11 of the Smallest Mammals in the World

extremely tiny monkey clasping human fingers

bluedogroom / Shutterstock

In the biological world, it seems as though bigger would be better. And while it's true that bigger often means stronger (therefore able to outcompete smaller species), it also means more resources are needed to sustain the extra mass, and you can just forget about being inconspicuous. Smaller animals are better at hiding, accessing tight spaces, climbing upon the flimsiest of branches, and occupying ecological niches that larger animals simply can't.

They're also cute. Who could resist a bat barely bigger than a human fingernail or a lemur that weighs a single ounce?

Discover 11 of the world's smallest mammals.

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Etruscan Shrew

Etruscan shrew on metal surface sniffing the air

Lies Van Rompaey on iNaturalist / Wikimedia Commons / CC BY 4.0

There are many tiny shrews, but this pipsqueak takes the cake as the smallest. The Etruscan shrew is the smallest mammal in the world by mass. On average, it weighs less than .14 ounces and has a body length of about 1.57 inches.

For such a tiny animal, however, it has a huge appetite, typically eating about twice its own body weight every day.

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Pygmy Jerboa

tiny mouselike creature with long legs and long tail

reptiles4all / Shutterstock

Pygmy jerboas make up the rodent subfamily Cardiocraniinae and are the smallest rodents in the world. Their bodies start at two to three inches long, and their tails measure up to three inches.

For their size, these minuscule mammals sure can jump. Jerboas have kangaroolike legs that allow them to leap distances far exceeding their body lengths, an adaptation that helps them move quickly over the vast, arid deserts in Northern Africa and Asia that they call home.

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Bumblebee Bat

closeup of hand holding tiny bumblebee bat

Merlin Tuttle's Bat Conservation

The bumblebee bat, also known as Kitti's hog-nosed bat, is the world's smallest bat and the mammal with the smallest skull size. Weighing around .07 ounces (less than a penny) and with a length of 1.14 inches, it's so small that you might confuse one for a bumblebee if it went buzzing by your ear in the night.

Unfortunately, its delicate size is also indicative of its biological status. The IUCN lists the animal as near threatened, and a few roosting populations are at risk of extinction due primarily to human activity.

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Mouse Lemur

Mouse lemur hanging onto a branch in the forest

Michel VIARD / Getty Images

These adorable creatures are the world's smallest primates, measuring up to 11 inches in length including their tails. The smallest species is the Madame Berthe's mouse lemur, which measures just about 3.5 to 4.3 inches in length and weighs only about an ounce.

These softball-sized omnivores eat alone and mostly dine on "honeydew," a sugary byproduct of insect digestion. However, despite spending their foraging time alone, they do sleep with other mouse lemurs about half the time.

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Least Weasel

Least weasel stopped on a footpath in grassy conservation area

Carol Hamilton / Getty Images

This finicky, wise little weasel is the smallest species of the Carnivora order, making it the tiniest true carnivore in the world. North American least weasel males only reach seven inches, and the females grow to 5 inches. It weighs less than 1.5 ounces.

It might be hard to imagine something so small being such a cunning hunter, but the lesser weasel is the worst nightmare of any small rodent it encounters. They exhibit a much bigger, more ferocious personality than their small size might suggest.

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Pygmy Possum

Two pygmy possums on branch at night

TED MEAD / Getty Images

Ranging in length between two and four inches and often weighing barely over .35 ounces, these mini marsupials are found hanging upside down in trees in Australia and New Guinea.

IUCN lists one species, the Mountain Pygmy Possum, as critically endangered. This species has a limited habitat in the alpine areas of Australia. Ski resorts, road construction, and extensive bushfires have led to habitat destruction. The migratory Bogong moth makes up a significant portion of its diet and carries arsenic from pesticides in breeding grounds to the mountain. Scientists believe this is one factor leading to the decreasing population.

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African Pygmy Mouse

Two African pygmy mice playing on fake wood in enclosure

PapaPics / Getty Images

Mice are known for their small size, but the African pygmy mouse takes that trait to the extreme. Measuring 1.2 to 3.1 inches in length and weighing as little as .11 ounces, it is the world's smallest mouse. It is so petite that it typically stays hydrated by licking dew off tiny pebbles that it cleverly stacks in front of its burrow.

Some people keep these elfin mice as entertaining pets. Owners must remain hands-off with them, though, as they are incredibly fragile.

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Pygmy Marmoset

Pygmy marmoset resting on wooden platform in jungle

Jenhung Huang / Getty Images

Occasionally referred to as the "pocket monkey," these adorable, curious animals native to the Amazon rainforest are the world's smallest monkeys. Pygmy marmosets rarely exhibit a length greater than about 5.12 inches and typically weigh 4.37 ounces.

Their diet is as unique as their size. They use their sharp teeth and nails to gouge holes in trees and eat the sap, gum, and resins found inside. They also consume insects.

Evolutionary biologists from the University of Salford released a study in February 2018 announcing the pygmy marmoset is actually two different species: one that lives in the north Amazon River area and the other in the south.

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Long-Tailed Planigale

Long-tailed planigale on red sand

Alan Couch / Flickr / CC by 2.0

Native to Australia, long-tailed planigales are the world's smallest marsupials. They weigh less than .15 ounces and reach lengths averaging 2.32 inches, including the tail.

Their small size and flattened heads allow planigales to squeeze into crevices and cracks any other mammal would find impossible. This ability enables them to find food and to hide from predators. Their pouches face toward the rear to keep it clean as they navigate these crevices.

These fierce nocturnal carnivores hunt insects and even young mammals almost as large as themselves.

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American Shrew Mole

Two shrew moles on forest floor

Owen Borseth / Wikimedia Commons / CC BY-SA 4.0

The smallest species of mole in the world is the American shrew mole. This tiny mammal measures 4.72 inches long, including the tail, and weighs about .35 ounces. The American shrew mole doesn't even have external ears and has minuscule eyes that are almost invisible.

Found in the U.S. Northwest and Canada's British Columbia, these adorable underground dwellers have smaller front paws than most other moles, a trait that is similar to a shrew. These moles travel in groups of 11 or more and spend more time above ground than other moles.

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Pen-Tailed Tree Shrew

Small brown and grey tree shrew sitting on tree branch

Paul J. Morris / Flickr / CC BY-SA 2.0

The smallest tree shrew in the world is the pen-tailed tree shrew, which can weigh as little as 1.41 ounces and measure barely more than 5 inches. They appear so closely related to primates that there is debate as to whether to class them as primates or insectivores. Instead, they belong to their own order: Scandentia. The pen-tailed tree shrew is the sole member of its genus.

Sometimes known as a party animal, the primary diet of the nocturnal pen-tailed tree shrew is fermented alcohol from the bertam palm. It consumes amounts equivalent to 12 beers a day but never gets intoxicated. It also eats insects and small geckos.

What Are the Ecological Advantages of Being Small?

Being small can be a burden and a boon at the same time. While bigger animals tend to have more energy (thanks to faster metabolic rates), more speed, and greater fighting power against predators, small animals are better at tucking into tiny crevices and hiding. They don't need as many resources, so they don't have to do as much hunting.

In some cases, smaller animals also have better reproductive efficiency and access to a wider variety of food. One study says small carnivores are better at responding to "environmental emergencies" than their larger counterparts.

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