The shrill call of cicadas in the trees has been waning, and by July 4, the loudest noises in the air should be fireworks.
Kelly Hougland, a doctorate candidate at University of Missouri-Columbia, left Washington June 9 as he wrapped up his research on brood V cicadas – well before the adults and their loud mating calls started to die off as their 17-year life cycle comes to an end.
“There were hot spots at Abernathy Field Station where I was doing my research where it was tough to have conversations because it was so loud,” Hougland, 33, said, “but it wasn’t unbearable.”
The 110-decibel calls were music to his ears as he studied emergence patterns of the noisy arthropods. Hougland plans to reveal an abstract on his studies of how the insects potentially communicate and coordinate underground before their mass emergence in late spring. His preliminary results will be published at www.academia.edu ahead of the Animal Behavior Society conference he’s speaking to July 30 to Aug. 3.
Most residents in Washington are welcoming the relative sound of silence that has been missing since early May, but the cicada phenomenon is not over yet.
“Look for pencil-size twigs and branches on trees at the end of summer. They’ll likely be dead branches. And you’ll see the nymphs emerging from the half-inch slits where the females laid their eggs,” Hougland said.
The nymphs will look like little, white shrimp the size of a grain of sand. And they’ll rain down upon the earth to burrow near the roots of trees – that is if the branches don’t fall from the incisive injuries to the tree, bringing the mite-sized cicada babies down with them. Hundreds of billions will drop to the surface near the base of trees and start burrowing to get to the roots. It’s a timely journey as the trees switch prioritizing nutrient distribution from the trunks and branches and into the roots for winter, where the nymphs will feed on the water-rich xylum fluid. But most of the billions upon billions of nymphs won’t make it through their first two winters.
“Only two percent of them will survive over the next two years,” Hougland said, “and we’re not really sure how or why that happens. Competition for nutrients is one major theory, because we won’t see much overlap of the broods in regional shifts.”
It’s not known why the mortality rate is so high, but there are other theories Hougland has heard. And he said it’s an area for future research.
“Since they feed on such nutrient-poor material, their gut material and microbes most likely depend on nutrient diversity, just like we need probiotics. For specialist insects that’s even more important since they’re only taking in xylum fluid so it’s just water with minerals and amino acids. The microbes give them the rest of their nutritional needs. It’s like reaching into a bag of M&M candies and you need yellow ones to survive, but you may only get one or two or none at all in some instances,” Hougland said.
An evolutionary aspect of the cicadas’ mating cycle helps to deter this at least a little bit, according to Hougland.
“When the female lays an egg, some of that gut microbe makeup is laid with it. But if it’s raining heavily, or that attached glob of microbes gets washed away or removed, that may be a problem that contributes to their mortality rate,” he said.
But Hougland and the rest of the entomologist community doesn’t know for sure. And he doesn’t know for sure yet if his thesis about cicada nymphs chatting about the weather to mass emerge for their best chance for survival is true, either. In fact, he’s precluded from talking specifics about his research until it’s published. But he did let on that not everything he observed was what he expected.
“They were coming out during the day, and other odd times, when they usually emerge at night. So that was weird,” Hougland said.
Hougland has since cleaned up his research site at Abernathy Field Station in Amwell Township. But the rest of us will be sweeping away cicadas and stepping on crunchy shells through August.