In the 19th century, German zoologist Christian Bergmann pondered a simple question: why are some animals so small? His answer, that the size of a warm-blooded animal increases as its habitat cools, remains a rule of biology to this day.
“Bergmann pointed out that smaller species tend to live in warmer climates. This pattern is related to surface area and volume: smaller animals lose heat more quickly and struggle to maintain their body temperature when it is very cold,” says Dr Simon Loader, the Natural History Museum’s chief curator of vertebrates. “Whatever the reasons, these little species are fascinating,” he says.
With much of life on Earth still unknown, scientists discover new tiny organisms every year, redefining what is considered the smallest of their kind – and some claims about who is the smallest of them all are hotly contested .
Small creatures can sometimes struggle to get the same conservation attention as their larger, charismatic counterparts. “The small varieties are often overlooked or missed,” says Paul Rees, nursery manager at Kew Gardens. We asked scientists to tell us about the smallest creatures of their kind.
Smallest reptile: Brookesia nana nano chameleonMadagascar
First described as a species (discovered by science) in 2021, a male Brookesia nana is only 20 mm long – the size of the head of a matchstick – and is found in the rainforests of northern Madagascar. Females are larger and grow to almost 30 mm. Researchers believe the world’s smallest reptile is critically endangered, found in an area severely affected by deforestation.
Despite its overall size, Brookesia nana is considered notable for its disproportionately large male genitalia, known in snakes and lizards as hemipenes.
“The miniaturized males may require larger hemipenes to allow for better mechanical fit with larger females,” says Loader.
Madagascar is known for its small animals, including several miniaturized frogs and Madame Berthe’s mouse lemur, the world’s smallest primate.
Smallest bird: the bee hummingbird, Cuba
The bee hummingbird (Mellisuga helenae) weighs as much as a paper clip and is only 5-6 cm long. The eggs are mainly found in dense forests and on the edge of the forests of Cuba. The eggs are the size of a coffee bean and their wings beat 80 times per second. Due to habitat destruction on the Caribbean island, scientists are concerned about its survival.
“The population is thought to be declining by 20-29% per decade due to forest loss and degradation, and has already disappeared from many areas where it was previously widespread,” said Dr Ian Burfield, BirdLife International’s global science coordinator. .
“Like other hummingbirds, it feeds on nectar from a range of flowering plants and plays an important ecological role as a pollinator, so its decline is doubly concerning,” he says.
Smallest insect: Dicopomorpha echmepterygis, a parasitic wasp, USA
The smallest insect in the world is so small that it is smaller than some single-celled organisms. The American parasitic wasp is only 0.139 mm long and spends most of its life inside its host, the bark louse.
“A kind of ‘fairy fly’, these are small wasps that develop as parasitoids, laying their eggs inside the eggs of bark aphids, which themselves are not too large,” says Dr Gavin Broad, chief curator of entomology at the Natural History Museum. .
“One female wasp develops inside the host egg and eats most of its contents, accompanied by one to three males, which are wingless, have rudimentary heads and are generally simplified because they never leave the egg; they are just there to fertilize females,” says Broad.
Smallest amphibian: Paedophryne amauensis frogPapua New Guinea
This little frog is so small that it has no tadpoles. The frog, described in 2012, lives in leaf litter in the rainforest and feeds on ticks and mites.
“Unlike many other frogs, its life cycle does not include the aquatic tadpole stage. Instead, tiny frogs hatch directly from eggs laid in moist leaf litter on the forest floor,” said Dr. Jeff Streicher, chief curator of herpetology at the Natural History Museum. “Adults feed on small invertebrates found in the same leaf litter. This lifestyle is common in other small frog species, highlighting the essential role that leaf litter microhabitats play in the survival of these small amphibians.”
Smallest mammals: Etruscan shrew and the bumblebee bat
For mammals it is difficult to distinguish between two small contenders. The Etruscan shrew, found in parts of Eurasia and North Africa, weighs on average between 1.2 grams and 2.7 grams. It is solitary and mainly active at night feeding on invertebrates. The little shrew has a short life and rarely survives its second winter, says Paula Jenkins, chief curator of mammals at the Natural History Museum.
The other miniature mammal considered the smallest in the world is the bumblebee bat, also called the pig-nosed bat, which is found in two isolated populations in Thailand and Myanmar. It also weighs about 2 grams, with a wingspan of up to 145 mm and a body length between 29 mm and 33 mm.
“It roosts in extensive caves in limestone outcrops near rivers,” says Jenkins. “Individuals stay separately at some distance from each other. They hunt invertebrates in the upper forest canopy using echolocation to detect their prey in flight, and can also pluck prey from the foliage.
Smallest flowering plant: Wolffia globosaoriginating from Asia but found all over the world
Also called duckweed, Wolffia globosa has the fastest known growth rate of any plant and can quickly cover entire bodies of water. Despite lacking common plant organs such as leaves, roots and stems, it produces the smallest known fruits and is highly nutritious.
Tom Pickering, the senior greenhouse manager at Kew’s Royal Botanic Gardens, says the plant is weedy in appearance and nature. “This vigorous, free-floating aquatic plant is grown in tanks at the tropical nursery at Kew and is used worldwide for animal feed, medicine and food. Despite its size, Wolffia belongs to the same plant family as the Titan Arum, a flowering plant with the largest inflorescence in the world,” he says.
Smallest fish: it depends who you ask…
The title of the smallest fish in the world is hotly contested. According to Guinness World Records, the male is 6.2 mm Photocorynus spiniceps, a species of deep sea devil found in the Philippine Sea that is sexually parasitic. It attaches to the much larger female – a trait common in anglerfish – essentially turning her into a hermaphrodite. She feeds, swims and ensures their survival – he only worries about reproduction.
But considering the female Photocorynus spiniceps is several times larger than the male, other researchers say the title at the Paedocypris progenetica from Sumatra, which swims around peat swamps and grows up to 7.9 mm as an adult. The tiny Indonesian fish was scientifically described in 2006 and declared the smallest – a claim that was quickly disputed by researchers studying the anglerfish.
Smallest cactus: Blossfeldia liliputanaArgentina and Bolivia
The Blossfeldia liliputanaThe nickname comes from the word ‘lilliput’, which means a small person or creature, explains Paul Rees, nursery manager at Kew Gardens. “It also refers to the imaginary land inhabited by little people in Gulliver’s Travels,” he notes.
Found on rock faces and in high altitude cracks in Bolivia and Argentina, it can withstand extreme drought and lose up to 80% of its moisture content. Despite their versatility, the world’s smallest cactus is increasingly threatened by collectors.
“Over the years this species has been sought after by collectors, and due to its very slow growth rate, a number of plants have been poached from the wild. Although its wide distribution means it is listed as ‘least concern’, poaching remains the biggest threat to this species.”
Smallest fungi: waiting to be discovered
After the little one Mycena subcyanocephala was photographed in Taiwan last year and went viral on social mediaSome incorrectly said it was the smallest in the world. But with an estimated two million species of fungi waiting to be discovered, there are likely many microscopic organisms still waiting to be discovered, says Ester Gaya, senior research leader in mycology at Kew Gardens.
“Mycena subcyanocephala is one of the smallest species of fungi in the world. Regardless of their small size and ethereal appearance, this species of fungus plays its role in nature’s complex recycling system. Mycena species are saprobes, meaning they feed on decaying organisms and help rid our forests of unwanted ‘litter’.”
With important roles ranging from nutrient recycling to carbon sequestration, she says, “Like all the little things, it’s often the coordinated work of multiple tiny fungi that has a big impact on our ecosystems.”