The Zoo has one leaf-cutter ant colony in Think Tank and another in the Invertebrates
Exhibit.
The Zoo's leaf-cutter ant colonies give visitors an up-close look at an animal society. While the interactions within the colony are complex, the ant society is an example of nonthinking behavior because the ants don't show flexibility.
Distribution and Habitat
Leaf-cutter ants make up the much of the biomass in the
New World tropics. They support forest ecosystems by keeping
soil turned and aerated and they recycle vegetation and soil
nutrients. There are about 35 different species of leaf-cutter
ants.
A mature colony has between three and eight million ants at any given time. Generally, the population has a queen and her sterile worker daughters. Leaf-cutter ants live in underground nests. The nest is a moist, humid environment good for growing the ant's food, fungus. They are also protected from predators and parasites. Chambers in the nests are used for fungus gardens, egg hatching, and trash disposal. Full-sized colonies can have 3,000 chambers and extend 18 feet (6 m) underground. Trails leading to and from the nest, excavated by the ants, are the transportation routes for leaf collection.
Physical Characteristics
Leaf-cutter ants have a three-part body consisting of a head,
thorax, and abdomen. There are three pairs of legs attached
to the thorax. Reproductive males and females have two sets
of wings. There are different castes of leaf-cutter ants,
each with slightly different sizes and body parts. Soldiers
and all workers are sterile females. The castes are: queen,
winged females, winged males, soldiers, foragers, leaf preparers/degraders,
planters, and caretakers.
At a foraging site, workers hold themselves in place on a leaf with the hooks on the ends of their legs. They slice the leaf horizontally with sharp, saw-toothed mandibles jaws that vibrate 1,000 times per second. Once the leaf is cut, it is lifted overhead, held in place by the mandibles, and carried back to the nest.
Communication
Leaf-cutter ants communicate by releasing biochemical compounds
called pheromones. Each ant receives its colony's distinct
odor shortly after hatching from the egg. Other pheromones
identify each individual ant according to its caste and job.
Life Span
A colony will live ten to 15 years—as long as the single
queen ant lives. Since the queen is the only reproductive
individual in the colony, when she dies the colony begins
to fade.
Diet
Leaf-cutter ants eat the new growth of fungus grown on the
mulch they make from the leaves of many plants. The forager
ants follow pheromone trails to and from the nest as they
collect leaves, and smaller workers then lick the leaves to
remove bacteria or other harmful materials from the leaves.
The leaves are clipped into smaller fragments, fertilized
by defecating and salivating on them, and by chewing, crushing,
and molding leaves into pellets. Planter ants pluck fungus
strands from other fungus gardens and implant them on freshly
prepared leaf mulch. Caretaker ants harvest the fungus and
carry it to nest mates and the queen. The fungus is a clone
of the fungus in the original parental nest; it has been used
by leaf-cutter ants for about 25 million years.
Reproduction
In response to a variety of internal and environmental cues,
the queen in a mature colony will produce another queen and
reproductive males every one or two years. Males die after
mating and the queen will settle to the ground, discard her
wings, and start a new colony.
Husbandry
The colony in Think Tank is tiny. It is housed in man-made,
almost life-sized chambers. Temperature, humidity, and ventilation
are adjusted by the ants and zoo keepers.
