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I’ll show you some creatures, and you decide whether they’re the same or different species. Ready? Let’s start with these two butterflies.

They look completely different, so they’ve got to be two separate species, right? Nope. They’re the same!

How about these birds? They look almost identical, so you might think they’re the same species. But no again!

Species identification is hard, and scientists struggle with it as much as everyone else. Animals undergo dramatic transformations as they progress through different life stages. And sometimes, the differences between species aren’t visible to the human eye.

So we gathered a few of the most dramatic cases of mistaken identity over the centuries, including a snail that scientists misidentified more than 100 times. [♪ INTRO] All eels, regardless of whether they’re fresh or saltwater, s tart their lives way out in the open ocean looking very little like the adults they’re going to become. For starters, they are completely see-through. In fact, the juveniles look so different from the adults that, for a long time, scientists put these transparent babies into their own genus, Leptocephalus, commonly known as glass eels.

These babies can get big – over 20 centimeters in length – so it’s easy to see how they were mistaken for adults since they are like adult-sized! It wasn’t until they were raised in captivity that scientists found out that glass eels were actually just juvenile eels. The eels in captivity slowly transformed from a see-through ribbon to the colorations we’re more familiar with - from the brilliant blues and yellows of a moray eel to the silvery green-brown of an American river eel.

These babies traverse miles of open ocean as translucent juveniles to escape being a predator’s snack, only transforming closer to their final destination. Which makes them pretty hard to pick out of a lineup on their way. Figuring out whether a creature is a baby or an adult is easier if you can raise it in captivity.

But for creatures that live in the deeper parts of the ocean and don’t handle aquarium life very well, it can be very difficult. Like this next creature who stumped researchers for more than a century. It was discovered when people started finding a horned, armored creature in the stomachs of dolphins and tuna, earning it the nickname monster larvae..

The only thing that researchers knew about it was that it was a larval crustacean and not an adult – they just hadn’t found the adult form yet. The ocean is big, after all That’s because larval crustaceans often take on bizarre shapes that look nothing like their adult counterparts. I mean, look at this crab nauplius.

Does that look much like a crab to you? As the baby crustaceans grow and change, they begin to look more and more like their adult forms. Now researchers couldn’t raise the monster larvae in a lab to see who it would become because it was very rare to find any examples of it alive at all – ocean trawls were turning up next to nothing.

Not to mention it probably wouldn’t have survived, because it lives in deep, cold waters. But when a single specimen was pulled out of a mid-water trawl in the early 2000s, researchers finally had the opportunity to run a genetic analysis on it, revealing that this elusive, monstrous-looking baby grows up to be a beautiful ruby-red deep sea shrimp! Another creature that puzzled scientists for decades is the sunburst butterfly.

For over 100 years, the males and females had researchers convinced they were completely different species in completely different genuses! That’s because the sunburst butterflies exhibit sexual dimorphism – where the males and females of the species are significantly different from each other in some way, whether it’s size or color or something else. In the case of this butterfly, the males are a bright iridescent blue color.

But we couldn’t find any females until a paper published in 2018 by an international team of butterfly researchers began to study this drab butterfly assigned to a different species. By collecting short segments of gene sequences from butterflies and comparing them to each other—a process called DNA barcoding —researchers are able to determine how closely related two species are. And when they compared the bright blue and the drab butterflies, they found that the DNA of the latter was identical to that of the former!

Thankfully, for the sake of reproduction, the butterflies are better at telling who’s who than humans are. This next creature might win the prize for longest case of misidentification. It took almost 150 years for this bee to be correctly identified, and for that time period it was thought to be the rarest in the world.

Collected in the 1870s, the bee was classified as the only member of the genus Brachymelecta. It was particularly puzzling because researchers could never find another one like it. Its abdomen was covered in pale hairs, and parts of its wings looked different from other bees.

But in 2019, a researcher was examining this specimen and noticed that the veining pattern on the wings of the rare bee was the same as that of bees from a more common species called the California digger-cuckoo bee. Such a name, wow! Thanks to DNA barcoding, the rare bee was confirmed to be just an unusual example of the digger-cuckoo bee.

The pale hairs on the abdomen that made it stand out as unusual were believed to be a case of partial albinism. Not only that, after rummaging in another researcher’s bee collection, another pale-haired specimen was discovered and confirmed to be another unusual version of the digger-cuckoo bee. Some luck!

Man, the best thing I’ve ever found while rummaging was five bucks. This next species has been described by many as the world’s least-known bird species, because basically nothing was known about the large-billed reed warbler for almost 140 years. A single live bird was first collected in northwest India in 1867, and then another wasn’t seen again until 2006 in Thailand.

The 2006 discovery, along with the increasing popularity of genetic techniques, renewed researchers' efforts to learn more about this bird. Scientists began reviewing the DNA and size of warblers in museum collections and found that some large-billed reed warbler specimens, collected as far back as the early 1900s, were accidentally mislabeled as Blyth’s reed warblers. And I mean, yeah, I can see how you’d make that mistake.

Not only did the discovery help researchers learn a lot more about these birds, it significantly expanded the map of their breeding grounds into several new locations, as most of the birds in the collections were believed to have been collected during the mating season. And this bird can now relinquish its title of the world’s least-known bird! Which brings us to the long-suffering snail I mentioned at the beginning of the video.

This is a periwinkle snail. And so is this. And so is this.

Same species. No joke. You’ve probably encountered these snails on the beach at low tide.

They are anything but rare. However, that hasn’t stopped them from being misidentified over and over and over again throughout history. They’ve been quote unquote discovered as a different species or subspecies by scientists more than 100 times since they were originally described in 1792.

This confusion stems from their numerous shapes and colors, plus early researchers just assumed they didn’t get around much outside of their home range. These snails are native to the Atlantic, with a range that extends from the Arctic to the Mediterranean. But they’ve successfully made their way around the world, sneaking into the ballast water in the hulls of ships and even rafting along the surface of the ocean.

And just one snail is all it takes. Say a fertilized female gets whisked away to a remote island… whoops, a new colony is formed. And their environment plays a large role in why they look so different.

Take waves for example. Snail shell shape depends on the amount of wave activity in their environment - by varying the thickness and height, they can get protection from crashing waves. So two snail populations separated by a small distance may look completely different if one spot is more protected from waves than the other.

Once again, genetic analysis revealed the truth – while the appearance of these snails varies widely, their genes say they are all the same species. And now for a twist on today’s theme – two species that were mistaken for one. You might remember these birds from the top of the show, and if you didn’t recognize them as two species, you’re not the only one.

Closely related species of tanagers look almost identical when viewed in regular light. But under ultraviolet or UV light, there are actually some pretty dramatic differences in their markings. The wavelength of light that humans can see is around 400 to 700 nanometers, while UV wavelengths range from 100 to 400 nanometers, outside of our visible range.

But many birds can see near-UV light, which is in the 320 to 400-nanometer range, and researchers believe that markings visible in this wavelength help them identify each other in the wild. Unfortunately, researchers often use feather variations to describe different bird species, which can become an issue if they are only using human-visible light to look at patterns. So the old saying is true.

You really can’t judge a tanager or reed warbler or digger cuckoo bee by its cover. These few examples prove that species identification is as hard for scientists as it is for the rest of us, and that lots of people have gotten it wrong throughout history. And that’s okay!

Because thanks to the advent of new technologies like DNA barcoding, we have new ways of revealing the truth. Let’s just hope we never get that poor snail wrong again. Okay, so you can’t judge a book by its cover.

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