It is quite a spectacle when animals come together in inconceivable numbers: sometimes in the millions, billions, and even trillions. When swarms gather, a kind of super-organism is created in which individual intelligence is superseded by a collective consciousness that shares information and moves with a single purpose for the benefit of all. This behavior applies to a number of creatures that form these great gatherings for a variety of reasons: to breed, migrate, find food, and even to protect themselves.

Using high-speed camera techniques, The Gathering Swarms captures these world-wide displays and explains why they occur. The documentary airs tonight, May 21 at 8 p.m. (ET) on PBS (check local listings). After the broadcast, the episode will be available for online streaming at

The Gathering Swarms provides many examples of swarm intelligence such as what prompts emperor penguins to start huddling. As the only creatures on earth to breed in the Antarctic winter, their survival, as well as those of their chicks, is put in jeopardy when the temperature falls to 40 below. So, instinctively, emperor penguins all converge on the same central point and begin to form a huddle. As those on the outside take the brunt of the cold, those on the inside take tiny steps that move the huddle in waves. The pack continues to shift and rotate from the center, so no one is left permanently in the cold. The formation often breaks down when those on the inside overheat, at which point the coldest penguins, which were on the outside, form a new center as the other members of the colony huddle around them.

Bees create swarms when they are house hunting. A scout bee is sent out to find a new cavity large enough to house the whole hive. Once she has measured and inspected the new accommodations, the scout returns to let the swarm know its location using a "waggle dance." An advance party follows her to check it out, hold a "committee meeting," and somehow arrive at a consensus. Then the scouting party signals the entire colony that it's time to move, and tens of thousands of bees take to the air as one to make their way to their new home. The whole process is an example of highly-developed collective decision-making.

Like many birds, fish school together on the principal that it is better to be part of a crowd when finding food or facing predators. Travelling up the coast of South Africa, sardines are part of the greatest fish migration on earth. Their ability to simultaneously move as one relies on a pressure sense that runs along their bodies detecting the movements of their nearest neighbor. This "lateral line" also detects predators like sharks, dolphins and flocks of cape gannets. Although sardines try to fend off attacks by staying deep and keeping the school together, some assaults can break up the super-shoal into smaller, more vulnerable target groups. But they will try to rejoin the master shoal as soon as possible, benefiting once more from the collective intelligence of the swarm.

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