Cicadas and their threat to trees

I was planting a fern the other day and unearthed a plump, brown creature that resembled a peanut hull, a wriggling hull.

I felt badly about disrupting this periodical cicada. It lived its entire life — 17 years — for a party that had yet to stir. What's the point of being a lone cicada? Like the billions of others that will soon shape our landscape, this one started out as an egg in a tree, hatched into an ant-sized nymph and fell to earth. Over the years, it burrowed deeply, grew in several spurts and fed on the sap of our trees.

Something deep within the insect told it that this particular spring was the one to leave the cold blackness of the soil world to emerge from a tunnel of its own making, once the ground temperature reached 64 degrees.

For most 17-year cicadas, a life of dreary subterranean existence is capped by a bacchanalia that would put the most dissipated rock star to shame: We’re talking fame, orgy, earsplitting music and death. There will be little time to eat.

But there will be time to lay more eggs, which must bother the gardener because of the attendant damage to branches. With so many cicadas — as many as 1 million per acre — we will be cleaning up after the party for a while to come.

The cicadas will emerge by month's end, to sing, mate and reproduce, in a six-week frenzy that is worrying every June bride from here to New York and beyond. Tree huggers have cause to fret as well, though the sky won't fall.

Soft stuff, such as perennials, annuals, tropicals and garden veggies, is safe. It’s the woody plants that are at risk, though evergreens are not favored by the insect.

Females lay eggs in a slit they make in bark, preferring young branches that are about the thickness of a pencil and a bit stouter. Many of the branches will heal by forming calluses, but others won’t recover, especially if visited by many egg-laying cicadas. The vegetative growth above the injury will turn brown and die, and the twigs may keel over. Arborists call this “flagging.”

By August, some leaf canopies may look tatty on the edges, but new growth next spring will repair the damage. Shrubs may take a hit, but their twigginess works in their favor.

The greater threat is to young ornamental trees that have been planted in the past two years or so because they are full of optimally sized branches important to the tree’s future shape and growth.

Fruit trees are also prime targets. Frank Gouin, who planted a peach orchard at his farm near Deale, recalls the effects of the cicadas the last time this cohort, called Brood II, appeared in 1996. “The branches would just fall off,” he said. This included branches with developing fruit.

Experts say that insecticides will not significantly reduce cicada populations, and who wants to spray poison all over the place? The two-inch insects don’t sting or bite and have a grotesque beauty about them, with red eyes and orange wing veins. Some people call them locusts, which they are not. The males make a racket, calling for a mate.

For egg-laying, the females seem to prefer oaks, maples, redbuds and cherry trees, though they will damage scores of other species, and they are drawn particularly to trees at the edge of a woodland, said Michael Raupp, an entomologist at the University of Maryland.

If you are worried about precious, small trees, you can put three-eighths or finer netting over the tree, but do this before the cicadas appear in number around Memorial Day. Raupp has co-written a guide for netting, available online at www.bugoftheweek.com.

I have a redbud beneath an oak tree that may well take a hit, but it is too big to net. I am more worried about a young, slender paperbark maple that I planted in the fall.

I got it from Tom Moseley, a nurseryman in Potomac, and told him of my plan to shroud the tree in netting. “Has to be all the way around, and secure the bottom,” said Moseley, of Maryland Gardens Tree and Shrub Farm. “They just swarm.”

This will be his fourth Brood II encounter. The first was in junior high school when he and others offered a classmate a dollar to eat one. “He ate about half of it before he threw up,” he said. “We gave him the dollar anyway.”

If you are planning to install a new landscape with lots of young trees and shrubs, you may want to wait until early fall to plant it. This would be a better time, generally, to do major plantings, to spare transplants the stress of summer.

I now discover, though, that I need to worry about my pond fish as well as the young trees.

“Large numbers of decomposing cicadas could cause problems with oxygen depletion in the water,” according to the Maryland Home and Garden Information Center’s online fact sheet.

The idea of bug carcasses piling up will no doubt help the hype that comes along with Brood II. But there is no point in getting anxious. Better to see it for what it is, an amazing bout of strangeness. For a bug, 17 years is a long time to wait to see the world, and for anyone attuned to nature, the anticipation is exciting. I measured my soil temperature earlier this week at 58 degrees.

Over the next few days, the nymphs will climb up tree trunks, fences and walls and then peel out of their shell in resplendent adult form. You will see many dime-size holes in garden beds.

“It’s a remarkable phenomenon,” said Raupp. “It’s got everything wonderful — birth, death, romance, sex, a spectacular natural event for people to witness and enjoy. It is something that should be welcomed in amazement rather than feared.”

Read past columns by Higgins at washingtonpost.com/home.

@adrian_higgins on Twitter

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Cicadas and their threat to trees