Many farmers see ants as a pesky problem, but in most situations, they can actually reduce pests on a level on par with pesticides. According to a new study, ants can be a cost-effective and eco-friendly way of dealing with pests.

“In general, with proper management, ants can be useful pest controls and increase crop yield over time. Some ant species have similar or higher efficacy than pesticides, at lower costs,” the researchers note.

For as long as there has been agriculture, there have been pests. It makes sense — you have this big field where you plant delicious and nutritious plants; how could you expect freeloaders not to try and take advantage of it? Humans have tried to manage pests in different ways. In recent years, chemical pesticides have become dominant, but there’s a few problems with pesticides. For starters, they can be pretty expensive. They can also be polluting, harmful to pollinators, and there are concerns about human health as well.

Biological pest control is another, very different approach. Basically, you use other animals or plants that can outcompete or prey on pests (or deter them somehow). A simple example would be the use of cats to keep rodent pests at bay, although there are far more examples of insects or plants being used for this purpose.

But what about ants?

Ants and farmers have a complex relationship. The first report on the use of ants as pest control comes from the year 304 AD, when Western Jin dynasty botanist Ji Han wrote that “Jiaozhi people sell ants and their nests attached to twigs looking like thin cotton envelopes[..]. Without such ants, southern citrus fruits will be severely insect-damaged.” Ants keep their colonies safe by eliminating many creatures that would harm crops, but sometimes, they can also have a negative impact.

Ants themselves are rarely pests in agriculture. But some ants are farmers themselves — except they don’t farm crops, they farm aphids. Aphids are common sap-sucking insects, and since they feed by sucking the nutrient-rich liquids out of plants, they can sometimes damage crops. Ants like them because aphids produce honeydew, and ants just love honeydew. So they offer the aphids protection and even transportation in exchange for the honeydew.

For human farmers, these farmer ants can be quite a problem. But overall, the new study reports that the effects of ants are very positive.

The researchers, led by Diego V. Anjos, an entomologist at the Federal University of Uberlândia in Brazil, looked at 52 studies on 17 different crops. The crops included citrus, mango, soya cauliflower, cotton, and sweet potatoes, grown in countries including the US, the UK, Brazil, and Australia. Ants, being the generalist predators they usually are, were efficient at keeping a range of pests at bay. The more diverse the ant population was, the more pests they controlled.

“Overall, the mere presence of ants, regardless of their body size, provided pivotal services for crops,” the researchers note in the study.

While ants did increase the abundance of honeydew-producing pests (aphids) on average, their net effect was strongly positive. In fact, it’s such a positive effect that researchers suggest farmers would be wise to accommodate ants on their crops.

“Therefore, from our results, we encourage practices of shaded crops as a way to naturally promote ants in crop systems. In most cases, ants are low-cost solution. However, in others, it is necessary to move colonies into the crop areas and provide food and/or nests for their survival, as occurs with Oecophylla ants in many locations worldwide,” the researchers add.

Ants also seem to like shaded areas and plant diversity — meaning farmers can implement multiple sustainable practices in one go (planting more diverse crops instead of monoculture and using ants as biological pest control). In shaded areas, ants decreased the abundance of pests by twice as much.

“The presence of other plant species and less intensive tilling in shaded crops reduce the use of pesticides and favor biodiversity preservation, including that of predatory arthropods such as ants,” the study reads.

Biological pest control is usually better for the environment, it’s cheaper, and it’s also better against soil erosion. This study offers one potential avenue through which farmers can reduce costs and tackle pests in a sustainable fashion. We may soon see natural creatures, and not pesticides, protect our crops from those who would damage them.

“The rapid evolution of pesticide resistance and the risks pesticides pose to human and ecosystem health call for sustainable agricultural practices. Biological control of pests is a promising tool in which natural enemies regulate pest densities and reduce damages. Biological control (e.g. providing natural enemies in the ecosystem) not only reduces the use of pesticides and production costs but also helps to maintain local biodiversity. However, the success of biological control depends on many factors, such as the environmental factors and traits of the species involved,” the researchers conclude.

“Some ant species have similar or higher efficacy than pesticides, at lower costs. Moreover, ants can be used with integrated pest management when ants alone are not enough to control the pest.”

The study was published in Proceedings of the Royal Society B.