When reading the children’s classic Frog and Toad recently, I wondered what the difference between the two really is. Do frogs live more in the water and toads more on land? And what about other animals that seem similar, like rabbit and hare or turtle and tortoise? Are there actual differences between them?

To learn more, I asked Yoel Stuart, a graduate student at Harvard who studies Anolis lizards and has “an interest in all sorts of critters and how to identify them in the field.” 

“In some cases, it’s not a nice satisfying black-and-white answer,” he explains. “In many cases, the difference is semantic or historical. There’s not a real scientific difference.”

For example, the fuzzy line between mice and rats doesn’t follow scientific categories exactly. While “true” rats are of the genus Rattus and “true” mice are of the genus Mus, in common speech we use the term rats to describe larger rodents of various species that “eat more, take up more space, leave bigger droppings, and seem inherently scarier,” Stuart says, while we use the term mice to describe smaller rodent species that we think look cuter, regardless of genus.

In other cases, one term describes a subset (or family) of a larger group. Frog and toad fit this model. “All toads are frogs,” Stuart explains. “But not all frogs are toads.” Toads tend to have shorter legs than other frogs; to have drier, bumpier skin; to have poison glands behind their eyes; and—as I first guessed—to live in dry environments as well as wet ones. 

Similarly, the tortoise is a subgroup of turtle (a family within the order). Tortoises live on land more, have higher-domed shells, tend to live longer, and are more herbivorous than other turtles.

Rabbits and hares also are in different scientific families, but it’s harder to see the distinction. Hares have longer ears, longer legs, can jump farther, and have never been domesticated, as some rabbits have. “They look more wild,” Stuart says. If you see their babies, the difference becomes obvious: Hare offspring are “precocial,” meaning they are born with fur and are “able to see and fend for themselves right away.” Rabbits are born “altricial,” blind and hairless, and are cared for by their mothers.

But just as science starts making sense of these distinctions, the common language mixes them up again. “Jackrabbits are really hares,” Stuart points out. “A horned toad is actually a lizard.” So don’t get too caught up in the common names, he suggests; it’s more important to enjoy observing the natural world, in all its variety.