Are humans next?
Even people may not be fully immune to such manipulation. Much of our modern-day behavior seems to suit the interests other species, such as hitchhiking invasive species and airline-riding viruses that hop continents in a matter of hours. But can we also be manipulated from within?
To a certain degree, yes. Perhaps the most familiar example is rabies, which can cause human hosts—like other mammals—to salivate excessively, thereby spreading the deadly virus. Researchers have even shown that malaria-infected people are more attractive to mosquitoes, which spread the infected blood to another host, according to a 2005 PLoS ONE paper.
Such pernicious parasitism is indeed widespread throughout various kingdoms. "We know it's evolved a few times," Exeter's Hughes says. So, he wonders: "Has it been different solutions to the same problem?"
In the quest to understand both how these uncanny behaviors work and how they emerged, researchers are also enlisting the help of evolutionary ecology. They are examining these behaviors on a smaller scale. For example if two larvae are growing on a controlled host, like the P. argyra orb-web spider, what happens to the spider's behavior when one is mature and the other isn't yet ready to emerge?
Some hosts have evolved to cope with frequent parasitism. For example, one beetle that is frequently killed off early by a parasite has adapted by increasing its sexual activity and producing more offspring, Thomas notes.
But the chilling question remains: How can bugs control other bugs? And in some of the more extreme examples, Hughes ponders: "How can a member of one kingdom modify the behavior of another kingdom?" Until scientists find that answer, it's all eerie action, for sure.