Bison or buffalo? Possum or opossum? What's the difference?

© Photograph by Steve Gettle, Minden Pictures
A Virginia opossum (pictured in Michigan) is a far cry from the possums of the Pacific islands.

By Jason Bittel, National Geographic

Butterflies fly during the day, and moths come out at night. At least, that’s what conventional wisdom says. But is this a good way to tell the difference between butterflies and moths?

Not really, says Akito Kawahara, an entomologist and curator of Lepidoptera—the order of insects that includes butterflies and moths—at the Florida Museum of Natural History.

© Photograph by Bill Hatcher, Nat Geo Image Collection
A ringtailed possum climbs a tree in Mount Field National Park in Tasmania.

In fact, there are tons of moths that fly during the day, says Kawahara, as well as butterflies that come out at night. Take the family Hedylidae: These Neotropical insects seem to tick off all the moth boxes—their wings are covered in mottled browns, their antennae lack tiny clubs at the end, they’re nocturnal, and they have even evolved a hearing organ that helps protect them against bats. And yet…

© Photograph by Charlie Hamilton James, Nat Geo Image Collection
The American bison (above, an animal roaming the National Elk Refuge in Wyoming) is not closely related to true buffalo of Asia and Africa.

“It turns out that, using DNA evidence, we now know that they’re actually a butterfly,” says Kawahara, who is also an associate professor at the University of Florida.

If you want to get technical, butterflies are really just a small subset of specialized, day-flying moths. There are 160,000 known species of moths and butterflies, and only about 20,000 of those are butterflies.

“The bottom line is all butterflies are moths, and there's no such thing as butterflies,” says Kawahara.

You see, the more you look around the animal kingdom, the more examples of confusing nomenclature you’ll find—whether it’s turtles and tortoises or alligators and crocodiles. These sorts of divisions may seem trivial, but they can also be a learning opportunity. Too many people, says Kawahara, will appreciate a popular insect like the monarch butterfly, but not the wonderful things moths do.

© Photograph by Beverly Joubert, Nat Geo Image Collection
The African buffalo is the most populous herbivore in Africa. Above, an animal is seen in Botswana's Okavango Delta.

“They’re all amazing. Let’s look at the things we don’t typically look at,” he says, “because there’s so much we don’t know about the world.”

Toady frogs and froggy toads

Many people grow up learning that frogs have bright, smooth, shiny skin, and toads are characterized by drab, rough, wart-covered skin. But what of the South American harlequin toads, which sport an array of vibrant colors?

“There are many exceptions to the stereotypical, big, brown, bumpy toad,” says Jodi Rowley, curator of amphibian and reptile conservation biology at the Australian Museum Research Institute in Sydney and National Geographic Society Explorer.

And just as it’s fair to say all butterflies are moths but not all moths are butterflies, so can you say that all toads are frogs but not all frogs are toads.

There are 52 families in the order Anura, Rowley says by email. One of those families, Bufonidae, includes the “true toads,” which generally tend to crawl rather than hop, have bumpy skin, and display visible glands on their neck and shoulders.

But to really divine the difference, you must go inside the toad. For instance, most toads have what’s known as a Bidder’s organ in front of their kidneys, which helps regulate sex hormones. They also lack teeth in the upper and lower jaws, have fat bodies in their groins, and possess highly ossified skulls, says Rowley.

Bison, buffalo, and opossums, oh my

People commonly refer to these large horned beasts of the American prairies as “buffalo,” but they are actually “bison.” In fact, the animal’s scientific name, Bison bison, drives the point home twice.
While buffalo and bison are both mammals within the Bovidae family, the two are not all that closely related. So-called “true buffalo” include the African buffalo and water buffalo, native, respectively, to Africa and Asia.

In the same vein, it may seem as if the words “opossum” and “possum” can be used interchangeably. But opossum typically refers to the Virginia opossum and its cousins in the genus Didelphis, all of which live in North and South America. Conversely, possum refers to a suborder of tree-living marsupials native to Australia, New Guinea, and Sulawesi. These include honey possums, brushtail possums, and ringtail possums.

What’s in a name?

In some cases, discerning between two types of similar-looking creatures is important, as in the case of Australia’s invasive cane toad.

That's because people sometimes mistake toad-like native frogs for the invasive cane toads—leading to many well-meaning, but unnecessary, frog deaths.

It's worse for the predators that eat toads thinking they're frogs. Since predators haven't evolved to process cane toad toxins, accidentally eating one can be fatal.