Home » Gardening Information » Gardening for Wildlife
Ants—The Astonishing Intimacy Between Ants & Plants
Plants & Gardens News Volume 14, Number 1 | Spring 1999
by Janet Marinelli
Ants are the Rodney Dangerfields of the insect world—they don't get no respect. If they aren't being stomped on they're being doused with toxic pesticides. Two recent animated films, Antz and A Bug's Life, suggest that ants are finally getting their due, at least in Tinseltown. However, even Hollywood's vision of antdom says less about the insects than about predilections of the species known as Homo sapiens.
Dreamworks' Antz, for example, is the story of Z-4195, an angst-ridden worker (with the voice of Woody Allen) besotted with the beautiful princess Bala (Sharon Stone), the pampered daughter of the colony's queen. Bala doesn't give him the time of day ... until a remarkable turn of events transforms Z from an ordinary drone into an unlikely hero, leading a revolution that every red-blooded American will recognize as a celebration of individuality in the face of stifling societal expectations.
It may be stretching reality to depict ants as freethinking role models for peer-pressured adolescents. But they can certainly teach us gardeners a thing or two.
Society Types
If we humans represent the summit of vertebrate evolution, then ants represent the pinnacle of insect evolution. Like us, they lead an advanced social life. In ant colonies, adults take care of the younger generation, and there is a division of labor, with workers who forage and hunt and kings and queens who, basically, reproduce. In the words of Bert Hölldobler and E.O. Wilson, authors of the Pulitzer Prize-winning tome The Ants, these spunky creatures "run much of the terrestrial world." In the woodlands of the Northeast, for example, they move about the same amount of soil as earthworms, and in tropical forests they even surpass earthworms as earthmovers. Many ants are also adept at pastoral pursuits, literally herding plant-sucking insects like aphids and feeding on their sugary excrement, just as we humans tend cows for their milk.
What's more, ants are the world's great gardeners. In fact, ants and plants have some of the most bizarre and elaborate relationships found in nature -- relationships that make the behavior of even the most passionate orchid collector look like puppy love.
Consider the alliance between ants and Australian acacia trees. The plants attract ants by producing nectar in "extrafloral nectaries" found at the base of each leaf. The plants also literally house the ants, sheltering them in their hollow thorns. The ants return the favor by protecting the plants, providing a live-in police force on constant patrol, driving off herbivorous insects that would otherwise dine on acacia. The ants even protect the plants from competing vegetation, trimming away errant leaves and stems that encroach upon with their acacia abodes.
Probably the most byzantine relationship between ants and plants is the phenomenon known as the "ant garden," a group of tropical epiphytes (plants that grow on other plants) assembled by the industrious insects. These horticultural creations look a lot like Chia pets—round green heads with hairlike leaves popping out. To build them, ants bring the seeds of the plants into their carton-like nests. As the seeds germinate and grow, nourished by composting detritus brought back to the nests by workers, the plants' roots intertwine, becoming an integral part of the colony's domicile. When the plants mature, the ants also get a built-in pantry of fruit pulp, as well as round-the-clock libations from the extrafloral nectaries.
Talking Trash
Ant gardens are the Versailles and Sissinghursts of antscape design. But ants are great dirt gardeners, too.
In recent years scientists have discovered that ants are among the planet's most important seed collectors and dispersers. Plants dispersed by ants have been found in diverse habitats on every continent except Antarctica, and are especially common in dry shrub vegetation in Australia and South Africa and in the moist woodlands of eastern North America. According to detailed studies of forests in West Virginia and New York, the seeds of one-third of the herbaceous wildflowers are dispersed by ants, among them beauties such as bloodroot, Dutchman's breeches, trilliums, and trout lilies. According to Rutgers University biologist Steven Handel, ants have often been observed carrying seeds three to six feet, but trips of 200 feet or more are not unheard of. Ants carry seed away from competing parent plants, where they have the best chance to germinate and get off to a good start. Another bonus of seed disperal by ants is the expansion of a plant's range.
In return for the moving service, the ants get a meal out of the deal. While seeds dispersed by the wind are designed to be easily airborne with, say, plumes or parachute-like appendages to catch the breeze, and those dispersed by birds or mammals come wrapped in fleshy fruits, seeds dispersed by ants have an outer tissue, called an elaiosome, that's as enticing to the critters as an open bag of potato chips. Fleshy in consistency, whitish in color, full of proteins, sugars, and other goodies, elaiosomes are often large and come in myriad shapes, depending on the species. There are eliaosomes that look like little hoola hoops, pocket hankies, skullcaps, elegant draperies, girdles, and shriveled fingers. Some sheathe the entire seed like tiny condoms. Eliaosomes may have different shapes but they all have the identical effect: Any ants in the vicinity suddenly act as if they're in seventh heaven, grasping the seed excitedly and marching straight to their nest, where the workers chew the eliaosome into pieces and feed it to the larvae (infant ants).
After using the eliaosome as baby food, the ants typically discard the rest of the seed unharmed. Ant colonies, like human societies, have a tendency to accumulate trash. But unlike too many human communities, ant colonies put their detritus to good use. Seeds are dumped in the colony compost heap, along with the remains of prey, fecal material, ant corpses, and in the words of Steven Handel, "a host of other items (many of no apparent use)"—a ready-made cache of rich organic matter that nourishes seedlings through their delicate early stages. Nest building also renders the soil crumbly and well-aerated and improves water-holding capacity, making ant nests ideal plant nurseries.
One ant and plant expert compared the success rates of ant-sown versus randomly sown seeds of a violet species found in the rolling chalk hills between London and England's south coast. He offered several hundred seeds to foraging ants, who immediately took them to their nests. He then planted an identical number of seeds by hand, at random. The violets that emerged from the ant nests were lusher and healthier than those that grew from the hand-planted sites, and there were more of them. After three years, only plants that had sprouted from ant nests survived.
The intimacy between ants and plants dates back to the days of the dinosaurs. But this ancient relationship is in trouble. In the northeastern forests, for example, roads and other developments are carving up natural areas, preventing ants from moving the seeds of wildflowers like Dutchman's breeches from the fragmented patches of virgin forest to the second- and third-growth forests that have become so common in the region over the past hundred years. If these wildflowers are ever again to grace the woodland floors of New England's returning forests in spring, we humans will have to act like ants and plant them there.
Brooklyn Botanic Garden Director of Publishing Janet Marinelli is editor of BBG's renowned series of quarterly gardening handbooks and the author of Your Natural Home and The Naturally Elegant Home. Janet is a champion of the gardener's role in the preservation of the planet, a philosophy that informs her P&G News column, "Down to Earth." It's a philosophy that also serves as the bedrock for her latest book, Stalking the Wild Amaranth: Gardening in the Age of Extinction. In Stalking the Wild Amaranth, Janet tells of her quest for a landscape art that protects disappearing species, both flora and fauna. It's a gardening journey marked by humor—ecologically sensitive gardening needn't be a dreary affair, Janet insists. "We can do our part," she says, "and still have flair and fun."