Party kings: Which animals on Earth create the biggest gatherings?

The history of our planet spans over 4.5 billion years, during which it has become home to an incredible number of species. Across the globe, animals frequently gather in groups that would make a concert in the largest venue seem like a children's party, as noted by IFLScience.

According to researchers, animals may have several reasons for forming mass gatherings, including:

• the need to run;
• to feed;
• to reproduce.

In reality, such gatherings can be crucial for the survival of a species, but there are also examples where they have had a destructive impact on humans and the environment. Which species on Earth can truly create the largest crowd?

Researchers point out that one of the most massive animal migrations occurs annually in the Serengeti, where over 2 million wildebeests embark on a journey in search of green grass during the rains. This movement of wildebeests is also known as the "Great Migration" and is one of the largest events in Africa's wildlife. According to scientists, this migration is vital for the animals to remain fed and to care for their young, which is no easy task amid lions and hyenas.

The quest for food means that other herbivores, such as antelopes and zebras, join them, but as they traverse the landscape and its waters, more predators like crocodiles enter the herd. As the seasons change, the shifting environmental conditions eventually lead them back to where their migration began, continuing year after year in a clockwise pattern.

Scientists believe this event might represent the largest congregation of animals on the planet. However, they also suggest it may not be the most substantial. Even among mammals, the largest herd is led by the Brazilian free-tailed bats (Tadarida brasiliensis), which hide in caves in colonies of up to 15 million.

When it comes to birds, starlings may take the lead, as they can gather in flocks numbering in the millions, but scientists note that Antarctic penguins (Pygoscelis antarctica) actually form colonies of around 2 million individuals.

2 million may seem like a large number, but the congregation increases tenfold when it comes to albatrosses migrating from New Zealand to Alaska. Yet, even this is not the most populous gathering — researchers highlight that pigeons flock together in groups of several million. These birds are considered the most numerous on the planet, with around 1.5 billion, making their migration an extraordinary spectacle.

And what about the ocean? From October to January, red crabs (Gecarcoidea natalis) emerge from their forest homes and head towards the ocean. Up to 50 million crabs will race across the island, which has had to construct special crab highways and bridges to keep them safe from vehicles. At the same time, herring can accumulate in colonies of up to 4 billion individuals.

Another oceanic contender is krill: these organisms often form massive swarms or schools in the Southern Ocean — their concentrations can stretch for 20 kilometers and contain over a million tons of krill.

When it comes to insects, the main contenders are ants. These small eusocial insects live in vast colonies across the globe, but one species seems to take the crown: the Argentine ant (Linepithema humile). Studies show that the largest known "supercolony" of these ants is so extensive that it spans three countries: Italy, France, and Spain.