by In the 19th century, the German zoologist Christian Bergmann considered a simple question: why are some animals so small? His answer is that a warm-blooded animal increases in size as its habitat cools, a rule in biology to this day.
“Bergmann pointed out that smaller species tend to survive in warmer climates. This pattern is related to surface area and volume: small animals lose heat faster and struggle to maintain their body temperature when it’s very cold,” says Dr Simon Loader, head curator of vertebrates at the Natural History Museum . “Whatever the reasons, these little species are fascinating,” he says.
With much of Earth’s life still unknown, scientists are discovering new tiny organisms every year, redefining what is considered the smallest of their kind – and there are several claims about who is the smallest of them all being hotly contested.
Small creatures sometimes struggle to get the same conservation attention as their larger charismatic counterparts. “The smaller species 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, male Brookesia nana it’s only 20mm (0.8in) long – the size of a chipmunk’s head – and is found in the rainforests of northern Madagascar. Females are larger, growing to nearly 30mm. Researchers believe the world’s smallest reptile is critically endangered, found in an area severely degraded by deforestation.
Despite its overall size, Brookesia nana is considered notable for its oversized male genitalia, known as hemipenes in snakes and lizards.
“The miniaturized males may require larger hemepods to enable a better mechanical fit with larger females,” says Loader.
Madagascar is famous for its small animals, including several miniature frogs and Madame Berthe’s mouse lemur, the world’s smallest primate.
The smallest bird: the hummingbird, Cuba
The bee hum (Mellisuga helenae) weighs as much as a paperclip, and is just 5-6cm (1.9-2.3in) long. Found mainly in dense forests and woodland edges in Cuba, its eggs are the size of a coffee bean and its wings beat 80 times a second. Due to habitat destruction on the Caribbean island, scientists are concerned about its survival.
“Its population is thought to be declining at a rate of 20-29% over the past decade due to forest loss and degradation, and it has already disappeared from many areas where it was once widespread” says Dr Ian Burfield, global co-ordinator Science BirdLife International. .
“Like other hummingbirds, it feeds on nectar from a range of flowering plants and plays an important ecological role as a pollinator, so reducing it is a double concern,” he says.
Smallest insect: Dicopomorpha echmepterygis, parasitic wasp, USA
The smallest insect in the world is so small that it is smaller than some single-celled organisms. As small as 0.139mm in length, the parasitic US wasp spends most of its life inside its host, the wasp.
“A species of ‘nymph’, these are tiny wasps that develop as parasites, with eggs laid inside the eggs of bark lice, which are not very large themselves,” says Dr Gavin Broad, chief curator of entomology at the Natural History Museum . .
“A single female wasp develops in the host egg, consuming most of the material, along with one or three males, which lack wings, have rudimentary heads and are generally simplified because they do not leave the egg never; they’re just there to fertilize females,” says Broad.
Smallest amphibian: Paedophryne amauensis frogPapua New Guinea
This tiny frog is so small it doesn’t have tadpoles. Described in 2012, the frog lives in the leaf litter of the rainforest, feeding on ticks and mites.
“Unlike many other frogs, its life cycle does not include an aquatic tadpole stage. Instead, tiny frogs hatch directly from eggs laid in moist leaf litter on the forest floor,” says Dr. Jeff Streicher, chief curator of herpology 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 of leaf litter microhabitats in the survival of these tiny amphibians.”
The smallest mammals: the Etruscan blind and the bumblebee bat
For mammals, it’s hard to separate two tiny competitors. The Etruscan sherd, found across parts of Eurasia and northern Africa, weighs an average of 1.2g to 2.7g. It is solitary and active mainly at night feeding on invertebrates. The little blind lives a short life, and rarely survives a second winter, says Paula Jenkins, senior curator of mammals at the Natural History Museum.
The other small mammal considered the world’s smallest is the bumblebee bat, also known as the pig-nosed bat, which is found in two isolated populations in Thailand and Myanmar. Also weighing around 2g, with a wingspan of up to 145mm and a body length of between 29mm and 33mm.
“It roosts in extensive caves in limestone outcrops near rivers,” says Jenkins. “Individuals feel distanced from each other. They hunt for invertebrates in the upper forest canopy using echolocation to detect prey in flight, and may also pick prey from foliage.”
Smallest flowering plant: Wolffia globosanative to Asia but found worldwide
Sometimes called duckweed, Wolffia globosa which has the fastest known growth rate of all plants and can quickly cover entire bodies of water. Despite the absence of common plant organs such as leaves, roots and stems, it produces the smallest known fruits and is highly nutritious.
Tom Pickering, senior manager of demonstration greenhouses at the Royal Botanic Gardens Kew, says the plant has the appearance and nature of a weed. “This vigorous free-swimming aquatic plant is grown in tanks in the tropical nursery at Kew, and is used around the world for animal feed, medicine and food. Despite its size, Wolffia is in the same 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 world’s smallest fish is the subject of much controversy. According to Guinness World Records, the male is 6.2mm Spiniceps Photocorynus, a species of deep-sea marine fish found in the Philippine Sea that is sexually parasitic. It attaches itself to the much larger female – a common trait in marine fish – making her a hermaphrodite. She feeds, bathes and ensures their survival – he only cares about reproduction.
But because of the female Spiniceps Photocorynus There are several times more than the man, other researchers say the title belongs to the Paedocypris progenetica from Sumatra, which swims around in peat bogs, growing up to 7.9mm as adults. 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 liliputanArgentina and Bolivia
The IS Blossfeldia liliputanThe epithet comes from the word ‘lilliput,’ which means a tiny person, explains Paul Rees, nursery manager at Kew Gardens. “It also refers to the imaginary land of tiny people in Gulliver’s Travels,” he notes.
Found growing on rock faces and in crevices at high altitude in Bolivia and Argentina, it can withstand extreme drought, losing up to 80% of its moisture content. Despite its versatility, the world’s smallest cactus is increasingly threatened by collectors.
“Over the years this species has been desired by collectors, and due to its very slow growth rate, some 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 tiny Mycena subcyanocephala in Taiwan last year and went viral on social media, some wrongly said it was the smallest in the world. However, with an estimated 2m species of fungi waiting to be discovered, there are probably many microscopic organisms waiting to be discovered, says Ester Gaya, the senior research leader in mycology at Kew Gardens.
“Mycena subcyanocephala one of the smallest fungal species in the world. Regardless of its minute size and ethereal appearance, this species of fungus plays its role in nature’s complex recycling system. The Mycena species are saprobes, meaning they feed on decaying organisms, helping to clear our forests of unwanted ‘trash’.”
With important roles from nutrient recycling to carbon sequestration, she says: “As with all small things, it’s often the coordinated work of multiple small fungi that has a big impact on our ecosystems.”
