Addict Ants Show That Insects Can Get Hooked on Drugs, Too

How researchers got a non-mammal hooked on drugs for the first time

"Hey guys this sugar is great, but where can we find some morphine?" Nika Lerman / Alamy

The temporary euphoria associated with opioids comes at a steep price: heroin, oxycodone, opium, morphine and other painkilling drugs are some of the highly addictive culprits fueling the drug epidemic that is sweeping America. On average, opioids claim the lives of 78 people in the U.S. each day. Now, in a bid to understand more about substance abuse and how it affects people neurochemically, researchers are turning to some unlikely addicts: Ants.

As it turns out, humans aren’t the only animals who can fall hard for these drugs. Ants love them, too—maybe even more than sugar. In a paper published today in the Journal of Experimental Biology, researchers show for the first time that a social insect can form a drug dependency—a finding that they believe can help us better understand how addiction affects human communities.

“Now that we’ve proven we can addict ants and that the neurochemical pathways are similar to mammals, what’s most exciting to me is the next step,” says Marc Seid, a neuroscientist at the University of Scranton and the study’s senior author. “We can addict individual (ants) and see how that affects the ants’ social network, which is somewhat like humans'.”

When it comes to studying substance abuse, getting humans addicted to drugs isn’t an option. So researchers have long turned to rodents, finding that addicted rats, for example, will chose cocaine over food. But while rats have a relatively similar physiology to people, they are quite distinct socially. They do not form complex, interdependent groups in which other individuals will be affected if someone they know suddenly forms a serious drug habit. Ants do, making them an ideal—if improbable—subject for investigating the cascading effects addiction can have on a society.

First, researchers had to determine if ants could indeed form addictions to drugs. To find out, they set up a classic “sucrose-fading procedure.” This method involves presenting two groups of ants with a bowl of sugar water, and then gradually lowering the concentration of that sweet treat over the course of four days. One of the ant group’s bowls also contained a second treat, which did not diminish in concentration: morphine.

Unlike the ants in the water-only control group, by day five, the ants in the morphine group had returned to their now-sugarless bowl, seemingly to lap up the drug. To see how deep their potential addiction went, the researchers gave both junkie ants and a new group of untrained control ants two options: a sugar-only bowl or a morphine-only bowl. Sixty-five percent of addict ants went for the morphine bowl, while most control ants chose sugar.

“As anyone who’s ever had ants in their kitchen knows, ants really like sugar,” Seid says. “But we showed that [the addict group] foraged much more on morphine than on their natural reward, sugar.”

After the sugar-morphine experiment, the team extracted the insects’ brains to see how their addictions had changed their neurochemistry. They used a technique called high-performance liquid chromatography to detect chemicals in each brain sample. Compared to the control ants, the morphine addicts had significantly higher levels of dopamine, a neurotransmitter associated with the brain’s reward and pleasure centers. Dopamine plays a significant role in addiction in both humans and rodents. 

While past studies showed that Drosophila flies can become addicted to alcohol, those studies always coupled the drug with an extra perk like sugar. The new study, as far as Seid knows, represents the first time researchers have demonstrated drug self-administration without a caloric reward in a non-mammalian animal.

“The results are very interesting, but perhaps not unusual given the deep history of animals using plant-derived compounds, including alkaloids like caffeine and morphine,” says James Traniello, a biologist at Boston University who was not involved in the research. For example, he says, honey bees exhibit improved short term memory when they feed on plant nectar containing caffeine. “So the result in ants is quite novel, but perhaps not terribly surprising in light of the broader evolutionary picture,” Traniello says.

Not everyone is convinced that the ants in the experiment formed a true addiction, however. “It is possible that the ants in the study got addicted to morphine, but the authors don’t show evidence for addiction,” says Wulfila Gronenberg, a neuroscientist at the University of Arizona who also was not involved in the research. The findings show that morphine interacts with the dopamine system, as it does in other animals, he says. But that doesn’t necessarily mean they have developed a true substance dependence, which includes tolerance, withdrawal and behavioral effects.

“I find the paper interesting,” he said, “but this is a very preliminary study.”

Seid plans to follow up on his findings by mapping specific neurons activated by dopamine in the brains of ants. He is also collaborating with a mathematician to create models of ant social networks, to see how connections are affected when individuals in that system become addicted. “We can have a society in a microcosm,” he says. “We can dissect pieces of these networks and manipulate individuals to get a better idea of addiction’s down-cascading effects.” 

Who knows—someday, this kind of research might even help us find an ant-idote to one of society’s most entrenched problems.

Get the latest Science stories in your inbox.