Dopo 17 anni ritorna l'invasione delle cicale

By
Jason SamenowWeather editor (TWP)

Despite chilly weather, cicadas have begun to emerge in considerable numbers throughout the Washington region. This marks the beginning of the much-anticipated Brood X cicada outburst, a once-every-17-years event.

On Capital Weather Gang’s Twitter feed, we’ve received dozens of reports of the insects in Northern Virginia, Maryland and the District.

Monday morning brought a sudden increase in sightings after only isolated reports of early cicadas in the past one to two weeks. The emergence was somewhat unexpected given the lower-than-normal temperatures since Friday.

Despite the surge of reports, the insects haven’t crawled out of their holes everywhere, and a more massive swarm still awaits.

“My opinion is that these emergences are still localized and spotty, in small numbers, and not widespread — at least in what I was able to observe,” Daniel Gruner, a professor in the University of Maryland’s entomology department, wrote in an email Monday. “All of the sites I am monitoring have no emergence, the instances we saw were localized to single yards, with just a handful of individuals. The adults have been hard to find this morning.”

Paula Shrewsbury, also a professor in the University of Maryland’s entomology department, wrote that the cicadas appearing Monday are on the early side of a bell-shaped curve for their emergence, which typically begins in late April, peaks in the second half of May and trails off in June.

It’s possible that the cicadas seen on Monday were lured to the surface by mild temperatures Sunday afternoon and the warm night that followed, in which temperatures rose to near 70 during the predawn hours before plunging into the 50s as a cold front passed.

Both Gruner and Shrewsbury wrote they were “surprised” by the cicada reports Monday, considering soil temperatures have dropped since early last week. Cicadas don’t tend to emerge until soil temperatures reach 64 degrees, and they are not that warm.

“Of the sites I am monitoring, our maximum soil temperatures were 62, but many were back to 59 or 60,” Gruner wrote.

With predicted highs in the 60s and lows in the 40s to near 50 through Thursday, soil temperatures won’t warm much, if at all, so it’s possible the cicada nymphs settle down some. “It will be interesting to see what happens in the next few nights,” Shrewsbury wrote.
Forecast highs and lows from a blend of computer model forecasts for the next 10 days. (WeatherBell)

Highs in the 70s and lows in the 50s are forecast by the weekend and early next week, which may bring a much more massive and widespread emergence of the cicadas.