The Earth is truly a planet of insects. There are “billions of billions” of ants crawling around, and there could be up to 2,400 species of fireflies alone. While those numbers may seem like a lot, a new study estimates that up to 20 million insect species live on Earth, instead of the six million previously believed. Only a fraction of these species have been discovered, according to a study published today in the journal Proceedings of the National Academy of Sciences (PNAS).

Insects are diverse for several reasons. Many species undergo metamorphosis during their life cycles, meaning they can live in different habitats depending on their life stages. For example, caterpillars eat plants at a younger age, but when they become butterflies or moths, they feed primarily on flower nectar. Additionally, since insects are mostly small, they can maintain populations in more hidden and restricted areas that are harder for scientists to access.

The estimate that the planet is home to around six million species of insects has been around for 40 years. Since it’s so difficult to sample these tiny organisms that are really good at hiding, getting an accurate count of insect species is a Herculean task.

“The central problem is that most insects are rare, and even with huge samples new species continue to be found,” says Robert Colwell, co-author of the study and an entomologist at the University of Colorado Museum of Natural History and the University of Connecticut. popular science. “We collected more than 1.6 million individuals in traps that were in operation for 69 years in Costa Rica and we still had not captured everything that lived there. The statistical challenge is to estimate not only what you have seen, but how much you are missing.”

To address this problem, Colwell, University of Kentucky professor emeritus Michael Sharkey, and Cornell University entomologist and biodiversity scientist Laura Melissa Guzmán took an in-depth look at a well-studied subgroup of parasitic wasps called Microgastrinae. These wasps lay their eggs inside caterpillars. When the eggs hatch, the larvae eat the inside of the caterpillar, grow and eventually emerge. The team studied wasps found in the Guanacaste Conservation Area (ACG) in northwestern Costa Rica.

They used the flying insects as a “measuring stick” to determine how incomplete their larger sample was. Two of the team’s sampling methods used tent-type traps called Malaise traps, including a central set of traps and a peripheral set, and the third set collected caterpillars and analyzed the wasp species that emerged from them.

The team used several statistical models to determine a ratio between the number of these wasps compared to the number that live undetected. They found that there may be between eight and 14 million additional species.

“It is almost certain that most are small, rare and highly specialized,” Guzmán says. popular science.

According to Guzmán, 75 percent of the parasitic wasp species the team found were captured by just one of our three sampling protocols, even within the same forest. This indicates that these species have niches or behaviors that are specific and narrow enough that a single type of trap can miss them.

“Many will probably turn out to be parasitoids, insects that complete their life cycle inside other insects, meaning they are embedded in food webs that we don’t yet understand,” he explains. “Some may only exist in the forest canopy, which we barely sampled.”

Doubling or tripling the estimated insect species, which already constitute the most diverse group of animals, could have profound implications for understanding the scale, richness and future of our planet’s biodiversity. Human activities are driving global insect extinction, and a new estimate could help protect those that remain.

“We cannot protect species if we do not know they exist, therefore, in order to understand the biodiversity of our planet, it is important to know how many there are,” added Guzmán.

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