A new estimate of insect species globally finds that there may be 8 to 14 million more species than people thought, with few of them discovered yet.

Most experts have currently accepted an estimate of about 6 million insect species, an appraisal that has stood for the last 40 years. But the new count, which used genetic information for 1.6 million individual tropical insects, a census of a highly diverse group of parasitic wasps in Costa Rica, and statistical strategies, conservatively estimates the total number of insect species at closer to 14 to 20 million.

A group of researchers from Cornell University, the University of Kentucky, the University of Colorado, and the University of Connecticut published a study in the Proceedings of the National Academy of Sciences, that claims a doubling or tripling of estimated insect species – already established as the most diverse group of animals – has profound implications for understanding the scale, richness and future of biodiversity on Earth.

“We cannot protect species if we don’t know that they exist, and so to be able to understand the biodiversity on our planet, it’s important to know how many there are,” says Laura Melissa Guzman, Cornell assistant professor and the paper’s corresponding author.

Scientists have described – meaning they have named and characterized insects so others can identify them – only about 1.2 million insect species so far.

“We know there are many more to go, and one of the challenges is that the more we sample, the more we discover,” Guzman says. “It’s a question of trying to estimate what is unobserved based on what we know.”

Insects are so diverse for a few reasons: Many undergo metamorphoses during their life cycles, which allows them to exploit different habitats based on their life stages. For example, caterpillars feed on plants earlier in life, and then when they become butterflies or moths, they feed primarily on flower nectar. Also, insects are mostly small, enabling them to maintain populations in very restricted areas.

In the study, the team of researchers, led by UConn Department of Ecology and Evolutionary Biology Distinguished Professor Emeritus Robert Colwell, Guzman, and University of Kentucky Professor Emeritus Michael Sharkey, took advantage of intense insect sampling at the Área de Conservación Guanacaste (ACG) protected area, encompassing 169,000 hectares (417,600 acres) in northwestern Costa Rica. They first used three methods to conduct a deep sample of Microgastinae – an extremely diverse subfamily of small parasitic wasps – in the ACG. The wasps lay their eggs inside caterpillars, and when hatched, the larvae consume the insides of the caterpillar, grow, and eventually emerge.

Two of the sampling methods involved tent-like traps called Malaise traps, including a core set of traps and a peripheral set, and the third involved collecting caterpillars and analyzing the wasp species that emerged from them. Combined, the three sample sets yielded nearly 22,000 specimens representing 1,414 Microgastrinae wasp species, based on DNA barcodes – a technique where a small segment of DNA is sequenced to determine unique species. The team used a statistical method from epidemiology, developed by co-author Anne Chao, to combine the three datasets and estimate the total number of Microgastrinae species in ACG (2,394), including species present, but undetected in the samples.

The fifteen core Malaise traps captured more than 1.6 million insect specimens — of all kinds — yielding nearly 54,000 insect species based on DNA barcodes. Of these, 388 species were Microgastrinae. To estimate the total number of insects species in the ACG, the team first calculated the ratio of core Microgastinae to the estimated total for ACG (388/2394). This ratio was then applied to the 54,000 insect species captured by the core Malaise traps to estimate true species count of all insects in the ACG, which equaled close to 333,000.

To estimate how many insect species there might be on Earth, they determined the ratio of estimated global tree species (around 73,000) compared to the estimated number of ACG tree species (1,200-1,500). By applying that tree ratio to the estimated 333,000 insect species in ACG, the research team ultimately estimated a range of total insect species globally of 14 million to 20 million.

Recent reports have warned of human activities leading to a dramatic die-off of global insects, dubbed the “insect apocalypse.” The new global insect estimate may be a step toward knowing and protecting those that remain.

“Our results point to a large number of undescribed insects, those without a name,” says Guzman. “With recent reports of insect declines, there could be many species that are declining that we haven’t even discovered.”

Colwell notes, “The diversity of tiny, undescribed insects (especially micro-wasps and miniscule flies) — not only in the tropics but everywhere — vastly overwhelms the number of well-known, larger insects familiar to the public.”

Of the 15 study co-authors, Colwell, Sharkey, and Guzman contributed equally to the work. The study was supported by Canada’s New Frontiers in Research Fund, the Canada Foundation for Innovation’s Major Science Infrastructure program, the Walder Foundation of Chicago, the University of Southern California and Cornell University.