13 of the Most Populous Animals on Earth

The most populated animal in the world is probably not a single familiar species. The strongest published global estimate identifies soil nematodes as Earth’s most abundant animals: about 4.4 × 10²⁰, or 440 quintillion, live in surface soils. Ants are another exceptionally numerous animal group, with a conservative estimate of about 20 quadrillion individuals. Among domesticated vertebrates, chickens lead with more than 26.5 billion alive at a given time.

No scientifically defensible list can rank every animal species from first to last. Some figures describe broad groups, others describe individual species, and many marine or microscopic animals have never received a global census. This comparison therefore ranks 13 animals and animal groups with large, published estimates while showing the scope, date, and uncertainty behind each number.

Key takeaways

• Soil nematodes are the best-supported answer at the group level: a 2019 global model estimated 440 quintillion in surface soils.
• Ants number about 20 quadrillion: the estimate combines field studies from ecosystems worldwide and is considered conservative.
• Chickens are the most numerous domesticated vertebrates: global stock exceeded 26.5 billion in 2023.
• Humans are the most numerous primates and mammals counted with high precision: the United Nations estimated 8.16 billion people in mid-2024.
• Population does not equal biomass, ecological importance, climate impact, or conservation security. Those are separate measurements.

Population data last checked in July 2026. Livestock figures use 2024 FAOSTAT stock data where available; the human figure uses the United Nations’ 2024 population revision.

How to read this ranking

A population estimate is only meaningful when its scope is clear. Before comparing the numbers, keep four distinctions in mind:

• Group versus species: “soil nematodes” and “ants” include many species. Humans, house sparrows, and red-billed queleas are individual species. See what biologists mean by a species for the taxonomic context.
• Model versus census: microscopic and wild animals are estimated from samples and statistical models. Humans and livestock are tracked through national reporting systems, although those data also contain reporting error.
• Point-in-time stock versus annual total: a livestock stock figure estimates how many animals are alive at one time. It is not the number born, raised, or slaughtered during an entire year.
• Seasonal versus stable counts: short-lived animals and migratory birds can rise or fall sharply after breeding, migration, drought, disease, or changes in food supply.

The order below is approximate. Several estimates overlap, especially among the billion-plus wild birds and livestock populations. The list is most useful as a scale comparison, not as a precise league table.

The 13 animals and animal groups with the largest published estimates

Approximate rank	Animal or group	Published population estimate	What the figure represents	Confidence
1	Soil nematodes	440 quintillion	Many nematode species in global surface soils; 2019 model	High for the defined group
2	Ants	20 quadrillion	All ants globally; 2022 synthesis	High for the defined group
3	Chickens	More than 26.5 billion	Domesticated chicken stock in 2023	High
4	Humans	8.16 billion	United Nations mid-2024 estimate	High
5	House sparrows	About 1.4–1.6 billion	Wild species estimate; method and date vary	Medium
6	Cattle	1.58 billion	FAOSTAT global stock in 2024	High
7	Red-billed queleas	Up to about 1.5 billion	Seasonal post-breeding estimate	Low to medium
8	Sheep	1.36 billion	FAOSTAT global stock in 2024	High
9	European starlings	About 1.3 billion	Global wild-bird model published in 2021	Medium
10	Goats	1.19 billion	FAOSTAT global stock in 2024	High
11	Barn swallows	About 1.1 billion	Global wild-bird model published in 2021	Medium
12	Pigs	962 million	FAOSTAT global stock in 2024	High
13	Water buffalo	212 million	FAOSTAT global stock in 2024	High

1. Soil nematodes

Estimated population: 4.4 × 10²⁰, or about 440 quintillion, in surface soils.

Nematodes are microscopic roundworms found in soil, freshwater, oceans, plants, and animals. A 2019 study in Nature used 6,759 georeferenced soil samples to model their global distribution. The researchers estimated that 440 quintillion nematodes inhabit the world’s surface soils and described them as the most abundant animals on Earth.

This is not a count of one nematode species. It covers a vast assemblage of species and feeding groups, including plant feeders, bacterial feeders, fungal feeders, predators, and omnivores. The study also estimated their combined biomass at roughly 0.3 gigatonnes.

Nematodes matter because they connect soil food webs and influence decomposition and nutrient cycling. Their huge headcount does not make them a major direct cause of climate change. Instead, they are part of the living soil processes that researchers need to represent more accurately in carbon and nutrient models.

2. Ants

Estimated population: about 20 quadrillion ants.

A 2022 study in the Proceedings of the National Academy of Sciences synthesized ant-density records from ecosystems around the world. Its conservative estimate was 2 × 10¹⁶ ants, equal to roughly 2.5 million ants for every human counted in the United Nations’ 2024 population estimate.

The study estimated ant biomass at about 12 megatonnes of dry carbon. Ants dig and mix soil, disperse seeds, move nutrients, prey on other invertebrates, and become food for many species. Their distribution is uneven: tropical forests and savannas generally support far more ants than colder or heavily disturbed environments.

As with nematodes, “ants” is a group-level answer rather than a single-species answer. Thousands of ant species contribute to the global total, and sampling gaps mean the true number may be higher.

3. Chickens

Estimated population: more than 26.5 billion chickens alive at a given time in 2023.

Chickens are the most numerous domesticated birds and the most numerous domesticated vertebrates. The figure comes from livestock-stock reporting rather than an annual production total. Because broiler chickens have short production cycles, the number raised over a full year is much larger than the point-in-time stock.

The global chicken population is a product of human food systems, selective breeding, feed production, housing, disease control, and international supply chains. It should not be compared with a wild-bird estimate as though both were measured in the same way.

Chicken-related climate impacts arise mainly from feed cultivation, energy use, manure management, land-use change, processing, and transport. Chickens do not produce enteric methane at the scale of cattle, sheep, or goats, but a very large industrial population still has material environmental and animal-welfare consequences.

4. Humans

Estimated population: 8.16 billion in mid-2024.

The United Nations World Population Prospects 2024 estimated the human population at 8.16 billion in 2024. Humans are primates, mammals, and animals; this biological classification is explained further in why humans are animals.

Human population figures are more precise than most wildlife estimates because governments conduct censuses, register births and deaths, and maintain demographic models. Even so, the world total is an estimate rather than a simultaneous headcount.

Humans are not the most numerous mammals if uncertain rodent estimates are accepted, but no global rat or mouse census is comparable in quality to human demographic data. More importantly, human climate influence cannot be inferred from headcount alone. Fossil-fuel use, land conversion, industrial production, consumption patterns, technology, and inequality determine emissions far more than a simple population ranking.

5. House sparrows

Estimated population: roughly 1.4–1.6 billion.

The house sparrow (Passer domesticus) is one of the world’s most abundant wild bird species. A 2021 global bird-abundance model estimated about 1.6 billion individuals, while conservation assessments have published ranges that extend to roughly 1.4 billion. These figures are not contradictory so much as method-dependent.

House sparrows have expanded far beyond their original Eurasian and North African range, often alongside agriculture, buildings, grain storage, and deliberate or accidental introductions. Their close association with people helps explain their global reach.

A large worldwide population can conceal regional decline. House sparrow numbers have fallen in parts of Europe and other urbanized regions, showing why a global total cannot replace local monitoring, trend data, or habitat assessment.

6. Cattle

Estimated population: 1.58 billion cattle in 2024.

FAOSTAT’s Crops and Livestock Products data reported approximately 1.579 billion cattle worldwide in 2024. The category combines cattle reported by national statistical systems and should be read as a global agricultural stock figure, not a wild-animal estimate.

Cattle have a much larger average body mass than the animals above them in this headcount ranking. That difference is one reason biomass can tell a very different story from population size.

Cattle also have a disproportionate climate footprint within livestock systems because ruminant digestion produces methane. Manure, feed production, land use, energy, and supply-chain practices add further emissions. The impact per kilogram of food varies widely by production system, so the global headcount should not be used to judge every farm or region in the same way.

7. Red-billed queleas

Estimated population: up to about 1.5 billion after breeding.

The red-billed quelea (Quelea quelea) is a small seed-eating bird found across much of sub-Saharan Africa. It is often called the most numerous undomesticated bird because its post-breeding population may rise to around 1.5 billion.

That number is much less precise than a livestock stock or human population estimate. Queleas form enormous, mobile flocks; breed in response to rainfall and grass-seed availability; and can experience rapid seasonal mortality. A peak after successful breeding is not the same as a stable year-round population.

Quelea flocks can damage cereal crops, creating difficult tradeoffs for farmers and wildlife managers. Control programs have killed large numbers of birds, yet broad geographic range and high reproductive output allow the species to remain abundant. The example shows how population management, food security, animal welfare, and ecosystem function can come into conflict.

8. Sheep

Estimated population: 1.36 billion sheep in 2024.

FAOSTAT reported approximately 1.363 billion sheep worldwide in 2024. Sheep are kept for meat, milk, wool, hides, and livelihoods across environments ranging from humid pasture to dry rangeland.

Like cattle and goats, sheep are ruminants. Their digestive systems produce methane, while grazing management, feed, manure, land condition, transport, and processing shape the rest of the production footprint. Well-managed grazing can support some grassland objectives, while overgrazing can reduce vegetation cover and soil condition. Local ecology and stocking rates matter.

The stock figure also masks rapid turnover and regional concentration. It tells us how many animals countries report, not how those animals are distributed among production systems or what conditions they experience.

9. European starlings

Estimated population: about 1.3 billion.

The European or common starling (Sturnus vulgaris) was one of three species placed above one billion individuals by the 2021 global bird-abundance model. The model combined eBird observations with species-level information to estimate abundance for about 9,700 bird species.

European starlings are native to Eurasia and North Africa and have been introduced elsewhere, including North America, Australia, New Zealand, and South Africa. They use farmland, grassland, parks, and built environments, and can form large communal roosts.

The 1.3-billion figure should be treated as a model output with wide uncertainty, not a literal census. It is useful for comparing orders of magnitude, but conservation assessments and regional surveys remain better tools for tracking local trends.

10. Goats

Estimated population: 1.19 billion goats in 2024.

FAOSTAT reported approximately 1.188 billion goats worldwide in 2024. Goats provide milk, meat, fiber, hides, manure, and income, particularly in smallholder and dryland systems where other livestock may be harder to maintain.

Goats are adaptable browsers, which can be beneficial when controlled grazing manages brush or supports mixed farming. High stocking pressure can also suppress tree and shrub regeneration, especially in fragile drylands and on islands. The effect depends on density, timing, fencing, vegetation, and management rather than on the species alone.

As ruminants, goats emit methane through digestion. Their global climate effect is smaller than cattle’s in absolute terms but still relevant within food-system emissions.

11. Barn swallows

Estimated population: about 1.1 billion in the 2021 global model.

The barn swallow (Hirundo rustica) has one of the broadest ranges of any land bird. It breeds across much of the Northern Hemisphere and migrates to Africa, southern Asia, Australia, and the Americas.

Its estimated billion-plus population reflects global modeling rather than direct counting. Other conservation sources use lower mature-individual estimates because they apply different definitions and evidence. That disagreement is a useful warning: a population number can change substantially depending on whether it includes immature birds, how observations are converted to density, and which year or season is represented.

Barn swallows feed on flying insects and often nest on human structures. Agricultural intensification, pesticide use, fewer insects, and loss of nesting sites can drive local declines even when the species remains globally widespread.

12. Pigs

Estimated population: 962 million pigs in 2024.

FAOSTAT reported approximately 962.4 million domestic pigs worldwide in 2024. As with chickens, this is a stock figure. Short production cycles mean the number of pigs raised during a year is higher than the number alive at one moment.

Pigs are non-ruminants, so they do not produce enteric methane in the same way cattle, sheep, goats, and buffalo do. Their environmental footprint instead depends heavily on feed production, manure storage and treatment, energy, land use, water, and supply chains.

National disease outbreaks, trade restrictions, feed prices, and consumer demand can change pig populations quickly. A dated source is therefore essential whenever this number is used.

13. Water buffalo

Estimated population: 212 million water buffalo in 2024.

FAOSTAT reported approximately 212 million buffalo worldwide in 2024, most of them domestic water buffalo in Asia. They are raised for milk, meat, hides, manure, and draft power, and they remain economically important in many smallholder farming systems.

Water buffalo are ruminants, so methane from digestion is part of their climate footprint. Production intensity, diet, manure handling, animal health, land management, and milk or meat output all affect emissions per unit of food.

This final position does not mean no other animal exceeds 212 million. Dogs, cats, rats, mice, pigeons, copepods, krill, mites, springtails, and many other animals may do so. They are omitted because a current, globally comparable estimate is unavailable, too broad, or methodologically weaker than the figures used here.

Why exact animal populations are hard to calculate

Scientists rarely count every individual. They sample a fraction of a population and extrapolate using habitat area, detection probability, density, distribution, and life-history data. Each step adds uncertainty.

• Small animals are easy to miss: soil, leaf litter, deep water, and sediments contain enormous populations that are difficult to sample consistently.
• Wildlife moves: migration, dispersal, and shifting food or water sources can produce double counting or missed animals.
• Populations turn over: births, deaths, harvesting, disease, and seasonal breeding can change a count within weeks.
• Taxonomy changes: what was once treated as one species may be split into several, altering historical comparisons.
• Data systems measure different things: livestock statistics, wildlife population models, mature-individual assessments, colony counts, and biomass estimates answer different questions.

That is why unsupported claims such as “there are seven billion rats” should not be repeated as fact. A plausible-sounding number is not a substitute for a transparent method.

Does a large animal population mean a large climate impact?

No. Headcount alone is a poor measure of climate impact. A population’s effect depends on body size, metabolism, diet, lifespan, land use, feed, manure, energy, technology, and the wider system that supports it.

• Humans: human activities are the cause of modern global warming, but emissions vary enormously by income, energy source, infrastructure, consumption, and policy.
• Ruminant livestock: cattle, sheep, goats, and buffalo produce methane during digestion. Feed, manure, and land use add further emissions.
• Poultry and pigs: these animals have different digestive emissions, while feed production, manure, energy, and supply chains remain important.
• Wild invertebrates: nematodes and ants participate in decomposition, soil formation, and nutrient cycling. Their ecological processes can affect carbon movement, but describing them as causes of climate change would be misleading.

The more useful question is not “Which abundant animal causes climate change?” but “Which human systems produce greenhouse gases, and how do animals fit within those systems?” See how climate change affects animals for the other side of the relationship.

Why familiar animals such as dogs, cats, rats, and pigeons are not ranked

Global estimates for free-roaming dogs, owned pets, feral cats, commensal rodents, and urban pigeons often combine incompatible surveys or repeat figures without a clear date and method. Those animals may number in the hundreds of millions or more, but their ranges are too uncertain for a source-ranked list.

Marine animals present an even larger evidence gap. Copepods, krill, and other zooplankton can occur at immense densities, yet abundance is usually reported by volume, area, biomass, or regional survey rather than as a defensible global count of individuals. Excluding them is not a claim that they are scarce; it is an acknowledgment that the available measurements are not directly comparable.

Population size does not guarantee conservation security

A species can remain globally abundant while declining rapidly in part of its range. It can also have many individuals concentrated in a narrow habitat, making it vulnerable to disease, climate extremes, invasive species, or land-use change.

Conservation assessments consider trend, geographic range, fragmentation, mature individuals, and extinction probability—not headcount alone. Our guide to extinction-risk categories explains why “common” and “secure” are not interchangeable.

The reverse is also true: numerical abundance is not the same as ecological importance. Some rare predators, pollinators, seed dispersers, and ecosystem engineers have effects far beyond their headcount. Explore animals with outsized ecological roles for examples.

The most useful answer

If someone asks, “What is the most populated animal in the world?” the clearest evidence-based answer is: soil nematodes are the most abundant animals in a published global group estimate, at roughly 440 quintillion in surface soils. Ants number about 20 quadrillion. Chickens lead among domesticated vertebrates, and humans are the most numerous primates.

The larger lesson is that population figures are not interchangeable. A useful comparison names the taxonomic scope, method, date, and uncertainty—and keeps headcount separate from biomass, conservation status, welfare, and climate impact.

Frequently asked questions