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Cicadas are dying off, but leaving behind a stench

They should be mostly gone within one to two weeks. We’ve mapped where they’ve been present.

Dead cicadas are collecting on the ground. (Daniel Gruner for The Washington Post)

Have you noticed dead cicadas on the ground, or that the bugs are not chorusing as loud as during past weeks? It’s because cicadas reached peak numbers last week in and around the D.C. area and are starting to die at a rapid rate.

In some places, you may be smelling them as they rot away.

“As we move past the peak, the dead [cicadas] are starting to pile up, returning their nutrients to the soil,” wrote Daniel Gruner, a professor of entomology at the University of Maryland, in an email.

That decay process is producing an odor. I’ve recently picked up on a foul stench while walking my dog and, yes, cicadas are to blame.

“When animals die they have a pretty distinct BAD smell,” wrote Paula Shrewsbury, also a professor of entomology at the University of Maryland, in an email. “As part of the decay process there are a number of interactions between enzymes and microbes that result in the ‘smell of death.’ Cicadas are no different than other animals; when they die they smell bad.”

“This smell will continue until the cicadas are dried out and/or decomposed,” she continued. “The upside is that by dying, the cicadas are returning nutrients back in the soil under trees that will support their young for the next 17 years.”

Fear of cicadas is real and common. It’s also far from unfounded.

With the number of dead cicadas mounting while the chorusing of the ones still alive becomes fainter as the days pass, when will they be gone entirely?

“From past cycles, broods last about 4-6 weeks from their first emergence,” Gruner wrote. “We are about one month in, and we see they are diminishing. I do expect they will be largely gone in 1-2 weeks. I will mourn their passing.”

Gruner said he expects the cicadas to hang around longest in our cooler areas west of Washington, such as Leesburg and Winchester, where they were last to arrive.

Shrewsbury agreed. “Since the length of the life cycle of adult cicadas should be more or less the same, areas where cicadas emerged later should have adult cicada activity later,” she wrote.

Cicada coverage map

With the goal of mapping 2021 cicada sightings across the D.C. area, we polled our readers on Facebook to determine where the bugs have been found. We received over 5,000 responses with our first poll and over 1,000 responses with our second poll.

That’s too many data points for me to plot on a map, so instead, I took a large sample of our readers’ data and plotted the locations.

Our 2021 cicada coverage map is displayed above. The red shading shows where Brood X cicadas were reported during the 2004 emergence, and the red dots are Capital Weather Gang reader-supplied cicada sightings this spring.

Cicada splatters on cars are a sticky mess, and can damage paint

We learned the 2004 cicada coverage map plotted the southern border of Brood X cicadas incorrectly. The southern extent of Brood X cicadas extends into eastern Prince William County and across northern Charles and Calvert counties. And the cicada hole displayed over southern Loudoun County on the 2004 map was wrong. Our readers reported cicada sightings in that area. But overall, the 2004 map was pretty accurate for most of the area.

Keep in mind, if you live in a subdivision that was cleared of topsoil when it was developed, there is a good chance your yard does not have cicadas, even if you live inside Brood X territory.

One last note, I’ve heard from some of our readers that they believe this year’s cicada emergence produced more cicadas than they remembered in 2004. If that’s true, we should be overrun with cicadas 17 years from now. I can hardly wait for their return.