In many classic horror stories, mad scientists often turn masses of people into mindless zombies to make them follow their dastardly bidding.
The same is true in the animal kingdom where a particular species of caterpillar uses its sugary secretions to lure in droves of ants and turn them into its own unwitting servants.
A team of scientists at Japan's Kobe University have discovered how the larvae of Japanese oakblue butterflies are able to protect themselves against predators by compelling ants to become their bodyguards.
The Narathura japonica caterpillars, which are known to grow while wrapped inside oak tree leaves, was first thought to have a mutually beneficial arrangement with Pristomyrmex punctatus ants to have the tiny insects protect the larvae from wasps and spiders that might try to eat them.
Kobe researcher Masaru Hojo, however, noticed that the larvae were always attended by the same individual ant repeatedly.
Hojo said that it appeared as if the ants never left the larvae or returned home to their nests. He pointed out that the ants even abandoned the idea of looking for food, and they simply decided to stand around and guard the caterpillars.
In their experiment, Hojo and his fellow researchers collected ants and allowed some of the insects to feed on the caterpillar's sugary secretions, while the rest of them were kept in a separate place.
The ants that consumed the secretions from the caterpillar stayed close to the larva and did not go back to their nest.
Whenever the caterpillar flipped its tentacles to turn them inside out, the ants would suddenly move rapidly around in an aggressive manner.
According to the researchers, they saw similar ants in the field attack predatory wasps or spiders, suggesting that this action could be a way for the caterpillar to order its ant servants to attack these insect threats.
Hojo noted the presence of granular cells located near the caterpillar's tentacles, which could be the ones secreting the chemical signals to the ants. He believes that chemical and visual signals from the larva could be the cause of stimulation for the ants to become aggressive.
The ants that the researchers separated from the caterpillar and did not consume its sugary secretions did not react when it flipped its tentacles.
This finding demonstrates a possible direct connection between the chemical composition of the secretions and the ants' behavior.
To find out more about this observation, Hojo and his colleagues treated the ants with reserpine, a drug that prevents the transmission of dopamine.
When the treated ants were exposed to the flipping of the caterpillar's tentacles again, they did not show any response similar to their earlier reaction. This suggests that dopamine does play an important role in the ability of the larva to control the ants.
The chemical composition of the caterpillar's sugary secretions has not been identified yet.
The results of the study hint that the mutualism between the caterpillar and the ant, which can also be found in other relationships of species, could be considered a form of behavior that is manipulative parasitic in nature.
Indian Institute of Science Education and Research's John Mathew said that the findings of the Kobe University researchers are perspective-changing. He said that he would like to see the experiment's effect on other mutualistic relationships between species.
Martin Heil of the National Polytechnic Institute in Mexico, however, argued that the situation was not fully explored in the study.
"The benefit for the caterpillar is obvious, but we do not know whether the benefit for the ants is as minimal as the authors argue," Heil said.
"If the liquid that the caterpillars secrete is sufficiently nutritious, then it might well be that the overall balance for the ants also is positive."
The Kobe University study is published in the journal Current Biology.
