To be able to witness a swarm, whether it involves a megapod of dolphins, a giant flock of starlings, swarming red crabs or cicadas, and watch it move with elegance and magic, is an electric feeling which is hard to explain but easy to understand. Nature has her designs
On a scuba diving excursion, quite by chance I found myself right in the middle of a shoal of a few thousand bait-fish. Thinking that I was a danger to them they grouped and moved around me twisting and turning, forming a silvery wall that seemed to have a life of its own. Within a few moves they had gone above, around and under me, and left me confused and disoriented. This was my first experience of a ‘swarm’, and it left me with a truly unforgettable experience.
Typically, when we think of swarms, we think of insects like bees or locust, but giant swarms exist in birds, bats, crabs, ants and fish too. The name might change but the behaviour of a flock of birds and a school of fish is very similar. While swarming is very impressive to look at, it’s what is happening within a swarm which is fascinating. There almost seems to be a single brain instead of individual decisions that controls a swarm.
In 1996, a cicada population classified as Brood II was born under the ground in the eastern half of the United States. There are several cicada species across the world, but what makes Brood II, a periodical cicada, special is that its population only matures every 17 years. From the time of their birth to their maturity, millions of cicadas wait underground — a 17-year wait which culminates with a mass emergence. Multiple million cicadas crawl their way up into the light and then spend the remaining few weeks of their lives mating and laying their eggs in tree branches. The adults die and the newborns dig their way into the ground and settle for their waiting period.
This year marks the 17th year and the cicada nymphs have starting crawling out in huge numbers. A large group of cicadas in mating mode can generate a noise level of 100 decibels. This year 30 billion cicadas are expected to emerge. The counting is actually done not by counting the cicadas since they all look alike and might be moving around too much, but by counting their escape holes per metre square. With billions expected it is astounding to think of how they coordinate their emergence over a 17-year period.
A biological clock or perhaps a complex earth cycle triggers a particular hormone in each cicada around the same time and sends them out on a mission to breed. Scientists and researchers are busy trying to make the most of this event, for the next chance they’ll get will be in 2030.
One of the most impressive swarms to witness is that of free-tailed bats. Millions of bats migrate to Texas from lower altitudes in summer and inhabit a select few caves, known as Guano Caves. The population of bats has been estimated to be around 104 million. Brazilian free-tailed bats appear on the wing several minutes before dark. The famous bat flights at Carlsbad Caverns are made up almost entirely of this species. With the largest cave holding over 30 million bats, it was believed that in these over-crowded caves, mother bats made no attempt to locate their own young but would nurse any baby bat they encountered. Today we know that this is not true and mother bats can locate their own young within this gigantic swarm. Super-sized swarms like the bats seem to form an organic and shape-shifting dark cloud.
Within this cloud and its thousands and millions of individuals there is a constant flow of complex information being exchanged. Shoals of fish and alkali flies use the swarm as a way to confuse and evade predators —bending and twisting and sometimes forming rolling waves. The predators get confused and can’t pick on any one individual to target.
Fire ants take swarming to the next level. As they march through, they create bridges and even rafts of themselves to cross any obstacles they may come across. With the power of sheer numbers, fire ants are formidable and even large animals will make a special effort to not cross their path.
Scientists have long since been trying to replicate and decode the behaviour and the strength of a swarm and have now made some discoveries. They studied the ‘hero’ of all swarming creatures, the common starling, a passerine bird which can create a flock of approximately a million individuals. Watching a starling flock on the move when under threat by a predatory bird or especially when they are ready to roost, is like witnessing the greatest aerial acrobatic show that nature has to offer. Changing direction, suddenly dropping height, banking, spreading out and coming together in complete unison, and that too without colliding with one another, the starlings had scientists guessing for quite a while.
A European project which involves biologists, physicists and even economists called Starlings in Flight, has unravelled the mystery behind this ‘thinking’ swarm. Till now, computer models built to simulate swarms were engineered around the assumption that a single bird keeps track of all birds within a certain distance from itself. While this was a plausible theory, what has now been revealed is that individual starlings keep track of exactly seven other starling neighbours, irrespective of their distance from itself.
This discovery has changed the way we have so far looked at the swarming behaviour and has explained why, even in very large flocks, individuals seldom get isolated or disoriented and left behind. Very large flocks of starlings are also incredibly noisy, and towns and cities which fall within their roosting areas have had a real challenge to deal with. While most areas are tolerant, there have been cases of mass culling of starling flocks where roosting trees were incinerated with explosives as the birds had settled in to roost.
Each year, a busy motorway in Taiwan is closed down to allow migrating milkweed butterflies to pass safely. Over one million butterflies cross this 600-metre segment of an elevated expressway every day and, reportedly, at the peak moment, has had around 11,000 butterflies pass each minute.
Earlier, before the protection and awareness had begun, thousands of butterflies would be killed by vehicular traffic as they made their way to their breeding grounds in the north. Thankfully, today they are not only protected but have a festival organised to commemorate and celebrate their annual migration.
To be able to witness a swarm, whether it involves a megapod of dolphins, a giant flock of starlings, swarming red crabs or cicadas, and watch it move with elegance and magic, is an electric feeling hard to explain but easy to understand — for nature has her designs and we are but a small part of that.
(The writer is a wildlife film-maker)