Hares and rabbits look similar, and some may hop to the conclusion that they're the same animal.

Not so fast. Our Weird Animal Question of the Week comes from Tristan Ishtar, who asked: "What's the difference between a rabbit and a hare? And is that where 'hare brained' came from?"

The short answer: A lot, and yes—the adjective "harebrained" likely refers to hares' skittish tendencies, especially in captivity.

Hares and rabbits are in the same family, Leporidae, but they're "different species, like sheep and goats are different species," Steven Lukefahr, a geneticist at Texas A&M University in Kingsville, said via email.

View Images Young eastern cottontails (Sylvilagus floridanus) snuggle in their nest. Photograph by Scott Camazine, Alamy

Opposites From Birth

Hares are also larger, have longer ears, and are less social than rabbits. The "most profound difference" is seen in baby hares versus baby bunnies, said Philip Stott, a wildlife ecologist at the University of Adelaide in Australia. (See National Geographic's pictures of baby animals.)

First off, a hare's pregnancy lasts 42 days, compared with rabbits' 30-31 days with a bun(ny) in the oven.

Newborn hares, called leverets, are fully developed at birth—furred with open eyes—while newborn rabbits, called kittens or kits, are born undeveloped, with closed eyes, no fur, and an inability to regulate their own temperature, Stott said.

Their nests are also worlds apart—"hares live completely aboveground, lacking the normal burrow or warren system of rabbits," said Michael Sheriff, an ecologist at Penn State in University Park, Pennsylvania. (Related: "Ask Your Weird Animal Questions: Animal Nests Explained.")

That's why, as a hare that burrows, "Bugs Bunny is a fraud," Stott joked.

There is an exception to the burrowing-bunny rule—the cottontail, a type of American rabbit that does not burrow.

View Images A female European hare (right) boxes with a male in Wales. Photograph by Andy Rouse, 2020VISION/Nature Picture Library/Corbis

Are We Fair to the Hare?

As for "harebrained," which means flighty or foolish, Stott suspects it stems from the animals' unease in captivity, where they're prone to spooking at the slightest stimulus (sometimes accidentally causing their own deaths).

Stott, who has tried hand-raising hares, said even those that are bottle-fed from day one never really relax in his company.

The expression "mad as a March hare" is no doubt a reflection on hares' behavior during mating season, which involves leaping into the air, among other antics, Texas A&M's Lukefahr said.

The female hare, called a jill, tests the male, called a jack, by making him give chase over several miles, Stott says. If he catches her, she'll mate with him; if not, "he was poor paternal material anyway," Stott says. (Also see "Wild Romance: Weird Animal Courtship and Mating Rituals.")

But if a female isn't ready to mate with a male who is chasing her, she might stand up and throw a punch right at him—or several.

Life in the Fast Lane

Such a zany courtship is not just about fun—it's also about staying fit, Stott said.

Speed is crucial to hares' survival, especially for species that live on open plains, such as the European hare, which can run at 37 body lengths a second, he said. Cheetahs, he noted, "can only manage 23 body lengths per second."

Those speedy reflexes may be great for avoiding predators, but it makes hares a "poor pet," he said. That's another way they differ from rabbits, which the American Society for the Prevention of Cruelty to Animals describes as "delightful companion animals."

Despite its name, a jackrabbit wouldn't make a good pet, either. It's called that because of its fabulous ears, which reminded its namers of a jackass, but it's not even a rabbit. It's a hare.

Your mind has to be as quick as a bunny to keep these animals straight.