Higher yields and better quality

Most of the studies in Offenberg’s review are on weaver ants (Oecophylla), a tropical species which lives in trees and weaves ball-shaped nests from leaves. Because weaver ants live in their host trees’ canopy, near the flowers and fruit that need protection from pests, they are good pest controllers in tropical orchards.

All farmers need to do is collect ant nests from the wild, hang them in plastic bags among their tree crops and feed them a sugar solution while they build their new nests. Once a colony is established, farmers then connect the trees that are part of the colony with aerial ‘ant walkways’ made from string or lianas.

After that, the ants need little, except for some water in the dry season (which can be provided by hanging old plastic bottles among the trees), pruning trees that belong to different colonies so that the ants do not fight, and avoiding insecticide sprays.

The review shows that crops such as cashew and mango can be exceptionally well protected from pests by weaver ants.

One three-year study in Australia recorded cashew yields 49% higher in plots patrolled by ants compared with those protected by chemicals. Nut quality was higher too, so net income was 71% higher with ants than with chemicals.

Similar studies in Australian mango crops found that ants could produce the same yield as chemical control, but because the ants were cheaper, and fruit quality better, net income from mangoes produced with ant protection was 73% higher.

“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 says.

While ants are not a panacea for pest control, he believes that with more information and training for farmers, ants could be much more widely used in temperate as well as tropical agriculture 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 sugar cane. 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 explains.