Air Pollution's Hidden Impact on Insect Behavior and Ecology

Air pollution is a widespread issue affecting millions of people around the world, causing disastrous effects. But we humans are not the only ones to suffer from unclean air. In the last decade, a growing body of research has started to demonstrate how air pollutants disrupt many aspects of insects’ lives too— pollination, behavior toward each other, and even sex.

The main air pollutants that scientists are most concerned about in insects are nitrogen oxides and ozone—both naturally present in the atmosphere and increasing due to human activities. Those gases can react with and break down some of the compounds that insects use to communicate with each other, or that guide the communication between insects and plants.

Science is revealing that air pollutants can affect insects and plants even at levels considered safe for humans. While this field of research is still at its early stages, “the more we find out, the more we see that there's really big potential impacts on these ecological communities,” says Jeffrey Riffell, sensory ecologist at the University of Washington.

Pollution can hamper the social life of one of the most social animals of all: ants. Ozone gas can turn members of the same colony against each other, according to a new study published February in the journal PNAS.

Smell plays a major role in ants' world. Each colony usually has its own signature odor, and when a creature with an unfamiliar smell enters the colony, ants usually turn against it. Ozone, however, can slightly change that odor by interacting with hydrocarbons, which play a role in the colony's scent, on ants’ bodies.

The team reared five different ant species in the lab for months, growing artificial colonies with hundreds of workers. Then, they picked four workers who lived in the same colony and put them in a box with sugar water. After four days, they would take one of the ants out and expose it to increased levels of ozone, similar to those you would measure outside on a polluted day, for around 20 minutes, which is the amount of time an ant would usually spend outside of the colony looking for food.

Scientists filmed how the ants interacted afterward. In four out of five species, if an ant had been exposed to ozone, the nestmates reacted aggressively when it returned.

While an ant entering a foreign colony would be usually killed, the attacks toward the nestmates in the experiment were usually not deadly. Still, “if every time when you come back, you become attacked and have to deal with it for five or 10 minutes,” that might be enough to “mess up the whole structure of the colony,” says Markus Knaden, an animal behavior scientist at the Max Planck Institute for Chemical Ecology and study co-author.

The team also found out that in the case of the clonal raider ant, the only species where the nestmates didn’t attack each other in reaction to ozone, the pollutant affected the insects in another, subtle way. This species use odors to define tasks in the colony. Larvae, for example, are known to ask for food using a partially chemically based communication, says Knaden. But in an experiment involving increased levels of ozone, the ant stopped taking care of the larvae —possibly because that communication channel got somehow disrupted.

“The impact is relatively minor on the pheromones that these ants are producing, but it's having a really big behavioral impact,” says Riffell, who wasn’t involved in the study.

Knaden and his team believe their results can apply to many other species of ants, especially those that are active during the day, when ozone levels are higher, and to species that doesn’t build nests underground, but for example on trees, where they are more exposed to air pollutants.

Other studies on pollinators such as hawkmoths and bumblebees shows how air pollutants can mess up the signals emitted by flowers to attract insects—making it more difficult for the critters to find the flowers and so feeding and pollinating. Air pollutants break down chemical compounds that form the basis of their communication channel, despite the fact that “flowers and their pollinators have co-evolved over millions of millions of years,” says Knaden.

Early-stage research is also showing that exposure to high levels of ozone can cause physiological stress in some insects—possibly leading to alterations in their behavior. Ozone has also been shown to possibly affect bumblebees’ ability to learn. Some insects’ antenna also seems to become less sensitive after exposure to ozone.

Particulate matter can play a role too, covering insects’ antennae, possibly reducing their sensitivity and therefore their ability to sense chemicals.

“It has these all sorts of downstream impacts that are not only impacting their ability to perceive the world, but also can be affecting their physiology as well,” says Riffell.

The effects of air pollutants go further, affecting the sex lives of insects too. Just like in a dramatic romance novel, when the sex pheromones—which play a role in attraction and mating—gets broken down by air pollutants, the insects are unable to find mates.

In two studies published in 2023 and 2024 in Nature Communication, Knaden and his team investigated such effects on drosophilid flies. In these insects, males usually attract females using sex pheromones. But as air pollutants caused the pheromones to deteriorate, the team showed, males became less attractive in the eyes of the females. Deteriorated pheromones also led males to court other males, since they didn’t smell like males anymore. Individuals from different species even began to breed with each other—as females could not distinguish between males of different species anymore.

Knaden hypothesizes that the effects of air pollution on the sex lives of insects might turn out to be the most dramatic ones. Pollutants are probably able to alter and disrupt the function of sex pheromones of most insect species through chemical interactions, says Knaden. “I think that is the very dramatic thing that might happen that no one has really taken a look at.”

In the case of feeding, research suggested that some insects might be able to learn and adapt to recognize and follow the flowers’ smell altered by pollutants. But when it comes to sex, insects can’t learn to recognize and go after differently scented sex pheromones than those they evolved to, says Knaden.

With many questions unanswered, only the effects on a few species of insects have been studied so far. Riffell says that research should move out of the lab too, to investigate directly in the field the effects these pollutants are having on insects. Another step is also try to understand how air pollution impact insects differently around the world.

Some insects don’t see these deleterious effects of pollution. “Agricultural pests, such as aphids, are less impacted, and some even increase under air pollution by taking advantage of lower defenses in pollution-stressed plants,” says James Ryalls, ecologist at the University of Reading.

But on a broader scale, all over the world, insects are declining due to different threats such as loss of habitat and pesticides. Air pollution is one more threat to population numbers. The consequences might even spill over into the human realm, experts say.

“There’s now enough evidence to show that [air pollution] really modifies, say, pollination, and we really require pollinators for our food security, for our crop production, etcetera,” says Riffell. “I think what we need to do now is start to be able to forecast how these pollutants are potentially shaping our ability to have food in the grocery store.”