The answer is vibrations.
So I read geeky news and was reading about DAS – a new use for fiber optics.
Stretching thousands upon thousands of miles under your feet, a web of fibrous ears is listening. Whether you walk over buried fiber optics or drive a car across them, above-ground activity creates a characteristic vibration that ever-so-slightly disturbs the way light travels through the cables. With the right equipment, scientists can parse that disturbance to identify what the source was and when exactly it was roaming there. This quickly proliferating technique is known as distributed acoustic sensing, or DAS, and it's so sensitive that researchers recently used it to monitor the cacophony of a mass cicada emergence. Others are using the cables as an ultra-sensitive instrument for detecting volcanic eruptions and earthquakes: Unlike a traditional seismometer stuck in one place, a web of fiber optic cables can cover a whole landscape, providing unprecedented detail of Earth's rumblings at different locations. Now scientists are experimenting with bringing DAS to a railroad near you. (From Slashdot)
But the above reminded me this is the year of Cicada emergence of two types -2024 is a special year because the cicada variant that cycles every 13 years (last one 2015) and the variant that cycles every 17 year, will all come out this year. This hasn’t happened since 1803 – and the sound is so loud that yes the DAS system which is being test to monitor Railroads – ie if rail lines have issues, landslides etc.. the sound changes/or vibrations creating alerts to warn of problems on the tracks! Will pick up the Cicada’s….. So double weird science - bugs and trains – personally I just love this!
Per the University of Connecticut site : You will be able to see all seven named periodical cicada species as adults in the same year, which will not happen again until 2037. You will not see all seven named species emerge in the state of Illinois again until 2041.
The fun on the University site was the speculation on how many Cicada’s will emerge this year – the estimate is up to a trillion adults. They also note that Cicada’s are not a pest breed of insects, don’t use pesticides on them!! Also that number is spread through out the year as different locations and Cicada variants appear on their own schedules..
From the Times article : Cicadas will become a sight to see across several states, though as few as two—Illinois and Indiana—will be able to see both broods. Brood XIII will be seen in states like Iowa, Wisconsin and possibly even Michigan. Brood XIX will emerge in Alabama, Arkansas, Georgia, Kentucky, Louisiana, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee and Virginia.
While the mating call of these insects may be annoying, cicadas are harmless to humans. They don’t sting or bite, and are not poisonous. In fact, the Environmental Protection Agency (EPA) says they can be a great food source for birds and are nutritious for the soil once they decompose.
https://cicadasafari.org/ is a great site for planning to see an emergence. At the site is a link to a phone app to find the emergence and upload your photos to Mount St Joseph University for further study! Do you plan to go see the bugs come out?