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See The World's Tiniest Frogs - And Why Being So Small Is So Hard - BBC

20 February 2024

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Sarah Bregel

Features correspondent

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Brachycephalus pulex are now the smallest known vertebrates (Credit: Renato Gaiga)

Brachycephalus pulex might be the title holders for world's smallest vertebrate. But it's not easy being green – or tiny.

Scientists believe they may know what the world's smallest vertebrate is. A tiny, pea-sized Brazilian frog called Brachycephalus pulex (or, Brazilian flea toad, even though it is a frog) has the tiniest measurements, according to new research.

Back in 2011, Mirco Solé, a researcher at the State University of Santa Cruz in Brazil, was the first to investigate this species' size compared to that of other similar frogs. The sample wasn't large enough at the time to be conclusive, but the most recent research, in which Solé and his team measured the body lengths of 46 flea toads and confirmed the frogs' maturity and sex by examining their gonads and checking for the presence of vocal slits in their throats (which only males have), was more expansive. It found that male B. Pulex frogs measured in at just over 7mm (.28in). Females were slightly larger at just over 8mm (.31in). 

Mark D. Scherz, curator of Herpetology at the Natural History Museum of Denmark, says that this species of "impressively small" frogs is very likely the title holder for tiniest vertebrate in the world, and that the assertion "is backed up with a remarkably large dataset". Still, he maintains that while there is a lot of current evidence, it's not possible to know what lies ahead in terms of new discoveries. "It's definitely possible for the envelope to keep getting pushed," he says. 

Tiny vertebrates are notoriously hard to track, but experts say it's important (Credit: Getty Images)

That has been the pattern, after all. The record has continuously evolved, going to smaller and smaller species as more research has been done. "In the last 30 years," Scherz notes, "the record has gone from around 10mm (0.39in) (Eleutherodactylus iberia) to 6.45 (.25in) - 8.87mm (0.35in)" which is a more than 10% reduction in length.

Sherz says that although there are likely to be more tiny contenders for the smallest vertebrate title in coming years, that "small" depends on how the species is being measured. "If we take it as a linear measure, the frogs are currently clear winners," he explains. "But if we go by mass or volume, then fish would likely claim the title, as they are very narrow-bodied and slender, whereas the frogs are rather round." He imagines there are some tiny "planktonic fishes" that have not yet been discovered.

Those discoveries, and subsequent research to understand what makes these species unique and interesting besides their size, have their challenges when it comes to the smallest species, which is why pea-sized frogs are tracked in some unique ways. Some scientists have even introduced tiny tracking pants and other mini belt-like devices that the miniature vertebrates wear for a short time to help scientists better understand the way they move. 

Miniature frogs are so small they have trouble with balance (Credit: Mark D. Scherz)

Luci Kirkpatrick, a lecturer at the School of Environmental and Natural Sciences at Bangor University in North Wales, understands some of those challenges. She developed tracking devices that fit some smaller animals. She says they are traditionally tough to track, but that doing so is massively important for conservation. While small animals are tiny, they're abundant "ecosystem engineers" who she says are "critical in making sure the food web functions properly".

As the tiniest vertebrates around, B. Pulex frogs face their own difficulties – in addition to being difficult to monitor accurately. They struggle to do something frogs are supposed to be inherently good at: jumping. In fact, 2022 research found that these miniature vertebrates actually lose their balance when they leave the ground. They're simply so tiny that they can't make proper use of their vestibular systems, which help control stabilisation.

These frogs may be small, and they may not always land on their feet, but experts say we should still keep tabs on what the tiniest creatures are doing. "Those populations can change quickly and respond to changes in the environment," which can be hugely positive, she explains. But a disease outbreak among the population could be catastrophic if not monitored, she says.

"If you want to conserve an animal, you need to know what it's doing," for better or for worse, Kirkpatrick explains.

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Green Frogs' Song Heralds The Arrival Of Summer

For most people, Memorial Day marks the first day of summer.

The official first day of summer is not observed until three weeks later, on June 20, but the three-day weekend gives people a chance to get outside, fire up the grill, or even go camping. In a past life, when I worked for a variety of different parks as a ranger, naturalist or law enforcement officer, it was Memorial Day that was always seen as "the beginning."

These days, I work as a teacher and the first day of summer is dictated by the nature of the winter we experienced during the school year. This year, due to very mild conditions, we will get out before the actual first day of summer, but not too much before. However, the arrival of hot weather last week certainly has me feeling like summer has arrived. This was especially true when I made my first visit to the "Thinking Chair" at the edge of my meadow.

WET, MILD WINTER

I arrived to find only a few changes. We hadn't received much snow during the winter, but what did fall was wet and heavy. As a result, many branches had come down off the trees that stand within range of my camera and I realized that I'd have to learn a new landscape. This will be easy, however, because no winter goes by without something changing.

The one thing that was impossible to miss was that the ground was extremely wet. This, after all, prevents trees from growing in the bowl-shaped depression at the "bottom" of the hill upon which my house is built. Certain grasses can deal with the water, but so far, no trees have been able to handle the conditions. I also recalled hearing the weather roundup on the radio during which it was mentioned that we are about 4 inches of rain above normal this year. The meadow was absolutely soaking wet.

FROGS ARRIVE

So, with my feet a little damp from my walk, I eased back into the comfort of my beloved chair and started taking notes. This bird here, that bird there, and so on. Then, to my absolute delight I heard the familiar sound of a green frog (Lithobates clamitans) coming from the meadow. Right in front of the Thinking Chair is the lowest point in the meadow. It behaves as the drain for the entire area. If there is any free water to be found, it will be found in this spot. On this day, there was a nice flow of clear water through the grass. The local frogs had found it to their liking.

I have never found bullfrogs in this habitat, but green frogs are a little more flexible when it comes to where they will spend their time. Green frogs seem to thrive, from high up in the wet meadow to further down in the woods, where a seasonal stream flows, Eventually, however, the water always dries up and the frogs are forced to move to nearby ponds that retain water throughout the year.

GREEN FROG'S SONG

The green frog's song is one that I have always thought of as being made by plucking the string of a banjo. I have no recollection if this was something I heard from another naturalist when I was young, or if this is my way of looking at things, but the banjo idea is firmly cemented into my mind. I suppose it doesn't hurt that Kermit the Frog (wow, I'm old) also played the banjo in The Muppet Movie. Why think of anything else, right?

I know there is at least one "pool" in the meadow where standing water can persist for quite some time and I am sure that females will lay eggs there every spring. The problem with this area is the water can dry up, which happens at different times on a year-to-year basis. The young frogs need 8-10 weeks for their legs to develop. That puts them on a schedule that can be pretty tight. I have seen small green frogs in the meadow in late summer, but I can't really be certain of where they came from.

So, I won't worry about it. Male green frogs do a lot of singing because they need to attract females. The males find decent habitat and then do their best to advertise the spot. Females will come around and either agree or disagree. This year, with a warm and rainy spring, the frogs are clearly at it already. But even without the notion of breeding, there is the simple joy of hearing the telltale splash of a frog jumping into the water when I approach the little drainage stream on my way to or home from the Thinking Chair. The bonus comes when I sit quietly for an hour and the frogs forget I am there. Then, the singing starts, and the feeling of summer spreads across the meadow.

Bill Danielson has been a professional writer and nature photographer for 26 years.  He has worked for the National Park Service, the U.S. Forest Service, the Nature Conservancy and the Massachusetts State Parks and has taught biology and physics at Pittsfield High School for 20 years. For more information, visit his website at speakingofnature.Com. 

It's Almost Giggin' Time!

Get your wader's ready and your flashlight batteries recharged because frogging season is about to begin.

The Missouri Department of Conservation wants Missourians to get ready for the season which begins sunset June 30 and ends Oct.

Damon Grosvenor

Damon Grosvenor is a reporter covering the Missouri Legislature and state government for the News Tribune. He can be reached at [email protected] or 573-761-0242.

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