The Fabulous Leaftut
One of the most common and unique sights of the Costa Rican rainforest is a trail of Leafcutter ants, an endless parade
of tiny workers carrying leaves three times their size. Even more interesting is what goes on inside the nest, deep under the
ground, where the leaves are processed and fed to a mold-like fungus. Look inside to get a new perspective on these
The world of ants:
The ants (Formicidae) are a complex and fascinating group of insects. Ants are the mostbundant group of insects in
terms of numbers of individuals. One hectare (2.5 acres) of rainforest contains over 9 million ants - almost twice the
population of Costa Rica. They are related to the bees and wasps (Hymenoptera), but of the three groups only ants are
completely social insects. This means that every ant is dependent on the other ants of her colony, her sisters, for survival.
Ants are holometabolous, like butterflies. This means they pass through four life stages - egg, larva, pupa and adult. Ants are
well adapted for life underground since most are almost entirely blind. their world is run by chemical smells and tastes. Ants
release pheromones to alert each other to danger, locate food, and work together to perform colony tasks. Because of this a
colony can function as a single organism - centered around the queen. The queen is the mother of the colony. Her task is to
constantly lay eggs to keep the colony populated. Most colonies only have one queen and will die when she dies, although in
some species (fire ants for example) one colony can have many queens. The largest ant colony ever reported was a species
of Formica ants found in Japan. It contained 306 million workers and over a million queens. Ants are a diverse group of over
8,000 species, who dominate a wide range of habitats including and deserts, frozen tundra and kitchen garbage cans.
The Leafcutter ants:
Leafcutters are some of the most advanced social insects on the
planet. A single colony can number up to 7 million individuals. Their nests are also huge, some can be 30 meters across and
over six meters deep. In Costa Rica there are two main types of Leafeutters - Alta and Acromyrmex. The species we have
here, Alta cephalotes, is the most common. They are easy to spot since a typical nest will have many foraging trails that can
lead up to 100m through the forest, each trail like a multilane highway of ants carrying leaf fragments to the nest. A colony
can harvest as much vegetation as an adult cow everyday. During the year, Leafcutter ants harvest 12-17% of total leaf
production in Costa Rica, each species specializing on up to fifty different types of plants. They can become big agricultural
pests since they attack important crops such as banana, sugar cane and come The ants don't actually eat the leaves,
although they will feed on the plant juices. The ants are gardeners. The leaves are taken underground and used as fertilizer
for their fungus crop, their main source of food.
The Leafcutters are dependent on the fungus for their nutrition, since they are unable to digest the cellulose in
leaves. Inside the anthill the fungus gardens look like large piles of breadcrumbs. The fungus is a specialized species found only
in the company of the Leafcutters. It was identified as Leucocoprinus gongy1ophorus, but this is uncertain since the fungus
has lost the ability to make the reproductive structures usually used to identify fungi. Instead it depends on the ants for
reproduction when a new queen leaves her parent colony, she takes a piece of fungus with her to start a her new garden.
After the workers bring the leaf pieces into the nest, smaller workers process the leaves by chewing them into pulp and
adding digestive secretions from their abdomen. Next, even smaller workers place this pulp into the garden, where the
fungus quickly consumes it. In return, the fungus produces small swellings called gongylidia or kohlrabi (because under a
microscope they resemble this vegetable). These swellings are rich in glycogen, and the ants harvest them to feed
themselves, the larva and the queen.
Within the colony there are
various types of ants, known as castes. They look very different - the soldiers can be up to 100 times the size of the minima.
But the differences are not genetic. Which caste an ant belongs to is determined by the amount of food and certain
chemicals they are fed as larva.
THE QUEEN: The Leafcutter queen is a caste by herself She is the heart of the
colony, the mother of every ant. Leafcutter queens are some of the largest ants in the world and can reach up to two inches
in length. They can
live for up to 20 years and lay millions of eggs each year.
THE SOLDIERS: The soldiers are large ants with proportionally huge heads and powerful
mandibles. They are only found in large colonies and always in low levels. Only one out of every 1000 ants in the colony is a
soldier. But they are fierce fighters. Soldiers will attack almost any foreign animal that crosses the foraging trail or enters the
nest, usually fighting to the death. They also work together to remove debris from the trails and carry heavy food objects.
THE WORKERS: Most of the ants are workers, who collect and process the leaves. The largest
workers cut pieces of leaf and carry them back to the nest, where smaller workers process the leaves and feed the fungus.
Some workers also act as scouts and search out new food sources. They leave scent trails for other workers to follow. A
worker can live for about a year.
THE MINIMA: The minima are the smallest ants who harvest the fungus and feed the larva and
the queen. They can also be seer, on foraging trails riding on the leaves carried by the workers. They clean the leaves and
defend against phorid flies. These tiny parasites attempt to lay their eggs on the leaves, so that the eggs will be taken into
the nest where they will hatch and feed on the ant larva.
THE MALES: Males are produced
only once a year and have no function within the colony. Their only job is to fly away and join mating swarms. Each male will
attempt to mate with a new queen from a different colony and pass on the genes of his sisters. Males die shortly after
The Leafcutter ant colonv reproduces itself once a year typicaliy at the start of the rainy season ( in Costa Rica this is late
May, early June). The queen produces a special brood of nearly 50,000 eggs. 40,000 of these are unfertilized and will become
males, the other 5-10,000 will become new queens.
The whole colony becomes more active to collect extra leaves since the queens and males must eat twice as much as a
normal brood. As larva, the queens and males are lavishly cared for by the minima and grow to a huge size. They live inside
the nest for several weeks, gaining strength and waiting for the right moment.
The ants use weather cues to synchronize the release of the reproductives. After a large rainstorm, queens and males
from many colonies will fly high in the air and meet in huge mating swarms. A male will mate once and die soon after, while a
queen will mate several times and collect over 300 million sperm which she will s ' tore to use during her lifetime. After her
nuptial flight, a new queen rips off her wings and burrows into the soil, never to return to the surface. Here she lays her first
eggs and starts fertilizing the fungus garden with her own feces. She lives off her fat stores for the first couple months, until
her first workers are strong enough to leave the nest and find leaves. Most new queens are eaten by predators or starve,
only 1% are able to start successful colonies. If the colony survives its first year, it will grow large enough to produce soldiers.
At this point it is well defended from most predators, its only real dangers are army ants and other Alta colonies that might
invade its territory (and butterfly garden workers with shovels). After three years it will be large enough to produce new
queens and males, and the cycle will continue.
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