Cicadas are singing their summer melody four years earlier than expected in some areas, a surprise that has experts looking for answers.
In recent weeks, University of Maryland professor of entomology Michael J. Raupp has been documenting the signs of cicada nymphs' early emergence from their underground resting places.
"I have observed a surprisingly large emergence of periodical cicadas in several locations in central Maryland," Raupp said. "The guys are up in the treetops singing their hearts out with the big boy band trying to attract a mate. The gals are being choosy."
The cicadas are thought to be part of Brood X, the largest of 15 periodical broods that appear en-masse across portions of the eastern United States, normally in 17-year cycles.
"Their bizarre strategy is to emerge in such great numbers that they overwhelm the feeding capacity of their predators, leaving enough behind to perpetuate the species," Raupp said.
In their immature stages, cicadas stay underground for either 13 or 17 years, depending on their brood. When the time is right, they head to the surface and emerge at night, dashing to vertical structures like tall trees to shed their skin.
Once their exoskeletons harden, the males head to the treetops to mate and the females lay their eggs in the branches before they die. The eggs take about four to six weeks to hatch before the new cicadas tumble back down to the earth, dig underground, and nourish themselves with the sap from tree roots over the next 17 years, allowing the cycle to repeat.
"Brood X is the largest emergence of periodical cicadas in the universe," Raupp said."It is called the big brood, trillions of cicadas emerging from Georgia to Michigan, Illinois to New York."
Brood X last made an appearance in 2004, and wasn't expected to return until 2021. Their emergence in some areas ahead of schedule is proving to be a mystery to scientists. Some believe weather and climate may be one possible reason for the acceleration.
However, the numerous biological, genetic and environmental variables that impact insects like cicadas make it difficult to deduce a true cause for their off-schedule arrival, Raupp said.
While March temperatures around Baltimore Washington International Airport, roughly 10 miles from Raupp's location in Columbia, were close to normal, February was one of the warmest on record, according to AccuWeather Meteorologist Jim Andrews.
"The average high for February was 56.1 degrees Fahrenheit with an average low of 32.3," Andrews said, citing that the normal average low is usually in the middle to upper 20s.
February also saw record-breaking highs this year on Feb. 7 and Feb. 8 when temperatures climbed to 72 degrees Fahrenheit. Another 77 F day came in at 8.4 degrees above normal, nearly breaking a record set in 1874, Andrews said.
"Some cicada experts believe that the warming of the world may have accelerated Brood X to emerge," Raupp said, but added that early arrivals are not unheard of.
Accelerations like the one happening in 2017 have been observed in the past, including accelerations of Brood X in the Maryland area. A smaller brood, Brood VI, is currently starting to appear in parts of Georgia and the Carolinas.
"I would like to see more data before I attribute this to a climate change phenomenon," he said. "Like most biological events, this is likely an interaction between genes and environment."
Weather does, however, play a vital role in the behaviors of cicadas, Raupp said.
On cool, rainy days, the animals are far less active than they are on a warm, sunny days where temperatures climb into the 80s.
"These are not simple things," he said, stating that available resources, genetics, climate and other environmental factors all affect the way animals behave. "We just don't know everything."
In the meantime, Raupp said he will continue to make regular updates on his findings through his Bug of the Week blog, which has a detailed record for Maryland's early arrivals.