Twenty quadrillion of them, in one enormous family
A team that pulled together nearly 500 separate field surveys in 2022 put the number of ants alive at around twenty quadrillion — a two followed by sixteen zeroes. Weighed dry, that is more than all the world's wild birds and wild mammals added together, though still well short of the total for humans, which is a correction to a much-repeated claim.
Some of them are organised on a scale that is hard to take in. Argentine ants, accidentally shipped around the world from South America, have formed a single supercolony running for thousands of kilometres along the Mediterranean coast, and its members do not fight one another. Ants from that colony, from another in California and from a third in Japan were introduced in a laboratory and treated each other as family — separate populations on separate continents behaving as one COLONY.
At the other end of the scale, a single ant is not much of a thinker. What looks like intelligence is thousands of TINY individuals each following short rules, and the cleverness only exists at the level of the crowd.
Leafcutters are farmers and have been for 50 million years
The lines of ants carrying cut leaf fragments through a rainforest are not taking them home to eat. Leafcutter ants cannot digest leaves at all. They are feeding a fungus, grown in chambers underground, which breaks the leaves down and which the COLONY then eats — an arrangement running for something like fifty million years, making them farmers long before anybody else was.
The farm needs tending. WORKER ants of different sizes handle cutting, carrying, chewing the material into a mulch and weeding out anything growing where it should not, and the smallest ride on the leaf fragments fending off parasitic flies. They also carry antibiotic-producing bacteria on their bodies to keep a specific mould off the crop. Every part of the operation is maintained by an INSECT a few millimetres long.
How a trail finds the short way round
An ant that finds a CRUMB or a grain of SUGAR lays a scent on the way home, and other ants follow it and add scent of their own. Two ants setting off on routes of different lengths will both come back, but the one on the shorter route completes more round trips in the same time, so that path collects scent faster. The longer one evaporates. Nobody compared the routes; the geometry did it.
The method works so well it was borrowed. Ant colony optimisation is a real technique in computing, used on delivery routing and network problems, and it is a fairly direct translation of ants laying and evaporating pheromone. That is the whole basis of the ANT TRAIL you watch MARCH across a kitchen floor.
The rest of the grid is the domestic side: the QUEEN laying every egg, the SOLDIER on guard, the ANTHILL and its MOUND above a maze of TUNNEL and NEST, the EGGS and LARVA being raised below, ANTENNAE reading the way, and six STRONG LEGS able to CARRY many times their owner's weight as the workers FORAGE and the SWARM moves on.