When Pesticides Aren’t an Option, Weaver Ants Are

A groundbreaking new study by Aarhus University reveals that ants can replace toxic pesticides as a greener and cheaper agricultural alternative. Published on August 31 in the British Ecological Society’s “Journal of Applied Ecology,” the paper shows ants control pests on numerous crops, such as cocoa, citrus, and cedar, just as well—and more cheaply—than chemicals. Dr. Joachim Offenberg, an ecologist from Aarhus University who has studied ants for over 20 years, was the the lead scientist on the investigation, which tested 50 pest species on nine crops across eight countries around the globe.  

As the world population continues to increase and resources become scarce, farmers need more sustainable pest control measures. The majority of the studies in Offenberg’s evaluation were on weaver ants, also referred to as Oecophylla, a tropical genus that thrive in trees and weave ball-shaped nests from the leaves. Since weaver ants live near the flowers and fruit of their host trees’ canopy, they make excellent pest controllers in tropical orchards because they protect the most important part of the plant.


Weaver Ants. Courtesy of Wikimedia Commons

And the implementation is easy: farmers simply collect ant nests, hang them in plastic bags on their tree crops and feed them a sugar-based syrup while they create their new nests. Once the colony is constructed, the farmers then attach the trees that are part of the colony with aerial ‘ant walkways’ made from string or long-stemmed vines called lianas. The ants need little maintenance, save for some water during the dry season and pruning of the trees to prevent quarreling between colonies.

Crops like mango and cashew are especially receptive to the weaver ant process in place of pesticide. A three-year study in Australia found cashew yields were 49 percent higher in plots protected with ants versus plots protected by chemicals. The quality of the nut was also higher—70 percent, to be exact—with ants compared to synthetic pesticides. “Although these are rare cases where the ants were superior to chemicals, many studies show that ants are just as efficient as chemical controls. And of course ant technology is much cheaper than chemical pest control,” Offenberg said.

Comparable studies done on Australian mango crops revealed ants were capable of producing similar yields to those from chemical controls, but the fruit quality was higher and cheaper, creating a 73 percent increase in net income.

Offenberg thinks that with more training for farmers, ants could potentially be used in more temperate climates and forestry.

“Weaver ants need a canopy for their nests, so they are limited to plantations and forestry in the tropics. But ground-living ants can be used in annual crops such as maize and sugarcane. European wood ants are renowned for controlling pests in forestry, and new projects are trying to use wood ants to control winter moths in apple orchards. Ants could even be used to fight plant pathogens because they produce antibiotics to combat diseases in their dense societies,” he adds.

Because ants live on every continent except Antarctica, they can be used almost anywhere for agricultural purposes. Some estimates suggest the mass of all ants on Earth exceeds that of humans. Ants eat other insects, and most ant species burrow in soil, though some tropical species nest in trees and bushes. It is their efficiency, however, that makes them great pest controllers.

Offenberg said, “Ants are great hunters and they work cooperatively. When an ant finds its prey, it uses pheromones to summon help from other ants in the nest. By working together, they can subdue even large pests.”


Would you rather eat something that was protected by ants instead of chemicals?




Zara Zhi
Zara Zhi
Zara is a freelance writer and filmmaker who has worked for numerous magazines and news sites. When not coming up with puns or writing screenplays, she enjoys having blind children read to her and donating plasma TVs. Follow her on Twitter: @zarazhi