Scientists Thought California Had as Few as 26,000 Insect Species. They Were Way Off

Insects are the most diverse group of animals on Earth. Scientists have described about one million species, but they believe this only accounts for a fraction of those that exist. Even counting the number of species in a single state presents a huge challenge, as a new study on California’s insect diversity clearly illustrates. Prior to this research, surveys led by the University of California collectively described about 12% of California’s insect diversity, leading scientists to estimate that there are between 26,000 and 100,000 species in the Golden State. The results of a new survey, published today in the journal Ecography, show that the true number may be surprisingly close to the upper end of that range. The researchers documented 60,000 unique species across the state, and they believe that represents just two-thirds of California’s true insect biodiversity. “I was surprised by how dramatic some of our findings are!” co-author Megan Barkdull, assistant curator of entomology at the Natural History Museum of Los Angeles County, told Gizmodo in an email. “We knew that California would have a very diverse insect fauna, since it’s a global biodiversity hotspot. However, I didn’t expect that every single ecoregion would be home to a starkly different insect fauna.” The quest to catalog California’s insects The statewide survey was carried out by the California Insect Barcode Initiative (CIBI), which is developing a publicly available DNA barcode reference library for all California insects. When you scan the barcode on an item at the store, the checkout system searches a database for the matching barcode and returns information about the item, like the price. DNA barcoding works the same way—a database of genetic information for different species allows scientists to identify individual organisms. Three of the insect species found in the Mojave ecoregion, uploaded as observations on iNaturalist. From left to right: Agriphila attenuatus uploaded by Nathan; Viridiseptis marina uploaded by Cricket Raspet; Polycesta aruensis uploaded by Andrew Meeds. Image credit: Courtesy of the Natural History Museum of Los Angeles County Building this database requires scientists to collect and identify every insect species in California. More than 100 people volunteered to participate in this massive undertaking, collecting tissue samples from museum collections and setting Malaise traps in 72 ecoregions—geographic areas where ecosystems and environmental conditions are generally similar—across the state. Malaise traps are large, tent-like structures that capture insects when they fly into their mesh walls, then move up the tent and into a collecting vessel filled with ethanol. This preserves the insects so they can be studied, Barkdull explained. In addition to gathering samples from these traps, she and her many colleagues employed various sampling methods at 454 other sites across California. Essentially every site they studied had a unique insect community, which is defined both by the types of species and the relative abundances of those species found at each location, Barkdull explained. “So, each site will have some insects that aren’t really found in other places, and even for the species that can be found in other sites, they’ll either be much more or much less abundant,” she said. Geographic distribution of potential richness estimate for insects across California. Image credit: 2026. Baker et al. Estimated species richness—the total number of species within a given geographic area—was highest in the Southern California Mountains ecoregion and the Mojave Basin and Range ecoregion, though the study notes that these estimates will evolve as the researchers continue to address sampling gaps. All told, the researchers barcoded more than one million specimens, and a preliminary completeness analysis suggests the more than 60,000 species they identified represent just 65% to 69% of California’s insect fauna. That means roughly a third of the state’s insect species remain undiscovered. A call for conservation The findings help close the gap between the estimated number of insect species in California and those that have been described—a gap that exists all over the world. “Across the globe, insects are poorly studied, especially compared to other, bigger animals like birds and mammals,” Barkdull said. “Many insects are tiny, live in obscure habitats like the soil, the treetops, or on other animals. As a result, there are without a doubt thousands of undiscovered species in the United States.” Studies indicate that insect populations are declining across the globe, but in many regions, there is still too little data to know exactly how steep those declines are. This new data, accessible via the Barcode of Life Data System, can help answer this question in California. Barkdull also hopes the findings will drive home the importance of explicitly considering insects when making conservation decisions. While many conservation tools—such as California’s Areas of Conservation Emphasis maps—are based on vertebrate and plant data, this study shows that patterns of insect diversity can vary widely from these groups. “That means we can’t use them as proxies when making decisions that aim to conserve this critical portion of our biota,” Barkdull said.