Top 14 Largest Animal Swarms in the Animal Kingdom

Recently, scientists discovered a massive swarm of Argentine ants, so vast that it could nearly cover the entire globe. The largest colony stretches for almost 6,000 km along the Mediterranean coast.

Argentine ants, scientifically known as Linepithema humile, are native to Argentina, Uruguay, and Paraguay. They are an invasive species in many regions with a Mediterranean climate, including South Africa, New Zealand, Japan, Easter Island, Australia, Hawaii, Europe, and the United States. These ants displace native species and rapidly spread.

What sets Argentine ants apart is their unique behavior: unlike other ants, they do not fight one another when from the same colony. A single nest may contain multiple queens, a trait uncommon in other species, and one of the reasons they succeed in dominating the habitats of native insects.

Argentine ants have the potential to spread worldwide due to two key features: First, they can survive harsh winters by taking shelter in deep underground tunnels. Second, they are incredibly aggressive and resilient. While most ants live in harmony, even collaborating to find food, Argentine ants are relentless invaders, constantly attacking native ant colonies they encounter.

These ants destroy native ant nests, either forcing the residents out or killing them. Each assault involves tens of thousands of strong, combative ants. As a result, the steady advance of Argentine ants forces native ant species to retreat, except for honey ants.

Krill shrimp are small crustaceans that live in large, dense swarms. The density of individuals in these swarms can reach 10,000 to 30,000 per cubic meter. They are found in every ocean around the world, with the largest populations located in the Antarctic seas. A massive krill swarm can stretch up to 10 km in length and 30 meters in depth.

Despite their small size, krill are crucial to ocean ecosystems, with the largest concentrations found in the Antarctic. Overfishing of krill not only threatens ocean biodiversity but also disrupts fish populations and the global fishing industry.

Krill float with the current, using their bristled swimming legs to steer and filter food from the water, feeding on phytoplankton during the colder months and spring.

Although individual krill are small and vulnerable in the perilous ocean environment, large krill swarms are vital links in the marine food chain. They convert plankton cells into energy that supports a wide range of animals, from small fish to seabirds, and even the largest animals on Earth, such as the blue whale, which can consume up to 2,500 kg of krill a day.

Locust swarms, consisting of millions or even trillions of insects, are a nightmare for farmers. One of the largest locust swarms ever recorded occurred in North America in 1875. This swarm covered an estimated area of 500,000 km², roughly the size of California, and contained approximately 12.5 trillion locusts.

The record for the largest swarm in the animal kingdom belongs to locusts. In early 2020, a massive desert locust cloud swept across the skies of East Africa, stretching across thousands of square kilometers. "It looked like a black blanket covering the sky, so dense that it was difficult to see through the clouds," said researcher Emily Kimathi from the Insect Physiology and Ecology Centre in Kenya.

This event marked the largest locust swarm observed in the Horn of Africa in 25 years. Experts estimate that the swarm contained about 200 billion locusts, with a density of around 50 million locusts per square kilometer. Desert locusts are known for their rapid reproduction, capable of increasing their numbers 20-fold in just three months.

200 billion locusts is an astounding number, but historical data shows that locust swarms can grow even larger under ideal environmental conditions. In 1875, a meteorologist named Albert Child was astonished by a massive swarm of Rocky Mountain locusts that darkened the skies over much of the western United States. He estimated that the swarm covered an area of 512,800 km².

This historic event is now known as the "Albert's locust swarm." Based on Child's estimates, the swarm could have contained as many as trillion locusts, considered the largest recorded number of animals in a single swarm in human history.

A mature mayfly typically lives for only one to two days. Usually, all mayflies in a given area will develop almost simultaneously, gathering in large swarms that can cover the sky as they move. Due to their short lifespan, mayflies tend to group together to ensure reproduction. Of the nearly 2,500 species of mayflies worldwide, about 630 species are found in North America.

Mayflies are considered relatively primitive insects, exhibiting some ancient characteristics that were likely present in the first flying insects. The larvae of mayflies live in fresh water, typically in clean, unpolluted environments. The mayfly nymph can live for up to 3 years in water, but once they molt and emerge on land, their lifespan is reduced to only a few hours.

Plankton are drifting animals that range in size from tiny rotifers to visible jellyfish. The distribution of plankton is influenced by factors such as salinity, temperature, and the availability of food in their environment. The smallest plankton act as vital nutrient recyclers in the water column, playing an important role in enriching the ecosystem.

Larger plankton serve as crucial food sources for various fish species, as well as the larval stages of all fish. They also link primary producers (phytoplankton) with higher trophic levels in the food web. Plankton communities consist of two main groups: primary consumers that feed on phytoplankton, and secondary consumers that feed on other planktonic organisms.

The red-billed quelea is the most populous wild bird species in the world. When they gather in large flocks, these birds can cause significant damage to crops, much like the devastation caused by locust swarms.

Queleas primarily feed on seeds from annual grasses but also wreak havoc on cereal crops. For this reason, they are sometimes referred to as Africa's 'feathered locusts.' Common pest control methods include pesticide spraying or setting firebombs at night in their massive colonies. However, these widespread control efforts have largely failed to limit quelea populations. When food sources dwindle, these birds migrate to areas with recent rainfall and abundant grasses, making them highly efficient at exploiting food resources.

Often considered the most undomesticated bird species on Earth, red-billed queleas can sometimes reach a post-breeding population peak of around 1.5 billion individuals. They forage in immense flocks, with millions of birds. When the ones at the back of the flock run out of food, they fly to the front of the flock, creating the appearance of a swirling cloud of birds.

Red-billed queleas are also known for their elaborate and complex nesting habits, which may be the most intricate of any bird species. While some species display parasitic breeding behavior, their nests vary widely in shape, size, and materials used, depending on the species. Nesting materials include small leaf fibers, grasses, and twigs. Many species weave beautiful nests using thin leaf veins, though some, like the buffalo weaver, build large and somewhat haphazard nests using small twigs within their colonies, with several spherical nests interwoven. In Africa, red-billed queleas build ‘room-like’ nests, where 100 to 300 pairs of birds create separate chambers, entering through small tubes at the bottom. Most species construct their nests with narrow entrances that slightly angle downward.

Penguins, also known as flightless birds, are a group of aquatic birds that cannot fly. They are predominantly found in the Southern Hemisphere, with only one species, the Galápagos penguin, living north of the equator. Penguins are well adapted to life in the water, with contrasting plumage and flipper-like feet that aid in swimming. Most penguins feed on crustaceans, fish, squid, and other marine life they catch while diving. They spend about half their lives on land and the other half in the sea.

Although they are not the only creatures living in Antarctica, penguins are unique to the Southern Pole, not found anywhere else in the world. They thrive in such extreme conditions due to physical adaptations that help them survive the cold:

• Penguins can endure freezing temperatures thanks to a specialized coat of feathers that provides insulation, blocks wind, and shakes off water after they hunt. Contrary to popular belief, penguins have the densest feather coverage of any bird.
• Another key adaptation is the thick layer of fat provided by nature. On average, a penguin has around 30% of its body weight in fat, which helps it dive into the freezing waters.
• The third factor is their communal lifestyle. Penguins often live in large colonies, sometimes consisting of thousands of individuals, where they huddle together for warmth against the harsh Antarctic cold.

These physical traits and social behavior enable penguins to thrive in the extreme environment of Antarctica. Some might wonder why penguins don’t live in the Arctic, which, while cold, is still a more ideal environment for them. The answer lies partly in the fact that penguins cannot fly to escape predators like polar bears and arctic foxes, who hunt birds nesting in the area during the summer. In contrast, Antarctica offers them safety, with no natural predators, making it the perfect place for long-term settlement.

Bats (scientific name: Chiroptera) are the second largest order of mammals, with approximately 1,100 species, making up about 20% of all mammal species (the largest order, Rodentia, accounts for 40%). The name Chiroptera comes from Greek, where "cheir" (χειρ) means "hand" and "pteron" means "wing." As the name suggests, the forelimbs of bats resemble human hands, with the fingers connected by a membrane that forms the wings. (More precisely, a bat's wings are created by a membrane stretched between the arm bones and the fingers.)

Bats are the only mammals capable of true flight. While other mammals like flying squirrels or flying lemurs may seem like they can fly, they are actually only capable of gliding within limited distances. About 70% of bat species feed on insects, while the remaining species primarily eat fruits, with only a few species preying on meat. Bats play a crucial role in ecosystems by pollinating flowers and dispersing seeds, with the survival of many plant species entirely dependent on bats. The smallest bat species, Kitti's hog-nosed bat, is only 29–33 mm in length and weighs around 2 grams, while the largest species, the large fruit bat, has a wingspan of up to 1.5 meters and weighs around 1.2 kg.

Bats share many traits with insectivorous mammals, and can be considered an insect-eating branch of mammals that evolved to take to the skies. The forelimbs have transformed into wings, with long fingers (except the thumb) and a thin, hairless membrane stretching between them. This membrane also connects the forelimbs to the hind limbs and tail. Bats also have powerful chest muscles. Another distinctive feature of bats is their unique hanging posture, where they dangle upside down.

Bats use echolocation, emitting ultrasonic sounds at frequencies between 50,000 and 70,000 Hz. By interpreting these sounds in their ears, bats can gauge the distance to obstacles. However, they don’t rely solely on echolocation; they also use their vision while flying. Fruit-eating bats have highly developed vision, located at the top of their heads. In contrast, insectivorous bats have smaller eyes, which are mainly used for determining altitude, assessing light levels, distinguishing between day and night, and judging prey size and obstacles while flying in search of food.

A honeybee colony consists of a queen bee, drones, and worker bees. The queen bee measures between 20 and 25 mm in length, with short wings and a short stinger. Drones, the male bees, are around 15 to 17 mm in size. They lack stingers and have larger wings. Drones only serve one purpose: mating with the virgin queen. Worker bees are sterile females whose reproductive organs are underdeveloped, preventing them from mating. Worker bees are responsible for all the tasks in the hive: defending the colony, producing royal jelly to feed larvae, and collecting nectar to turn into honey.

In honeybee society, a few larvae are selected to become queens, while the majority develop into worker bees. Honeybees possess enzymes in their gut that can neutralize the toxic chemicals found in many pesticides used to control mites in beehives. They also have hair on their eyes to help them collect pollen. Honeybees have five eyes—three small ones on top of their head and two larger ones at the front. To produce just one teaspoon of honey, a bee needs to visit approximately 4,000 flowers.

Honeybees face threats from various predators, including viruses (which are a major cause of honeybee population decline), toxic fungi, and parasitic flies. One of the most dangerous threats is the parasitic fly Apocephalus borealis, which injects its eggs into the abdomen of a bee. After the larvae feed on the bee’s internal organs, they burrow through its body and emerge. There is also a growing body of research suggesting that honeybees originated in Asia, contradicting the previous belief that they came from Africa. Genetic analysis reveals that the earliest ancestors of honeybees lived in cavities and emerged from Asia about 300,000 years ago before spreading to Europe and Africa. This evolutionary tree based on genetic sequencing does not support the theory that honeybees came from Africa. The population of honeybees is also being affected by climate change. As the world’s top pollinators, honeybees are vital to the production of many crops—at least one-third of the food humans consume daily relies on pollination by honeybees.

Sardines, also known as pilchards, are small oily fish from the herring family. The name 'Sardine' originates from the Mediterranean island of Sardinia. These fish have elongated bodies with an oval shape, a blue or brownish back, and silver-colored bellies. Sardines feed on algae, fish eggs, larvae, and small shrimp. During the day, they live at depths of 30 to 60 meters, but at night, they rise to depths of 15 to 30 meters. Sardines possess an internal biological clock, similar to that of Western salmon. Sardine eggs hatch in freshwater, and the young fish grow in rivers before migrating to the sea. In spring, they return upstream to their birthplace to fulfill their reproductive duties.

Sardines are known for migrating in large schools, often numbering in the millions. They move swiftly through the ocean, creating breathtaking displays of synchronized motion. These schools of sardines are spectacular, twisting and turning as they move through the water. When faced with obstacles or predators, such as sharks, dolphins, whales, or birds of prey, the school swiftly changes direction, creating mesmerizing formations. To protect themselves from these large predators, sardines form massive, spherical groups that can stretch up to 20 meters in diameter, traveling together in unison with tens of millions of fish.

The migration of sardines is a natural phenomenon where they travel in concentrated waves, instinctively moving toward warmer waters. The sardine migration spans an impressive 15 km in length, km in width, and can reach depths of up to 40 meters. The scale of this migration is so vast that it can be observed from space. This stunning annual event is known as the 'Sardine Run,' a remarkable and awe-inspiring migration.

Zebras evolved from Old World horses around 4 million years ago. There is evidence to suggest that zebras are a polyphyletic species, and their stripes may have evolved more than once. Larger stripes are thought to be advantageous for zebras living in low-density desert environments (like donkeys and wild horses) or those in colder climates with thicker coats. However, molecular evidence suggests that zebras form a monophyletic group.

Researchers have used GPS tracking devices to monitor the migration patterns of eight zebra species from Namibia to Botswana over several months. Their migration spans up to 500 km in the Serengeti Wildlife Conservation Area, marking it as the longest known overland migration of any mammal species.

Additionally, scientists were astonished by the directness of zebra migrations, with their path being remarkably straight compared to other species that tend to follow winding routes. This straight-line migration often leads to longer travel distances than those of other wild mammals like antelopes, wildebeests, hyenas, and elephants.

The study also highlighted the detrimental effects of human activities on wildlife habitats, such as the construction of border fences, highways, and railways, which interfere with natural migration patterns. These disruptions make it more difficult for animals to find food and water, threatening their survival, especially in the face of unpredictable climate changes.

The monarch butterfly is a small insect with millions of individuals in each migration cycle. This species is the only butterfly known to migrate in both north-south and south-north directions, similar to birds. However, due to its short lifespan, no individual survives through the entire migration. They lay eggs throughout their journey.

Recent studies have expanded our understanding of the migration history of this butterfly species, with its striking orange and black wings. Initially, many scientists believed that migration only began recently. This misconception arose because most monarch butterflies outside North America are tropical and non-migratory. Scientists assumed that their ancestors were the same and began migrating only in the 19th century.

However, genetic research has shown that this migratory butterfly species originated over 2 million years ago. It was also found that the migration ability is linked to specific genes controlling wing muscle formation and function. These findings raise concerns about the future of this incredible migration, as monarch populations have dramatically declined. In 1996, billions of butterflies completed their north-south journey, but last year the number dropped to just 35 million. This decline is believed to result from deforestation, drought, and pesticide use on their main food source and egg-laying habitat: the milkweed plant.

Researchers hope that these findings will provide insights into how to preserve this migratory behavior for future generations of monarch butterflies.

During the rainy season, millions of red crabs on Christmas Island, Australia, migrate to the sea to begin their breeding season. Their migration starts from the island's forests and leads them to the shores of the Indian Ocean. The migrating crab population can range from 40 million to 120 million individuals. Throughout this migration period, roadblocks are set up to prevent traffic and pedestrian movement in various locations.

The indigenous inhabitants of Christmas Island rarely mention the red crabs. It is believed that the current large population of red crabs is due to the extinction of the Maclear's rat, a natural predator that once kept their numbers in check. Surveys estimate an average of 0.09–0.57 adult crabs per square meter, leading to an estimated total population of around 43.7 million red crabs across the island. Some estimates suggest up to 120 million red crabs on Christmas Island, but these figures are not definitively supported.

The introduction of the invasive Anoplolepis gracilipes ant has had a negative impact on the red crab population. It is estimated that approximately 10-15 million red crabs, or about one-third to one-quarter of the total population, have been killed by A. gracilipes ants in recent years. In total, around 15-20 million red crabs have been wiped out by this invasive species.

From October to December each year, as the rains begin, red crabs embark on their massive migration to the coastline for breeding. Each crab travels up to 8 kilometers over the course of 9 to 18 days. They are able to cover such a distance thanks to an increase in the production of a hyperglycemic hormone that boosts glucose levels in their blood, providing the energy needed for the long journey. Upon reaching the coast, female crabs mate with males in burrows prepared by the males, after which the females continue their journey to the sea to lay their eggs. Unlike other land crabs on the island, red crabs are the only species where males accompany the females during the migration to the sea.

Wildebeests are known for their massive herds, often numbering in the tens of millions. A single herd can stretch over 140 km in length. However, their numbers have dramatically decreased in recent years due to hunting, habitat loss, and disease.

In the Maasai Mara reserve, a population of non-migratory blue wildebeests dropped from around 119,000 in 1977 to just 22,000 by 1997. This decline is attributed to increasing competition between livestock and wildebeests for dwindling grazing land, which has been impacted by agricultural expansion and possibly changes in rainfall patterns.

The blue wildebeest exhibits both migratory and non-migratory behavior. In Ngorongoro, most of the population is sedentary, with males maintaining year-round territories, although reproduction follows a seasonal cycle. Females and calves typically form small groups of around 10 individuals, or sometimes merge into larger herds. Males without territories form bachelor groups. In ecosystems like Serengeti and Tarangire, wildebeests tend to migrate, with both males and females frequently on the move, although some smaller resident populations exist. During the breeding season, males may mark temporary territories for a few hours or even a day, attempting to gather females to mate, but must then move on to establish new territories.

Each year, certain populations of blue wildebeests in East Africa engage in long-distance migrations, timed with the rainy season and the growth of fresh grass. Their migration patterns can vary significantly from year to year, depending on the length of the rainy and dry seasons. As the dry season ends (around May or June in East Africa), wildebeests leave dry areas in search of water. When the rains return (a few months later), they quickly return to their former range. Factors influencing this migration include food availability, surface water sources, predators, and the phosphorus content in the grass.

Schooling is a common behavior in fish species, but herring form the largest schools of any fish. Studies have shown that herring schools can number in the tens of millions, covering areas as large as tens of square kilometers. They gather in these vast schools to reduce the risk of predation or to focus on breeding seasons.

Herring are similar in shape to anchovies but are larger in size. They have bluish-green skin, small bones, and a long, slender body with symmetrical jaws. Herring have small or no teeth, thin, round scales that easily shed, and some species even have comb-like scales along their bellies. Herring typically migrate in large schools. They inhabit the surface waters and have no real hiding places, with their slender bodies and powerful tails allowing them to swim swiftly.

In the wild, herring are a staple prey species for many predators such as seabirds, dolphins, sea lions, whales, sharks, tuna, cod, and other large fish. Herring are particularly important for the diet of bald eagles. They are among the few fish species that survived the mass extinction event at the end of the Cretaceous period, continuing to thrive in marine environments to this day. Fossilized herring have been found in the western United States, particularly where the states of Colorado, Utah, and Nevada meet.

In Vietnam, fishermen often give unique names to the herring species they catch. Two common types are the 'Ve' herring and the 'Lam' herring. The Ve herring has a slim body, with many white-greenish scales, tender white flesh, and a fatty taste but with many bones. The Lam herring has a rounder body, fewer scales, more meat, but its flesh is redder and less flavorful than the Ve variety.