3,400 Wasp Species, One Tiny Forest: Why Scientists Think We've Been Undercounting Insects All Along

Before this episode even got started, host Regina Barber asked her co-host Scott Detrow a question: how many species of insects are there on Earth? Detrow thought it over. "Four million?" Nate Rott, sitting right there, needled him: "Well, you didn't go over. I'll give you that."

Go ahead and guess your own number before you keep reading. Odds are, like Detrow, you're about to find out you guessed way too low.

A Wasp That Basically Takes Over a Caterpillar's Body

The real answer starts somewhere you've probably never heard of: a protected forest reserve in Costa Rica, and a wasp so small it's measured in millimeters.

These wasps have a name for what they do: they're called parasitoid wasps, and their whole survival strategy is blunt. They lay their eggs in or on other insects — caterpillars, for instance — and when the eggs hatch, the larvae eat their way through the host to grow. Grim enough for you? Guest host Scott Detrow said he once watched a wasp do exactly this to a cicada in his own backyard: "It was like Alien in real life... it blew my mind." Co-host Nate Rott's only response: "Life finds a way." Regina Barber jumped in with the reassurance nobody asked for but everybody needed: don't worry, these things aren't hatching out of human chests.

Insects Are Too Small and Too Similar to Count by Eye — So Scientists Read Their DNA Instead

Most species censuses lean on animals you can actually tell apart by looking at them — birds, beetles. But most insects are tiny and look nearly identical to each other, which makes old-school eyeball classification basically useless, especially for a group as wildly diverse and visually uniform as parasitoid wasps.

Quick decode: the research team — which included Cornell entomologist Melissa Guzman — used a different trick. They sequenced one specific stretch of DNA from the wasps, then ran statistical modeling to estimate how many species that DNA pattern actually represented. In plain terms: take a small sample you can measure, and use it to estimate a much bigger number you can't measure directly.

The result made jaws drop: just one subfamily of parasitoid wasps, in this one reserve, turned out to contain 3,400 different species. In Guzman's own words: "There's so much that we don't know, right? And I think it's humbling, just to get a sense of how much we have yet to discover."

6 Million or 20 Million? The Estimate Just Tripled

The researchers didn't stop at one reserve. They took the same DNA-plus-modeling approach and scaled it up to a bigger insect sample from the reserve, aiming at a much bigger question: how many insect species exist on the entire planet?

Before this study, the best estimate — based on studies of beetles — put the number at roughly 6 million. For comparison, even the most generous estimates of bird species top out around 20,000 — a 300-times difference.

The new study, published this week in the Proceedings of the National Academy of Sciences (PNAS), says that 6-million figure is a massive undercount. The real number is at least 14 to 20 million — up to three times what scientists previously believed. Here's the part that really stings: so far, humans have formally, scientifically described only about 1 million insect species total — not even a fourteenth of the new estimate's low end.

The episode doesn't treat that new number as settled fact, though. Rott is upfront that this kind of modeling carries "a lot of uncertainty," and confirming the estimate would take a lot more taxonomic work — which makes sense, given that scientists have only formally described about 1 million insects so far.

Quick decode: what does "formally described" even mean? It's not enough to snap a photo and give something a nickname — a scientist has to study the species in detail, document exactly how it differs from everything else, and publish that in a research journal before it counts as officially "on the books." A million sounds like a lot, until you realize that if the new estimate holds up, somewhere between 13 and 19 million more insect species are out there with no official name at all — quite possibly sitting on a leaf in your own backyard, just waiting for someone to actually study it.

Side Note: The Same Episode Also Covered Ancient "Fireflies" and Cattle-Eating Wolves

This episode was actually a biweekly science news roundup, and insects were only one of three stories. Barber and Rott also covered the Euclid space telescope — launched by the European Space Agency in 2023, built to scan huge swaths of sky looking for rare objects — which just found 31 ancient quasars from the early universe. And they covered wolves that migrated from Oregon into California, whose main food source turns out to be cattle rather than deer or elk, simply because California doesn't have much wild prey left. Barber even used the fact that quasar light takes billions of years to reach us to call them "really, really old fireflies" — her segue for stitching two completely unrelated stories together in one breath.

Notable Details and Trivia

• Barber and Detrow both named the firefly as their favorite insect, independently of each other — Barber said she never saw one on the West Coast until she moved east, and the two of them joked, "Let's get firefly tattoos."
• Detrow's opening guess of "4 million" — the one Rott teased him about — turns out to have been low by a lot. Even against the new estimate's most conservative floor of 14 million, he was off by more than two-thirds.
• Production credits: produced by Rachel Carlson and Jordan-Marie Smith; edited by Rebecca Ramirez and Christopher Intagliata; fact-checked by Tyler Jones.

So, How Many Insect Species Actually Are There?

Back to the opening question — and honestly, nobody can give you a number carved in stone. Even this study, the one that just tripled the estimate overnight, calls itself the best guess available right now, not the final word.

Maybe the most interesting part of science isn't what it's already figured out, but what Guzman put into words: there's still an enormous amount that hasn't been counted, hasn't been found, and doesn't even have a name yet, quietly sitting in some forest most of us will never hear of. Next time you spot some unremarkable little bug in your backyard, consider this — there's a real chance it doesn't have a name at all, and no scientist has ever studied it either.