Chrystelle L. Vilfranc
Imagine spending 17 years underground preparing for your big debut just for a fungus to ruin your moment.
For some of the periodical cicadas of Brood X, there’s no need to imagine. It's their reality.
Brood X is in Indiana for the first time in 17 years, and it’s one of the biggest broods in the country.But the emergence of the cicadas is accompanied by a deadly fungus. Not only does this fungus control the cicadas’ minds and behaviors, but it also interferes with the cicadas’ whole purpose above ground, which is to procreate.
This fungus is rare enough that it will not wipe out the cicada population long-term, but its affects could be key to new scientific understandings, in part, because of its unique chemical makeup that allow it to alter the behavior of its cicada host.
“(The fungus)stays in the soil for another 17 years until the next brood emerges,” said Elizabeth Barnes, an exotic forest pest educator at Purdue University. “They’re the only organism, that we know of, that actually specializes on the 17-year cicadas.”
What is Brood X?
Periodical cicadas have been well studied and documented by scientists since the 1700s.
With a short survival time above ground, the cicadas enjoy flying around, singing and mating. Barnes describes a drum-like organ called a tymbal that the male cicadas contract against their hollow abdomen to sing or call. This creates the alien-like sound you’ve likely heard if you live in an area where cicadas have been spotted.
'Otherworldly':For the first time in 17 years, millions of cicadas will be swarming Indiana
The purpose of the cicada emergence is for the cicadas to lay eggs and mate. Once the female cicadas are lured to the trees, they click their wings to signal their interest, and the pair will begin to mate.
The females will then find healthy trees to lay their eggs. Once they do this, the adult cicadas will die, and the nymphs will tunnel into the ground where they’ll stay for the next 17 years, sucking on the sap of tree root. After their 17 years underground, they will begin to emerge and restart the life cycle.
That is, if the parasitic fungus doesn’t get to them first.
The zombie apocalypse plaguing cicadas
A parasitic fungus, called Massospora cicadina,infects the cicadas during both the mating and emergence processes. This can happen when the fungus releases infectious spores into the tunnels cicadas build in the soil and when infected cicadas come into contact with other cicadas.
The first thing that happens to an infected cicada is that it loses its genitals. This leaves the lower half of the cicada’s body looking like a “gross chewed up Kleenex,” Barnes explained. This white area, she said, is a collection of the spores of the fungus that are stuck at the end of their bodies, which can eventually fall off, as well.
Once the cicada loses its lower half, the fungus will release chemicals that allow it to order the cicada’s actions.
Then, the fungus begins its mind control.
“(The fungus)produces chemicals that makes the cicadas stay active, even though normally when a cicada has a severe injury, it becomes very sluggish. If not … eventually dying,” Barnes said. “It makes it more active.”
The secret to the fungus’ conquest lies in the chemicals it transmits, a study in Fungal Ecology finds. The aim of the fungus is to promote its spread across the cicada population, so rather than killing the cicadas, this fungus keeps its captors alive and active to fulfill its infectious agenda.
The chemicals also possess the “zombified” cicadas with an increased sex-drive. Despite no longer having genitals, infected male cicadas are so desperate to mate that they will click their wings like the female cicadas, which then attracts healthy males.
But it’s a trap: The healthy males, ready to mate, will instead be infected by the zombie cicada.
These cicadas behave differently from the cicadas who are infected by spores in the soil. Instead of looking for mates, these will shed fungal spores along the ground that will remain in the soil for another 17 years, waiting to infect the next generation.
Cicadas have existed for more than 5 million years. Now, humans threaten their future.
'We're not in control of everything'
This mind-controlling, parasitic phenomena is not unique to cicadas.
Keith Clay of Tulane University compares the mind-controlling effects of fungus to a closely-related fungus that creates zombie ants. These infected ants climb up trees and bite leaves to spread the infection. The ant will die, and the spores of the fungus are left to be released as it rains.
As billions of cicadas are above ground there are more opportunities to identify the zombie cicadas by their white butts; however, Barnes suggests that they are not actually widespread. Luckily for the Brood X cicadas, she said, only a subset of them will be infected.
If you’re determined to spot a zombie cicada, Clay advises visiting areas that the cicadas are most abundant, like the Indiana University campus. Rather than occupying more natural areas such as the Brown County State Park or Hoosier National Forest, Clay said, the cicadas actually prefer suburban and urban areas with lots of trees, like golf courses and university campuses.
“(The cicadas)really thrive the best in association with humans and human structures and landscape modifications,” Clay said.
While some people — and dogs — have found the cicadas to be an interesting snack, Barnes strongly advises against eating any of the infected cicadas. She cautions that the potential effects of the fungus on humans have not been studied in detail, and it would be safer to refrain from snacking on them.
How long is cicada season? And what happens to them? Here are some answers.
This cicada season is loud and sometimes bothersome; however, Clay said he feels the cicada season can provide a lesson. People are often in control of the world around us. With the periodical cicadas, however, depending on your location, it can be difficult to escape their presenceor their loud singing.
Much like the zombie cicadas lose control of their minds, Clay believes that this cicada season reminds humans that we are unable to control everything, especially natural phenomena.
“Despite our advanced civilization we cannot control a lot of natural phenomena,” Clay said. “And in the case of cicadas, it’s not a threat. … I think it’s a healthy thing for us to realize that we’re not in control of everything.”
Chrystelle Vilfrancis the 2021AAAS Mass Media Fellow at the Indianapolis Star. She earned her PhD in Cancer and Cell Biology from the University of Cincinnati earlier this year. She studied drug-induced liver disease progression. She's on Twitter as @drchrysvilfranc.
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