Insect diversity Severely Underestimated: New Study Estimates 14 to 20 Million Species

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More than one million insect species have been scientifically described to date. That sounds like an enormous number, but it may represent only a small fraction of the true diversity. A new PNAS study concludes that at least 14 to 20 million insect species may exist worldwide. Previous estimates, by contrast, had put the figure at around six million species.

If the new estimate is correct, fewer than one in ten insect species would have been scientifically described. The knowledge gap is likely to be particularly large for small and easily overlooked insects, including many flies and parasitoid wasps.

How do you count species that no one knows about yet?

Since Carl Linnaeus introduced the system of scientific species names in the 18th century, taxonomists have described around two million species. But no one knows how many species actually live on Earth. Estimating the number of insect species is particularly difficult: They are enormously diverse, often tiny, and some live in habitats that are hard to access.

For their study, the researchers therefore had to find a different approach. They based their work on one of the world’s most intensively studied tropical habitats: the Área de Conservación Guanacaste (ACG) in northwestern Costa Rica. The protected area covers around 169,000 hectares and includes dry forest, rainforest, and cloud forest.

At 15 sites, the research team collected flying insects using Malaise traps. They gathered more than 1.6 million specimens. Using DNA barcodes, they were able to assign them to 53,945 genetically distinguishable units.

These units do not automatically correspond to 53,945 species that have already been scientifically described. The researchers used what are known as Barcode Index Numbers (BINs), which group animals according to the similarity of specific DNA segments and serve as proxies for individual species. Yet even this enormous sample captured only part of the insect diversity actually present in the study area.

Tiny wasps reveal how much remains hidden

The Microgastrinae, a highly diverse subfamily of braconid wasps, played a crucial role in the extrapolation. These parasitoid insects, usually only between one and four millimeters long, lay their eggs in lepidopteran caterpillars. Their larvae develop inside the host, which initially remains alive but eventually dies.

In the 15 core Malaise traps, the researchers found 388 Microgastrinae species or BINs. Far more comparative data were available for these wasps, however: In addition to specimens from extra traps, there were thousands of specimens that had been reared from previously collected caterpillars.

Across all sampling methods, 1,414 Microgastrinae units were known. But even with all these data, the actual diversity had not yet been fully captured. Using a statistical method that is also employed in epidemiology, the researchers compared the different datasets. The overlap between them can be used to estimate how many species were found by none of the methods.

They thus arrived at an estimate of 2,394 Microgastrinae species for the protected area. The 388 units from the 15 main traps therefore represented only around 16% of the estimated diversity of these wasps.

The research team then applied this ratio to all insects from the main traps. If these traps had likewise captured only around 16% of the existing diversity, the nearly 54,000 recorded species units would point to a total of about 333,000 insect species in the study area.

From one protected area to the entire planet

At this point, only the insect diversity in the protected area under study had been estimated. To infer the global number of insect species, Robert C. Colwell and his team used four other animal and plant groups for comparison: trees, mammals, amphibians, and saturniid moths.

For these groups, researchers know how many species occur in the Área de Conservación Guanacaste and approximately how many exist worldwide. This ratio can be used to estimate what proportion of global species diversity the protected area harbors. The researchers then applied these ratios to the previously estimated 333,000 insect species in the ACG.

Depending on the comparison group, this produced global estimates of around 14.2 to 20.3 million insect species. The average of the four calculations was around 17.3 million species. The researchers explicitly regard these figures as a conservative estimate—that is, a cautiously set lower bound. Ultimately, they believe that at least 14 to 20 million insect species may live on Earth.

This figure is not an exact inventory. It is based on two successive extrapolations: first, from the particularly well-studied Microgastrinae to the protected area’s entire insect diversity, and then from this area to the planet as a whole.

The most important finding is therefore not the precise figure within this range. What matters is the order of magnitude: The true diversity of insects could be two to three times greater than previously assumed.

Do more unknown insect species also mean more threatened species?

In the article for The Conversation, Dirk Steinke, one of the authors of the new study, points to a troubling consequence: If far more insect species live on Earth than we thought, the absolute number of species threatened with extinction could also be much higher.

One important caveat applies here: The PNAS study itself does not investigate how many insect species are threatened. It analyzes neither population trends nor the extinction risk of individual species. For now, its findings only change our understanding of the scale of global insect diversity.

This becomes relevant to species conservation when the new estimate is combined with previous assumptions about the proportion of species at risk. In its 2019 global report, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) estimated that there were around 8.1 million animal and plant species, about three-quarters of them insects. Since global threat assessments are unavailable for most species-rich insect groups, the report cautiously assumed that roughly 10% of insect species could be threatened with extinction. On this basis, IPBES arrived at a total of more than one million threatened animal and plant species.

However, if 14 to 20 million insect species do in fact exist, this order of magnitude would also change. Applying the 10% share assumed by IPBES to the new estimate would put the projected number at around 1.4 to 2 million threatened insect species.

This is not a new threat projection, but merely an extrapolation based on two estimates. Nevertheless, it shows that if actual insect diversity has been greatly underestimated, the absolute number of threatened species could be substantially higher than previously assumed.

There is another problem: For a large proportion of these presumed millions of species, there are no population data, no distribution maps, and no individual threat assessments. Many have not even been scientifically described. Species could therefore decline sharply or even become extinct without their disappearance ever being documented—or even noticed at all.

Unknown does not mean unimportant

The Microgastrinae show why our picture of the insect world remains so incomplete. Conspicuous butterflies, dragonflies, and large beetles are observed and studied relatively often. Yet much of the true diversity consists of smaller wasps, flies, and other insects that even experts can detect and distinguish from one another only with considerable effort.

Ecologically, these species are therefore far from insignificant. Parasitoid wasps influence the populations of their host species and are part of complex food webs. Other insects act as pollinators or decomposers, regulate other animal populations, or are themselves food for numerous species.

The current study thus also highlights a fundamental difficulty in tracking species extinction: We are trying to measure the loss of biodiversity even though we still do not know a large part of that diversity.

This does not mean that a species must be scientifically described before it can be protected. Particularly where knowledge of species is incomplete, the protection of entire habitats becomes more important. An intact peatland or a natural tropical forest protects not only known birds, mammals, and butterflies, but also numerous lesser-known or as yet undiscovered species.

What science has documented is only a fraction of the true diversity of insects. The study suggests that the part still unknown is considerably larger than previously thought.

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Sources

• Colwell, R. K., Guzman, L. M., Steinke, D., & Sharey, M. J. (2026): Constructing a lower-bound estimate of the global number of insect species on a hyperdiverse empirical foundation. Proceedings of the National Academy of Sciences 123(27), e2524283123. https://doi.org/10.1073/pnas.2524283123
• IPBES. (2019). Summary for policymakers of the global assessment report on biodiversity and ecosystem services. IPBES Secretariat, Bonn, Germany.
• Steinke, D. (August 9, 2026). New research estimates around 20 million insect species on Earth — doubling those facing extinction. The Conversation.
  https://theconversation.com/new-research-estimates-around-20-million-insect-species-on-earth-doubling-those-facing-extinction-288330