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Home > Research & Collections > News > The Frog that Was a Pregnancy Test

The Frog that Was a Pregnancy Test

The Tale of the African Clawed Frog

The African clawed frog lives in Los Angeles for a very strange, urinal reason. Photo credit: C-Monster via Flickr.


With its welcoming climate, Los Angeles is home to untold numbers of introduced species — plants and animals that were brought here by people, sometimes on purpose and other times completely accidentally. They each have their own story, like the coqui frogs stowing away in nursery plants, exotic pet birds flying the coop, or escargot snails making a slow but steady bid for freedom.

But none has a story quite as bizarre as the African clawed frog. Seriously, brace yourself. These frogs, originally from Africa as the name suggests, were exported worldwide in the 40s and 50s because they were used as living pregnancy tests back then. Yes, before the over-the-counter stick was developed, labs used live animals to test for telltale hormones in a pregnant person’s urine. It turns out that African clawed frogs, if injected with human urine, produce eggs within about 12 hours if pregnancy hormones are present. At the time, this made for a very convenient pregnancy test, decades before more straightforward chemical tests were developed.

And yes, it sounds pretty grisly to inject frogs with pee, but it wasn’t lethal, so the frogs could be used over and over again for this test during their 30-year lifespan in captivity, which is partly why this was such a widespread practice. Before using frogs, some labs did essentially the same test with rabbits, but in that case, they checked to see if the urine injection made the rabbits’ ovaries enlarge. This required a dissection to check, however, so it killed the animal in the process. Checking a water tank for eggs was far easier, and no one had to perish.

a photo of an African clawed frog in the herpetology collections. it's in a tray and has a broad body and visible claws on its back legs
An African clawed frog in the NHM Herpetology Collections. Notice the claws on its hind feet that inspired this frog’s common name.

And so, as a living pregnancy test, these frogs were exported in huge numbers from Africa and kept in labs all over the world. When other pregnancy tests were developed that didn’t require a tank full of displaced amphibians, these frogs either escaped or were deliberately released. And here in Southern California, they’ve taken a liking to their new home and continue to thrive here decades later.

Back in 2015, Herpetology Curator Greg Pauly and a team of community scientists found a population of these frogs in a pond in the Gardena Willows Wetlands Preserve, which protects one of the very few remaining fragments of willow wetland, a type of habitat once common along the creeks and rivers that meandered across the L.A. Basin. Surrounded by city, the preserve is under constant threat from trash, vandalism, and introduced species, including these African clawed frogs.

a side by side photo of people using a net to catch frogs in a wetlands, and a photo of frogs in an orange bucket
Greg Pauly and SuperProject participant Darren Burke seine for African clawed frogs at the Gardena Willows Wetlands. Photos by Maiz Connolly.

The pond full of introduced frogs was subsequently drained, and later filled back up by water trickling down from a nearby street sewer. And recently, in October of 2018, Pauly and a team of volunteers found more frogs in the same spot, which means there might be more to this story.

“My guess is that there is an upstream source, or rather, upsewer source,” said Pauly. “These things might actually be living in the sewers of L.A. It’s the equivalent of the alligators in New York sewers, except we actually have them.”

And you might be wondering, “So what? Frogs are cool. What’s wrong with a different sort of them in Los Angeles?” And no argument about frogs being awesome; however, there are some definite drawbacks to introduced species. For one, they sometimes can compete directly with local frogs, eating their food (or even their young) and crowding them out of their homes. And worse, introduced frogs can also bring diseases with them, such as chytrid fungus, which has decimated amphibian species worldwide. In fact, African clawed frogs may have been a big player in the spread of this deadly fungal infection. And it’s not the frogs’ fault. It’s ours.

So if you ever find yourself buying a pregnancy test at the drugstore, be happy it doesn’t require frogs, and if you know anyone with exotic pets, make sure they don’t escape into the sewers (or anywhere else).


Pssst, if you want to learn more about African clawed frogs, come see a preserved specimen on display in the Museum’s upcoming temporary exhibition That was Then, This is Now, opening February 7, 2019.



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