This time of year, with cicadas screaming, mosquitos buzzing, and grasshoppers chewing up the garden, it can be hard to believe the steady stream of news reports saying that insects are really declining. If you thought that, it turns out that you’d even be right – in a way.
Insects, including the pollinators our food supply depends on, really are in dire straits. Their numbers are dropping, and more and more species are becoming endangered and going extinct. A recent scientific study, though, shows that there may have been many more insect species all along than we thought – three times more, in fact!
The old estimate, around six million species, already sounds like a lot. The new study blasts it out of the ballpark, though, at somewhere between 14 and 20 million.
Think for a minute about how we even know how many species there are. Scientists count all the different species they can find – but new ones keep turning up all the time, so it stands to reason that there are probably some rare ones that any given survey is going to miss.
To account for those missing species, the researchers develop statistical models – an “undersampling ratio” – to estimate how many species are still lurking out there uncounted. If we found this many, the reasoning goes, there must actually be this many more hiding in the shadows.
Working in a nature preserve in Costa Rica, researchers set up traps for flying insects, focusing on a family called Microgastrinae, a well-studied group of small parasitic wasps. Since the group is already well-known, a deep dive into the number of previously undiscovered species in it should yield a more accurate undersampling ratio.
Captured insects were processed in an automated system that assigned them to species based on DNA “barcodes.” The researchers counted the species, applied the undersampling ratio, and then scaled it up from the nature preserve to the entire planet.
There are plenty of assumptions that go into this process, hence the wide range – from 14 to 20 million – of the estimated number of insect species. But the study authors are confident that the old number was far too low.
What does this mean for biodiversity conservation?
There’s a definite parallel in this to the perennial conundrum of whether the glass is half-full or half-empty. It can feel reassuring to know that there are more insect species out there than we thought, as a bigger buffer against the ongoing wave of extinctions. On the other hand, though, it means there are that many more species that scientists must race to discover, lest they go extinct before humans ever even know they’re there.
Ultimately, whether there are six million insect species or sixty, our best recommendations for conserving them remain the same: spray less insecticide, and plant more habitat!
The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).
