Small talk World's tiniest creatures present a new frontier for biological discoveries

In the 19th century, the German zoologist Christian Bergmann pondered a question: why are some animals so small? His answer, that a warm-blooded animal’s size increases as its habitat cools, is still a rule in biology today.

- Patrick Greenfield

“Bergmann pointed out that smaller species tend to live in warmer climes,” said Dr Simon Loader, the principal curator of vertebrates at the Natural History Museum. “This pattern is to do with surface area and volume: smaller animals lose heat faster and struggle to maintain their body temperature when it is very cold. Whatever the reasons, these small species are fascinating .”

With so much of life on Earth still unknown, scientists are discovering new tiny organisms every year, redefining what is considered the smallest of their kind – and some claims about which are the smallest of them all are hotly contested.

Smallest reptile Brookesia nana, nano-chameleon, Madagascar 

First described as a species in 2021, a male Brookesia nana is just 20mm (0.8in) long and is found in the rainforests of northern Madagascar. Females are larger, growing to nearly 30mm. Researchers believe it is critically endangered, found in an area severely degraded by deforestation.

Despite its overall size, Brookesia nana is considered remarkable because of its disproportionately large male genitals, known as hemipenes in snakes and lizards.

“The miniaturized males may need larger hemipenes to enable a better mechanical fit with larger females,” said Loader.

Madagascar is famous for its small animals, including several miniaturized frogs and Madame Berthe’s mouse lemur, the world’s smallest primate.

Smallest bird Mellisuga helenae, bee hummingbird, Cuba