Here’s how what to do after the 17-year cicadas die out

Soon, the Chicago area will stop buzzing with the noise heard only every 17 years.

The periodical cicadas, which emerge from underground in the spring every 17 years , are expected to die off by the end of June, according to Morton Arboretum scientists. When they die off, millions of the dead insects will cover the ground in suburban Chicago and much of northern Illinois.

What to do with dead cicadas and exoskeletons?

Cicada carcasses and exoskeletons that have been shed make an excellent fertilizer. To pass on their benefits to plants, scatter them in gardens or other areas you want plants to grow, suggests Stephanie Adams, the arboretum’s plant health care leader. The exoskeletons are made out of a material called chitin, which is rich in nitrogen. Nitrogen is necessary for most plant processes and is a common element in fertilizer.

“We want to encourage people to leave them in their yard, in their property, because they’re benefiting the soil, growing the soil,” Adams said. “We definitely don’t want people throwing them away.”

The cicadas will stink a little as they decompose. Running a lawnmower over the carcasses will help them decompose faster and get rid of the odor sooner, Adams said.

Cicadas can also be composted with green material like weeds or grass and brown material like dried leaves. Turn the compost often to avoid the carcasses smelling worse.

It’s also important to care for trees after the cicadas die out. A female cicada lays eggs by cutting a slit in tree branches, which can stress the tree and cause “flagging” or dying branches and patches of dying leaves. Adams recommends monitoring trees for this, but it’s rarely serious damage. Trimming the dead branches and leaves could help the appearance of the trees, but it’s not necessary, she said.

Cicada eggs will hatch in five to seven weeks, so putting the branches in mulch or on soil could help them burrow into the ground faster, Adams said.

When is it safe to remove protective netting?

Anyone who placed netting around younger trees to protect them from damage should remove it as soon as the cicadas have died off. The netting protects trees from cicadas during the season but also blocks some sunlight, Adams said. Some newer branches may have bent due to the netting, but they’ll resume their normal growth after it’s removed.

“The thing with the netting, especially if they use tulle or a material that doesn’t stretch, you’ll essentially stifle their growth,” she said. “We don’t want to strangle our trees after protecting them for so long.”

Keeping younger trees healthy by watering them regularly is especially important, and remember to water larger, more mature trees during dry spells.