Animal swarms are awe-inspiring, bewildering, mesmerizing...sometimes even hair-raising. There are few events in nature more mystifying. There's just something hypnotic about the way that swarms move in concert, as if each individual within has forsaken its own agency and become part of a whole, like the herring shown here. Observing a swarm from afar can even give the impression of a collective consciousness - that the swarm itself has a mind of its own.
Most animals exhibit swarm behaviour in some form, but it's the world's largest swarms that capture the imagination. (Text: Bryan Nelson)
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1. Mayflies
Adult mayflies typically live for only a day or two; they live fast and go out with a bang. Often all the mayflies within a population will hatch at the same time, blanketing the skies in superswarms. The briefness of their lives requires that they emerge in concert so that they can breed.
Of the roughly 2,500 known species of mayfly, about 630 of them can be found in North America. Since the insects are harmless, without stings or even mouths for biting or eating, mayfly swarms are understandably more welcome than many other insect swarms, even though some swarms are so thick that they can become road hazards.
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2. Springbok
These frolicking antelope (springbok) have been known to form the largest herds ever recorded. It has been estimated that some herds numbered in the tens of millions, and likely spanned for as long as 90 miles.
Unfortunately, hunting, habitat loss and disease have drastically reduced their numbers, so they are not as numerous as they once were. We can only imagine the spectacle of such massive herds dancing across the African grasslands today.
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3. Red-billed quelea
Red-billed quelea are the world's most abundant wild bird species, with an estimated population of 1.5 billion breeding pairs. When they flock, they can act almost like locusts, causing widespread damage to crops.
A film crew from the documentary series Planet Earth filmed the largest flock of quelea ever caught on camera - an almost incomprehensible collective of fluttering feathers. It's enough to make even Alfred Hitchcock squirm.
4. Christmas Island red crabs
Endemic to the remote Christmas Island in the Indian Ocean, the red crabs embark on a seasonal migration that is truly one of nature's grandest spectacles. Every year during breeding season they transform the island into a vast moving red carpet as they scurry to the ocean to lay their eggs.
Anywhere from 40 million to 120 million crabs are believed to blanket the island, and during peak migration roads must often be closed. Here is a video from Parks Australia documenting the annual event that has to be seen to be believed.
Related Link: Secret to red crabs' epic migration discovered
5. Herring
Many kinds of fish congregate into shoals, but few rival the mega-shoals of herring, which have been called the world's biggest animal groupings. The fish shoal to avoid predation or when it's time to breed. As a shoal grows in size, more and more fish tend to gravitate toward it until it reaches a mammoth size. Some shoals have been recorded to contain tens of millions of herring, covering dozens of square kilometres.
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6. Locusts
Plagues of locusts are the stuff of nightmares. The largest swarms have been known to number in the trillions, and can consume whole country sides in mere hours.
One of the largest recorded locust plagues in North American history, Albert's swarm, occurred in 1875. It was named after physician Albert Child, who measured the size of the swarm to be 198,000 square miles - roughly the size of California. The swarm may have consisted of as many as 12.5 trillion insects, which, if true, would make it the largest concentration of animals ever recorded.
7. Argentine ants
If you thought that humans had principal jurisdiction over the Earth, you may want to think again. It turns out that ants may have a more credible claim to world domination. In fact, scientists have recently discovered a single mega-colony of Argentine ants with a home range that nearly spans the globe, occupying lands as far reaching as Europe, the Americas and Japan.
The largest unbroken collective of this elephantine mega colony stretches over 3,700 miles along the Mediterranean coast.
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8. Krill
Gatherings of krill are among the largest swarms of creatures on Earth. In fact, some of their swarms are so massive that scientists have taken to labelling them superswarms.
These diminutive crustaceans can be found in all the world's oceans, but their biggest superswarms are located in Antarctic seas, often stretching for tens of kilometres and measuring 30 meters deep.
Though individual krill are tiny, their superswarms are dense enough to be a principal food source for the world's largest animals: baleen whales.
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9. Mosquitoes
You might think that the best time to visit the chilly Arctic tundra would be when the weather is nicest, during the spring and summer. But one look at this terrifying video is sure to change your mind on that front.
The video depicts a scientist virtually engulfed in a massive swarm of bloodthirsty mosquitoes. Swarms of this size can be relatively commonplace when the weather warms and the permafrost thaws, and the mosquitoes emerge from their eggs en masse.
Related Link: 10 things you didn't know about mosquitoes
Top image: A flock of auklets exhibiting swarm behaviour. Credit: D. Dibenski/Wikimedia Commons.
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