A small fly rediscovered near Paris has become an unusually vivid symbol of a much larger scientific problem. Pocota personata, a bumblebee-like insect last recorded in France roughly 150 years ago, was spotted again in the Paris region in 2025. Its return raises a basic but difficult question: did the insect vanish and reappear, or had it persisted unnoticed all along?
For biodiversity researchers, that uncertainty is not a curiosity at the margins. It is central to understanding the living world. Scientists can protect species only imperfectly when they do not know where those species are, how their populations are changing, or even whether a species has been formally identified. The challenge is likely to feature prominently as countries gather for the UN’s COP17 biodiversity summit in Armenia to assess progress on nature-protection commitments.
The scale of what remains unknown
Estimates cited by researchers show just how incomplete the inventory remains. A 2011 study estimated that 86% of terrestrial species and 91% of marine species had not yet been formally described. Even among species already known to science, conservation knowledge is uneven: in 2025, the extinction risk of only about 8% of known species had been assessed by the International Union for Conservation of Nature.
These figures matter because biodiversity policy depends on measurements. A country may know that biodiversity is declining overall while lacking enough reliable, long-running observations to determine which populations are falling fastest, where pressure is greatest, or whether an intervention has worked. That can leave officials and researchers with an incomplete baseline precisely when decisions on land use, habitat protection and restoration are being made.
The missing information is not distributed evenly. Large mammals and conspicuous birds are often easier to observe. Small insects, fungi and microscopic organisms are much harder to detect, distinguish and monitor. Tropical regions such as Borneo can be exceptionally rich in species while also being difficult to access. The result is a bias in what is visible to science: organisms that are small, hidden, remote or hard to identify can remain absent from datasets for long periods.
France builds a more usable record
In June, France’s National Museum of Natural History and the National Centre for Scientific Research launched Dynabiod, a project intended to build a database of the country’s plants and invertebrates. The aim is not simply to add names to a list. It is to assemble enough current and historical information to make changes in biodiversity more measurable.
Rodolphe Rougerie, who leads the project, described a gap between the broad understanding that biodiversity is declining and the ability to quantify that decline. Monitoring data from the past and present are often insufficient, especially for less visible groups of organisms. A national database could help connect observations that otherwise remain scattered across field records, collections and research projects.
The work begins with the unglamorous mechanics of sampling. At the Jardin des Plantes in central Paris and 16 other locations, researcher Fanny Kratz checks large white tents used as insect traps. The samples are then examined using DNA to help fill gaps in the record. The process is slow and technically demanding. A single trap can contain as many as 261 kinds of DNA, and a genetic trace does not automatically provide a complete answer about the species that produced it.
Why DNA does not remove the hard part
DNA-based monitoring can expand the reach of biodiversity surveys, particularly when samples contain many organisms that would be difficult to identify one by one. But it does not eliminate the need for careful interpretation. Researchers must connect genetic material to reference information and account for the fact that a trace can reveal presence without fully describing abundance, behavior or the condition of a population.
That makes cataloging life both a technical and institutional task. It requires repeated fieldwork, taxonomic expertise, reference collections, laboratory analysis and systems that preserve observations in forms other researchers and policymakers can use. It also requires continuity. A one-time survey may reveal what is present at a location; long-term monitoring is what makes it possible to see whether that picture is changing.
From rediscoveries to better decisions
The reappearance of Pocota personata is a reminder that absence from the record is not necessarily evidence of absence in nature. A species can go undetected because it is rare, seasonal, difficult to identify or simply not being looked for in the right place. Conversely, a lack of monitoring can delay recognition that a population is genuinely in trouble.
That distinction carries practical consequences. Conservation targets are often stated in broad terms, but implementation depends on information detailed enough to guide action. More comprehensive databases can help reveal where knowledge is weakest and where additional sampling would make the greatest difference. They can also make future assessments less dependent on guesses drawn from a narrow set of well-studied species.
Cataloging the world’s species will not be finished quickly. The work is painstaking by design, and the unknown is still vast. But projects such as Dynabiod show why biodiversity science is not merely about discovering unusual organisms. It is about building the evidence needed to tell whether the natural systems on which people depend are recovering, holding steady or disappearing before they are fully understood.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
