Serrapilheira Institute
Using condoms, scientists studied the towers built by cicadas in the Amazon.
Known for the characteristic sound they produce, cicadas are a group of insects that encompass more than three thousand species different spread across the world.
But a typical Amazonian species, Guyalna chlorogena, draws attention for its curious behavior: builds small clay towers mixed with urine as it comes out of the ground.
According to Pedro Pequeno, professor and researcher at the Serrapiheira Institute and the National Institute of Science and Technology SinBiAm (INCT-SinBiAm), cicadas begin to most of life undergroundfeeding on the sap of the roots.
When they are in the final phase of their lives, already leaving the ground to undergo metamorphosis and become adults, these insects build the towers.
“The towers gradually rise, night after night, they [as cigarras] they build it little by little, over a few months”, he details.
Although the towers are relatively well-known in the Amazon region, Pequeno says that their function was unknown.
And this intrigued a group of Brazilians who were taking a course in the Amazon.
“From the beginning, on the exploratory trails, the cicada towers caught our attention, they they looked like a fairy village that came out of the ground. And what was most curious is that there was no explanation for this”, says biologist Marina Méga, a doctoral student at UFRJ who was part of the group.
After all, what is the purpose of these towers?
Hypotheses
Two hypotheses were developed by the researchers. The first was that these structures served as a protection and defense mechanism of cicadas, reducing the risk of them falling victim to a predator during the nymph period.
“Because when it reaches this stage of metamorphosis, the cicada comes out, emerges and sheds its skin to assume its adult form, but this process takes a long time, and when it does this, it remains stuck there on the outside of the tower, motionless. If a predator appears there, it dies“, explains Pequeno.
The fact that the tower contains urine also raised the possibility of serving as a kind of repellent to deter predators.
The second hypothesis is that the towers allowed gas exchange so that the cicadas could breathe inside the structures.
“The soil is an environment with little oxygen and a lot of carbon dioxide, so these small animals that live in the soil naturally undergo an adaptation to deal with this situation”, explained Pequeno.
To test this hypothesis, an unusual idea came up: use condoms to seal the towers.
“We looked at the towers, we found the shape a little peculiar. And so, jokingly, one of my colleagues suggested using condoms”, said Marina Méga.
The idea was simple: if the tower really served to exchange gases, the tendency would be for the condom inflated with carbon dioxide that it was coming out of there, through the small pores of the clay.
And that’s exactly what happened.
“The condom started to swell and we saw that there was some kind of gas exchange. We were euphoric. We started to celebrate, to sing. Anyway, we had this moment of great happiness. It was a victory, because we were in an inhospitable environment, with relatively few resources”, recalls the biologist.
After the test, the team of researchers ordered around 40 condoms to confirm the gas exchange hypothesis and carried out other experiments with ant baits to check whether the towers also served as a way for cicadas to protect themselves from predators.
In the end, both hypotheses proved to be true.
“From a scientific perspective, it is something that fills in gaps in what we already have, in what we knew. knew little about these structureshad a more morphological perspective, more observational studies, but no hypotheses were really tested about these functions. And the functions of these structures can increase the survival of cicadas, and this is of great biological importance”, highlighted Ména.
Largest cicada tower ever seen in the world
It is believed that not all species of cicadas build these towers. But there is record of at least a type of this insect on each continentaccording to Pequeno.
However, what draws attention to the towers studied in Manaus is their size. During experiments in the Amazon, researchers found a 47-centimeter tower, the largest ever seen in the world.
“The Amazon towers are much larger than all the others we have documented. Generally, the towers that reach 8, 10, maximum 12 centimetersthey don’t go much further than that. And the ones we observed in Manaus, this was already described in the literature, could reach up to 40 centimeters. And then, walking there, we found a tower measuring almost 50 centimeters,” said Pequeno.
The results of this discovery in the Amazon, which was made in an unusual way, gave rise to a scientific article that, according to Pequeno, should be published soon.
“Understanding functions of biological structures is useful because much of what we do in the world is imitate biological structures. Often we, researchers, are trying to imitate the natural process that already exists in an extremely efficient way. If we can understand how cicada towers work, this could have numerous implications for gas exchange, thermal control, for example.”
