I've always been fascinated with small worlds. Many living creatures go about their lives almost unnoticed, but it is amazing what you can learn when you take a closer look. Leafcutter ants, perhaps the first farmers, live in a complex society engaged in growing fungus in underground tunnels. Scientists are studying them as a means of monitoring the effects of climate change on biodiversity of species, and to learn new ways to get energy from inedible plant materials.
Although leafcutter ants are mainly a tropical species, Texas can boast of having its very own species of leafcutter, Atta texanis, the Texas Leafcutter ant. Here in the Lost Pines area of South Central Texas, our sandy soil is ideal for construction underground ant tunnels. I often see a leafcutter trail when I go walking with my dog in our woods.The trails are amazingly long. This Leafcutter trail began in the woods, and continued across a nearby seasonal creek bed to the ant mound, extending over 120 feet! The ants had to clear dead pine needles many times larger than their bodies to make the trail.
A closer look at a leafcutter trail usually reveals a line of ants making their way along the trail, each ant carrying a load bigger than its body. Here, in a video taken in Houduras, the photographer followed ants carrying leaves they had cut from a tree back to their nest, which was 1/4 mile away.
Watching them hurrying along the trail towards a chosen plant, and returning to the nest, you might wonder how they know where they are going. E.O. Wilson found that ants leave invisible chemical trails for the others to follow. Forager ants find a suitable plant, and on their way back to the nest, deposit chemical signals along the route, which other ants then begin to follow, leaving more chemical signals as they go. Soon there are many ants coming and going, adding to the chemical trail. It is possible to disrupt the ants by washing away the chemical signal, or diluting it with another chemical signal.
Exactly what the ants are carrying varies with the time of year. In the spring, it might be pieces of newly planted seedlings from your garden. Last year my neighbor Billy, who had hopes of selling onions at the farmer's market, watched in dismay as the leafcutters efficiently cut up and carried off most of his prize onion plants. In the fall, they stock up on American Beautyberries, and their nests acquire a colorful pile of fuscia berries at the entrance.
Later on, in winter, the ants are busy harvesting the bluish berrylike cones of the Eastern Red Cedar trees.
Although Leafcutter ants can strip a plant of all its leaves, and carry them off piece by piece, they don't feed on the leaves themselves. Leafcutters are farmers, who grow a fungus on leaves and other organic matter, and then feed on the fungus itself. The ant cam at the Currie Lab allows you to see ants at work inside a leafcutter ant colony.
Ants in a Leafcutter colony are divided into several highly specialized groups, each performing a different task. There is a queen who lays eggs, workers who gather plant material, soldiers who protect the nest, and tiny minima who groom the fungus. There are even bacteria that live on the ants that produce antibiotics that keep the fungus garden healthy. The worker ants have specialized jaws for cutting off pieces of leaves, and the long legs of a distance runner, which help them carry plant materials back to the nest.
The size of the colonies can be huge. A Texas Leafcutter nest can be 15-20 feet deep, and a colony may last for years, and number over 2 million ants. In one fascinating experiment to determine the structure of a colony of Asian grasscutting ants, scientists poured concrete into an abandoned colony. An unbelievable 10 tons of concrete was required. When the concrete structure was excavated, scientists found a structure that suggested it was designed by an architect, complete with branching tunnels, chimneys that form a ventilation system, fungus growing chambers, and garbage heaps that covered over 500 square feet, and required moving some 40 tons of soil.
According to Texas A&M University scientists, new colonies are formed in the spring, when winged reproductive males and females take flight on clear moonless nights, usually after heavy rains. Following mating, the queen digs a small tunnel, and deposits her eggs. She carries a piece of the fungus from the original colony in her mouth, which is used to start growth of the fungus in the new colony. As new worker ants develop they begin to gather vegetation to feed the fungus in the newly established colony.
Leafcutter ants are mostly found in tropical climates, and only three species are found in the United States, including the Texas Leafcutter ant. How does a tropical species thrive in our cold climate? Scientists think they arrived in Texas some 10,000 years ago at the end of the last ice age. In a recent study, researchers at the University of Texas found that Texas Leafcutters are aided by a cold tolerant fungus that has evolved to survive our Texas winters. The Texas Leafcutters seem to be limited in how far north they can survive by the limits cold temperatures the fungus can tolerate.
University of Texas biologist Ulrich Mueller says that unique ecological conditions make Texas an ideal place for scientists to study the effects of environmental changes on biodiversity. We are the only state that has such a steep east to west precipitation gradient crossing an equally steep north to south temperature gradient. Rainfall amounts range from over 54 inches a year on the Gulf Coast to less than 14 inches a year in West Texas. Yearly temperature averages decrease from south to north from a balmy 73 degrees in South Texas to chilly 57 degrees in the Panhandle. Mueller is interested in what the effects of global warming in the next 10-20 years will be on Texas Leafcutter ant populations, and wonders if they will eventually expand north to Oklahoma and across the Mississippi River.
Scientists at The Currie Lab at the Great Lakes Bioenergy Research Center at the University of Wisconsin-Madison are interested in developing biofuels from non-edible parts of plants to generate cellulostic ethanol, think that understanding how leafcutter ants convert plant materials into create digestible nutrients could lead to alternative energy to replace fossil fuels. Currently, increased use of food crops to produce ethanol is driving up food costs and causing shortages of food plants like corn and casava. Studying leafcutter ants may provide clues on how to use non-edible plant parts instead. Although they prefer my garden seedlings, during drought years, I have even seen leafcutter ants stripping non-food plants like green pine needles from young pine trees to use for cultivating fungus.
Fungus growing ants have been farming for over 50 million years. If they can help us learn how to use non-food parts of plants to make ethanol instead of corn, or prove useful in understanding how biodiversity is affected by climate change, I might just forgive them for reducing my prize purple kohlrabi seedlings to bare stems.