THE STEINHART AQUARIUM - Gulf of Guinea Science ...

gardening ants, number about 200 species,
all in the tribe Attini, and are found only in
the New World, in every mainland country
except Canada and Chile. Most leafcutter ant
species are native to tropical Central and South
America, though a few species occur in the
southwestern United States.
Atta cephalotes ranges from southern Mexico to
Costa Rica and south to northern Argentina.
Habitat: Colonies are found throughout
the tropical rain forest, tropical deciduous
forest, and tropical scrub forest. Nests are
underground to a depth of 6 m. Some have
up to 3000 chambers, hundreds of “gardens,”
and can cover an area up to an acre. Crescentshaped
mounds at the entrance of the nests
contain as much as 350 m 3 of soil.
Appearance: Rust colored with lighter colored
legs, members of the genus Atta are among the
largest, most socially complex leafcutters. The
huge queen is up to 1.5 cm in length, an egglaying
machine capable of building a colony
of several million individuals. Atta cephalotes
is noted for its especially large head (hence the
name). Workers take many forms and sizes,
from large soldiers and major workers with
their impressive mandibles to the smallest
workers, sized to move easily through the
narrow galleries of fungal gardens. A soldier
may be 10 times longer and weigh several
hundred times more than the smallest worker.
The abdomen has a stinger, but it is not used.
Diet: Leafcutter ants are true gardeners.
They grow their own food by cutting leaves,
mostly during the evening and nighttime, and
carrying them back to the nest, where smaller
workers then process them further and take
them to underground “garden” chambers. All
along the way, the leaves are fertilized by their
handlers with anal secretions. Fungi then grow
on the decaying vegetation, and the ants feed
exclusively on the fungus, not the leaves. Each
ant species grows a specific fungus.
Reproduction & Development: Atta cephalotes
swarm in mating flights at the onset of the rainy
season. The queen mates with multiple males.
The founding female has a pocket in her mouth
cavity for storage of fungus spores to start her
new nest. After she digs the first chamber for
the garden, she deposits the spores, gathers
appropriate leaves, and begins laying about
California Academy of Sciences
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1000 eggs each day. The first group of workers
to develop takes over for the queen in caring
for eggs, larvae, and pupae. The queen has
only one job then—to lay the eggs that will
build the colony.
Mortality/Longevity: Queen lives up to 10
years on average, but some have lived up to
14 years.
Remarks: Fungus and ants are mutually
dependent for survival. Obviously, the fungus
provides the ants with food, but equally
important, the fungus receives a warm, moist
home and is supplied with fresh, fertilized
nutrients. The ant colony also remorselessly
rids the colony of any competing fungal strains.
Many ants make noises while they work,
generating the sound by rasping a file-like
widget on one segment of the gaster (the
enlarged part of the abdomen) against a
specialized rough spot on a neighboring
segment. The ants pick up the vibrations, called
stridulations, with sensors on their knees.
Leafcutter ants are able to set up vibrations
in their mandibles that helps the ants cut
smoothly through leaves. These workers also
seem to communicate via stridulations with a
smaller worker caste that accompanies them
on harvesting missions. The vibrations signal
the small ants to climb onto the leaf for the
ride home. These hitchhiking minor workers
protect the leaf carriers from phorid flies that
try to inject an egg in the braincase or gaster.
If the fly is successful, its larvae parasitize the
ant, ultimately killing its victim by digesting
its body tissues, finishing with the brain and
leaving a headless corpse!
Leafcutter ants are responsible for destroying
more vegetation than any other group of
animals: they inflict more than a billion dollars
in crop damage yearly. A large colony harvests
the same amount of plant material that a cow
consumes in a single day. Some leafcutter
species, though not Atta cephalotes, compete
with cattle for grass and harvested foodstuffs
stored by humans, such as cereal grains, flour,
dried beans, and cattle meal. Large colonies of
leafcutter ants also undermine the foundations
of buildings, causing structural damage.
Leafcutters have their benevolent side as well.
Atta species, like most insects, are a good source
of protein; they are eaten by people in parts of