Buzz
For years, scientists have examined the interaction between Japanese oakblue butterfly (Narathura japonica) caterpillars and nearby ants (Pristomyrmex punctatus). The caterpillars secrete a sugary substance for the ants to consume, and in return, the ants guard the caterpillars as they develop within the oak tree leaves.
However, Masaru Hojo from Kobe University in Japan recently noticed that each caterpillar was always accompanied by the same ants, which “never strayed or returned to their nests,” he explained to New Scientist. Could something in the sugary secretions be causing the ants to lose interest in everything except the caterpillar, even neglecting to search for food to nourish themselves?
To explore this theory, Hojo and his team conducted laboratory experiments where some ants were allowed to interact with the caterpillars and consume the sugary secretions, while others were kept apart as a control group. The control ants that didn’t consume the sugar droplets were free to come and go, but those that ingested the secretions remained with the caterpillar, abandoning their nests. Additionally, whenever the caterpillar extended its tentacles, the ants began to act aggressively. In contrast, ants that hadn’t consumed the secretion were unaffected by the caterpillar’s behavior. It seemed the secretion was altering the ants’ behavior, almost as if it were drugging them, transforming them into zombies under the caterpillar’s control.
Hojo believes that the caterpillar's control over the ants may serve as a defensive strategy in nature. Instead of defending itself, the caterpillar causes the ants to act aggressively in response to predators. “There are glandular cells near the tentacles that might be secreting chemical signals,” Hojo explained. “Both visual and chemical cues could be triggering the ants' aggression.”
The researchers, whose findings were published in a recent issue of Current Biology, are unsure exactly what aspect of the secretion grants the caterpillar control over the ants. However, it seems to involve dopamine. The ants exposed to the secretion showed lower dopamine levels, and when treated with reserpine—a drug that blocks dopamine transport—even those ants that consumed the secretion ceased responding to the caterpillar's tentacle movements.
Hojo and other scientists not involved in the research suggest that these results challenge the concept of many interspecies relationships as mutually beneficial. However, some are not so quick to reject the traditional views.
“The advantage to the caterpillar is clear, but we cannot be certain that the ants’ benefit is as minimal as the authors suggest,” said Martin Heil, of the Center for Research and Advanced Studies of the National Polytechnic Institute in Irapuato, Mexico, in an interview with New Scientist. “If the liquid the caterpillars secrete is sufficiently nutritious, the overall balance for the ants may also be positive.”
