Illustration by Adelaide Tyrol
Despite the late spring this year, the wine-colored spikes of peony flowers have now pushed their way back into the aboveground world. These spikes will soon be covered with swelling green knobs of buds. And covered with ants.
It can be a shock for gardeners to find dozens of ants crawling around on one of our most beloved spring garden flowers. Far from causing trouble or harming the flowers, however, these ants are an essential part of the peony’s flowering: no ants, no flowers.
The ants are drawn to the tightly furled peony flowers by a sweet nectar exuded from the waxy, red-rimmed bud scales. In return for this high-energy food, the nectar-seeking ants gently probe the clenched petals, loosening the folds and helping the flowers open. Some gardeners say the ants only encourage and hasten a process that would otherwise happen on its own, while others insist that, without the ants eating away the waxy scales and traipsing between the petals, the buds would not be able to open at all.
In either case, the ants also guard the peonies against harmful insect pests that would otherwise damage the plants and diminish the ants’ proprietary nectar supplies, leaving gardeners with nothing more than chewed, unopened buds. The moral of the story: set aside the pesticide; far from being a problem, these ants are part of the solution.
Ants and peonies together form a mutualism, a type of symbiotic relationship that is beneficial and often essential to both of the parties involved. Mutualisms have evolved between many plants and animals over thousands of years of living together in the same habitat, leading to species with specialized and co-dependent interactions. With these mutualisms driving the inner workings of many natural systems, even the most insubstantial-seeming species such as ants – which we often mistakenly label as merely “pests” – play a key role in maintaining the natural balance.
Ants are social insects, working together to build intricate colonies, transport huge volumes of material in orderly columns, and divide tasks among designated workers. But what is equally interesting about ants is how frequently they form symbiotic relationships with other species.
Some of North America’s ant species form mutualisms with other insects. Honeypot ants, which live in desert and semi-desert regions as well as here in New England, herd aphids and other scale insects, bringing them under cover or into their own anthills at any sign of threat from predators. In our neck of the woods, the ants actually take their aphid cattle underground in the fall to protect them from the cold, carrying them back up to the surface when plants grow again in the spring.
The ants go to all this trouble because the aphids, unable to digest all of the sugar in the sap that they suck from leaves, excrete it as a sweet “honey dew” from their anuses. The ants expertly milk them for this honeydew by stoking the aphids’ backs with their antennae. The honeydew provides a constant supply of food for the ants, and the ants provide protection and security for the aphids.
Yet another example of ants acting mutually with flowers takes place in the springtime, as our woods are bursting with wildflowers. Bloodroot, violets, trillium, hepatica, and other spring wild flowers depend on the eating habits of several local ant species to ensure their propagation. Each tiny seed from these plants comes equipped with a lipid-rich packet in the membrane of the outer seed coat called an eliasome, which is the perfect fatty food source for an ant. Biologists have been hard-pressed to find any important physiological use of the eliasome’s contents by the plants themselves. Instead, they believe that the eliasomes have evolved specifically as a food source to attract ants.
Look carefully and you may be able to see ants trucking these self-contained sacs of food – seed still conveniently attached – across the forest floor and hiding them in underground caches. Once the ant has removed and eaten the stored fats, the fertile seed is discarded, having been successfully dispersed to a new habitat and buried carefully in the ground, ready to sprout the following spring. The wildflowers’ mutualism with ants is crucial for seed dispersal throughout the forest.
Creeping, scurrying, and winding their way across the forest and garden floors, our local ants often go unnoticed and un-acclaimed. But in many ways, these small workers are tying ecosystems together, connecting insects to plants, and creating delicately balanced mutual relationships of extreme importance to the workings of the whole system. Ants even form a mutual relationship of sorts with us humans – cleaning up our favorite picnic spots so that the ground will be clean and ready the next time we happen by. All in exchange for a few free crumbs.
Norah Lake is an intern at Northern Woodlands magazine in Corinth, Vermont.