for his future expeditions 2 .
Under the mentorship of Professor J. Gordon Edwards at San Jose State College, Erwin earned both his B.Sc. (1964) and M.A. (1966) degrees, focusing his master's thesis on bombardier beetles 2 . He then pursued his Ph.D. at the University of Alberta under Professor George E. Ball 2 .
After completing his doctorate, Erwin's career took him to prestigious institutions: a post-doctoral fellowship at Harvard University's Museum of Comparative Zoology, followed by study with Professor Carl H. Lindroth at Lund University in Sweden 2 .
By the time he began his position as Associate Curator of Coleoptera at the Smithsonian Institution in 1970, Erwin had studied with some of the most prominent carabidologists of his era 2 .
Henry W. Bates' "The Naturalist on the River Amazons" inspired Erwin's future expeditions.
Studied under prominent carabidologists including George E. Ball and Philip J. Darlington.
Early research focused on bombardier beetles and their defensive chemical spray.
Began as Associate Curator of Coleoptera at the Smithsonian Institution in 1970.
Before Erwin's pioneering work, the forest canopy was largely an unexplored frontier—difficult to access and poorly understood. Scientists knew this aerial realm hosted diverse life, but had no way to systematically document its inhabitants. Erwin changed this in 1975 when he adapted the "fogging technique" to explore the canopy, turning it into a rich source of data rather than an inaccessible mystery 2 .
His approach was both simple and revolutionary. Erwin used a biodegradable insecticide to create a fog that would temporarily stun the arthropods living in the canopy of a single tree, causing them to fall onto collection sheets spread on the ground below 2 . This method allowed him to capture thousands of specimens that represented hundreds of species, many previously unknown to science.
The data Erwin collected through fogging would lead to one of the most provocative and influential estimates in modern biology. In 1982, he published a paper examining canopy beetles and their host plant relationships to understand how many species might exist in just one acre of Panamanian forest 6 .
His reasoning followed a logical, if startling, chain of calculations:
Ironically, as Erwin himself noted, the famous "30 million species" figure appeared almost as an afterthought in the last paragraph of his groundbreaking paper—a "throwaway" line that would nonetheless ignite a global debate about planetary biodiversity 6 .
| Step | Finding | Significance |
|---|---|---|
| Canopy Sampling | Thousands of unknown arthropod species in a single tree type | Revealed unprecedented, hidden diversity in forest canopies |
| Beetle Proportion | Beetles comprised ~40% of arthropod samples | Provided a manageable taxonomic group for extrapolation |
| Host Specificity | ~20% of beetle species were host-specific | Suggested high beta diversity (species change between habitats) |
| Global Extrapolation | Projection across all tropical tree species | Estimated 30 million arthropod species total |
The estimate sparked controversy and debate throughout the scientific community. Some researchers questioned Erwin's assumptions, particularly about the degree of host specificity among tropical insects. Over time, the figure has been debated, refuted, and revised downward—current approximations suggest approximately seven million arthropod species 6 . Nevertheless, Erwin's central insight—that planetary biodiversity was vastly underestimated—forever changed the field.
Erwin's revolutionary work required both innovative techniques and specialized equipment. His toolkit combined entomological standards with creative adaptations for accessing the previously unreachable canopy environment.
| Tool/Technique | Function | Significance |
|---|---|---|
| Canopy Fogging | Releasing biodegradable insecticide into the canopy to stun arthropods | Enabled systematic collection of canopy insects; revolutionized canopy studies |
| Collection Sheets | Large sheets placed on ground to catch falling specimens | Allowed for quantitative sampling of canopy diversity |
| Aspirator | Handheld device for collecting individual insects | Used during nighttime Carabidae hunts in the forest understory |
| Flight Intercept Traps | Traps to capture flying insects | Documented additional diversity beyond fogging samples |
| Taxonomic Expertise | Deep knowledge of carabid beetle identification and classification | Enabled interpretation of collected specimens and discovery of new species |
Erwin's approach to fieldwork was holistic and relentless. Colleagues recall him rising at 4 a.m. to set up canopy fogging operations, working "as if the rainforest were his orchestra and he the conductor" 6 . Even after long days, he would venture out with head torch and aspirator to hunt for carabid beetles, demonstrating an unwavering passion for discovery 6 .
Terry Erwin's influence extends far beyond his provocative species estimate. During his more than 50-year career, he made substantial contributions to taxonomy, conservation biology, and mentoring future scientists.
Erwin was a prolific systematist who described 439 species of Carabidae (ground beetles), along with 22 genera and 4 tribes 6 . His meticulous work established a foundation for understanding beetle evolution and relationships.
Later in his career, he embraced new technologies like DNA barcoding, collaborating with the International Barcode of Life Consortium to incorporate genetic data into biodiversity documentation 6 .
Erwin's work came at a critical time—the 1980s and 1990s, when concepts like "biological diversity," "megadiverse countries," and "biodiversity loss" were entering scientific and public consciousness 2 .
His dramatic findings provided tangible evidence of how much we had to lose through deforestation and habitat destruction. By revealing the incredible diversity hidden in tropical forests, Erwin's work strengthened the case for conservation and inspired greater public awareness about protecting these vulnerable ecosystems 2 .
Perhaps less visible but equally important was Erwin's role as a mentor. Colleagues remember his "greatest spirit of academic generosity," always willing to share advice, specimens, or references from his encyclopedic library 6 .
He understood the importance of nurturing new talent, particularly supporting women scientists and researchers from developing countries 6 .
"Standing on the shoulders of giants allows us to see farther."
Terry Erwin passed away in 2020 at age 79, but his race to document biodiversity continues through the many scientists he inspired 6 . His work transformed our understanding of life on Earth, revealing a planet far more diverse than we had imagined. More importantly, he provided both the methods and the motivation to explore this unknown diversity.
The "rain of thousands of unknown arthropod species" that Erwin brought down from the canopy 2 represents both a scientific opportunity and an urgent responsibility. In an era of rapid environmental change, his legacy reminds us that we cannot protect what we do not know exists. The challenge he identified—documenting and conserving Earth's biodiversity—remains one of the most pressing in modern science.
As Erwin himself recognized, standing on the shoulders of giants allows us to see farther 2 . Through his work, he became one of those giants, offering his shoulders to a new generation of scientists racing to understand our planet's incredible diversity before it disappears.