As if the 17-year emergence of cicadas from the earth beneath our feet wasn’t already as strange as a horror movie, scientists have now discovered that the fungus covering some of the bugs controls their behavior in a zombie-like way.
Last year, researchers at West Virginia University discovered that some cicadas fall prey to a fungus after they emerge from their 13 or 17-year rest underground. The spores from that fungus form a “plug” on the bugs by dissolving the cicadas’ genitals, butts, and abdomens. If there’s a bright side in any of this for the cicada, it’s that when the fungus interacts with the cicada, it forms cathinone, a plant-based amphetamine found only in the Horn of Africa and the Arabian Peninsula, and psilocybin, the compound that makes you “trip” when you eat magic mushrooms.
In addition to helping the cicada not realize that a good portion of its body has been dissolved, new research shows that these compounds might also cause the cicada to engage in tricky behavior to help spread the spores. Reporting in the journal PLOS Pathogens, the research team showed that infected male cicadas begin exhibiting a female mating pattern by flicking their wings. This lures other males to the bugs who then also pick up spores, get infected, and do the fungus’ bidding all over again.
Taking Free Will for Granted
Brian Lovett, study co-author and post-doctoral researcher with the Davis College of Agriculture, Natural Resources and Design, likens the fungus’ commandeering of the cicadas’ behaviors to rabies, in the way in which the disease uses the host to spread itself.
“When you’re infected with rabies, you become aggressive, you become afraid of water, and you don’t swallow,” Lovett said. “The virus is passed through saliva, and all of those symptoms essentially turn you into a rabies-spreading machine where you’re more likely to bite people.
“In that sense, we’re all very familiar with active host transmission. Since we are also animals like insects, we like to think we have complete control over our decisions, and we take our free will for granted. But when these pathogens infect cicadas, it’s very clear that the pathogen is pulling the behavioral levers of the cicada to cause it to do things which are not in the interest of the cicada but is very much in the interest of the pathogen.”
Lovett and his colleagues are not quite sure just where the fungus comes from; it could infect the nymphs as they burrow underground and lie dormant for more than a decade, or the bugs could pick up the fungus as they emerge during their 13-17 pattern. Either way, the team emphasizes that cicadas are harmless, which made them easy to study.
“They’re very docile,” Lovett said. “You can walk right up to one, pick it up to see if it has the fungus (a white to yellowish plug on its back end), and set it back down. They’re not a major pest in any way. They’re just a really interesting quirky insect that’s developed a bizarre lifestyle.”