When crickets emerge, it can get a little wet
This spring, when ground temperatures reach 64 degrees Fahrenheit, trillions of crickets will dig their way up from underground in the southern and midwestern United States. In a rare so-called double emergence, two different cicada broods – one with a 13-year life cycle and the other with a 17-year life cycle – will take to the trees to sing, eat and mate.
And while we might prefer not to think about it, given their residence in the branches above, the crickets will also eliminate waste in the form of urine. Despite their size, crickets have an impressively powerful current, scientists reported in an article article published on Monday in the journal Proceedings of the National Academy of Sciences.
The researchers adapted a fluid dynamics framework, based on features such as surface tension and the effects of gravity, to map how animals of different sizes, from mosquitoes to elephants, can urinate.
“It’s this beautiful physics perspective” of seeing all the data in a single graph, says Saad Bhamla, a bioengineer at the Georgia Institute of Technology who co-authored the study.
The research shows that the urine streams that crickets produce travel at a speed of up to 3 meters per second – the fastest of any animal assessed in the new study, including mammals such as elephants and horses.
Scientists have extensively studied how creatures in the animal kingdom eat and drink, but few have delved into the mysteries of fluid excretion. Still, there are many reasons to study how different animals urinate, said Dr. Bhamla. Understanding how animals’ bodies have evolved to solve their waste problems, for example, could provide new ideas for mouthpiece design.
There are also ecological implications to the research. Cicadas drink 300 times their body weight in xylem, a nutrient-poor plant sap, every day. All that moisture has to go somewhere. Yet the environmental impact of this significant flow of cicada urine is completely unknown.
For Dr. Bhamla is the spirit of inquiry sufficient motivation. “We are a curiosity-driven laboratory,” he says. And what first piqued his curiosity about insect urine was a bizarre observation in a group of insects called sharpshooters.
Dr. Bhamla and a PhD student, Elio Challita, have captured videos of snipers excreting their urine one drop at a time and then using a special appendage to catapult each drop away from their bodies at ultra-high speeds.
That finding was consistent with a study from a decade ago, which found that mammals larger than about 5 pounds urinated in jets, while smaller ones couldn’t produce enough pressure and therefore simply dribbled.
Snipers are small so they can’t shoot fighter jets. But as xylem feeders, they have a lot of liquid to dump, the researchers reasoned, so they had developed an energy-efficient drip approach.
But while conducting field research in the Peruvian Amazon, the researchers spotted a cicada that emitted a stream of urine that defied the measure.
Dr. Challita, who co-wrote the new study and is now a postdoctoral researcher at Harvard, studied the urination habits of as many insects as he could find, both in real life and on YouTube videos, and dove into some calculations.
Surface tension forces make it increasingly difficult to push liquid out of a tube as the tube becomes smaller. Cicadas are about four to eight times larger than sharpshooters, so their plumbing is not subject to the same restrictions. But they still have to use energy to overcome those forces.
Cicadas hold the record for the strongest jet stream relative to their size, although butterflies and bumblebees can also produce jets. However, mosquitoes, aphids and flies have to settle for dripping.
Dr. Challita and Dr. Bhamla adapted two measurements to map the urinary performance of 15 animals of different sizes. These measurements track the role of surface tension, gravity and inertia in the way fluids are secreted from a tube such as the urethra. In larger species, including humans, gravity and inertia are critical to how quickly the body can expel urine and how easily surface tension forces can be counteracted.
“But on a small scale, gravity is not that important,” explains Dr. Challita out. “That’s where biology comes into the picture.” Surface tension takes over, making jet urination a more expensive process in terms of energy, although crickets are large enough to lend a helping hand through inertia. Their bodies can bear the cost of vigorous urination, the researchers speculated, and evolution has judged the energy well spent.
“Cicada urination occurs in a quite unique region of fluid dynamics, where both inertia and capillary forces simultaneously play important roles relative to gravity,” said Sunghwan Jung, a biological and environmental engineer at Cornell, who was not involved in the study. the work was involved.
Dr. Bhamla said there is a lot of room for future research in the field of droplet or flush secretions. Understanding the fluid dynamics at play allows researchers to more closely examine why an animal uses one solution over another.
“I just think it’s so cool,” he said. “It made Elio and me happy to find this out.”