As if Rappahannock farmers don’t have enough to worry about with what could be a record number of brown marmorated stink bugs expected to emerge this spring, masses of another bug – the periodical cicada – are also due to come out about the same time.
While cicadas in all 155 species emerge each year in staggered shifts, only seven species are “periodical,” emerging en masse every 13 or 17 years. One or more of these species, in the Magicicada genus, make up each “brood.” The 15 broods thought to exist today are distributed along most of the east coast of North America, some with overlapping ranges. Virginia is home to six broods.
The 17-year Brood II, or East Coast Brood, is the only one on record as emerging in Rappahannock County, and the next emergence should be this year. Its range extends from southeast New York to northwest North Carolina and stretches along either side of the Blue Ridge Mountains, through the heart of the state’s fruit-tree industry. While cicadas prefer oaks, they have a wide range of hosts, including apple, dogwood, peach, hickory, cherry and pear.
Although the epicenter of Brood II is in Pennsylvania, which should have the highest density of the bugs, says Smithsonian Conservation Biology Institute entomologist Jim McNeil, he and Virginia Tech entomologist Doug Pfeiffer both said in recent interviews that they wouldn’t be surprised to see 1 million per acre emerge in some areas in Virginia.
They add that distribution maps are not always reliable because much of the historical data on where the broods emerge is anecdotal and, with the long intervals between emergences, changes in the land (such as destruction of forests) can have a big effect on the bug’s populations. McNeil points out that the Magicicada Mapping Project, using modern technology, is updating the maps, which are available at Magicicada.org.
Cicadas lay their eggs in trees. When the eggs hatch, the nymphs that emerge head for the tree’s roots to feed, staying underground for 13 or 17 years, depending on the brood. In this stage, the cicadas’ impact on the host tree is “questionable,” especially on fruit crops, says Pfeiffer. While some research indicates their feeding can suppress a tree’s foliage production, he points out that growers typically try to divert a tree’s resources to developing fruit rather than foliage anyway, so it’s hard to sort out the bug’s effect from that of humans.
In emergence years, the Magicicada nymphs simultaneously climb out of the ground when the soil temperature reaches about 65 degrees. They molt into winged adults whose sole purpose is to breed, after which they die. McNeil says that, although adult cicadas can fly, they tend to stick close to their host tree, so emergences can be highly localized.
While adults don’t feed, females can damage tender tree stems when they use their saw-like ovipositor to excavate shallow trenches in the stems to deposit their tiny white eggs. The resulting “flagging” – dead, brown leaves and stems above the scars – may not have a big impact on mature trees, but can affect the growth pattern of young ones. McNeil says one entomology professor he knows refers to cicadas as “nature’s pruners.”
Cicadas are large – around 1.5 inches. Most periodical adults have black bodies, orange-red eyes, transparent wings, and orange leg and wing veins. Although they are “grotesque and frightening in appearance, cicadas do not bite and are actually harmless to handle,” Lang Elliott and Wil Hershberger write in their book “The Songs of Insects.”
Shape, behavior and calling signals differentiate the various cicada species. Both genders have calls, but it’s the males’ loud humming, produced through special membranous hearing organs in their abdomens, that aggregate cicadas into groups for breeding, usually in the morning. The females, have “really good” hearing, says McNeil, and can easily determine a male’s location and calling intensity.
Females respond by flicking their wings, which makes a clicking sound that draws the males to them. In Virginia, Magicicadas usually start humming in mid-May but can start as early as April. The adult population peaks in mid-June and dies off by mid-July. Annual cicadas breed later, in late July or early August.
The Virginia Cooperative Extension puts information on expected brood emergences in its annual spray bulletin and advises commercial growers to factor them into their planting plans. Although tree-fruit crops may take a hit from Magicicada emergences, “the impact is relatively minor on most trees,” says McNeil. The best strategy for anyone wanting to plant young trees this year, say both entomologists, is to wait until fall, after the bug’s breeding season is over.
For those who want to protect trees already planted, netting is the most environmentally friendly option, say both entomologists. Pfeiffer adds that a recent study found that this is cost effective even in orchards. The Extension’s fruit-growers’ website has a link to a commercial netting supplier. For protecting just a few trees, tulle from a fabric shop should work fine, says McNeil. The nets need to cover all branches of the trees and be secured tightly around the trunk to keep cicadas from crawling up under it.
Pfeiffer also recommends an organic product, Surround At Home Crop Protectant. Its main ingredient is kaolin clay, which clogs insects’ orifices. It can also be washed off trees easily after the Magicicadas breed and before it will have much of an impact on predatory-insect populations, which mature later in the summer, says McNeil. Rappahannock CFC manager Mike Cannon says he plans to order the product for the co-op.
The Magicicada’s loud humming, masses of bodies crunching underfoot and weird looks make them unpopular with most people, but the insect’s emergence offers several ecosystem benefits. While they’re more likely to perish from the fungal disease Massospora cicadina than from predation, a variety of insect-eating birds, mammals, reptiles and insects, including the specialized cicada killer wasp, will likely get a population bump from Brood II’s emergence.
“It’s basically going to be a big buffet,” McNeil says.
Cicadas are palatable and have no natural defenses, such as toxins, to keep predators at bay and instead evolved a “predator satiation” strategy common with some animal species. With the huge, all-you-can-eat buffet offered by the Magicicadas, predators quickly fill up, leaving many of the cicada’s young to survive. With the long interval between the bug’s emergences, most predators also don’t live long enough to get their hunting and reproductive strategies enough in sync with the bug to do real damage to its populations, McNeil says.
Although predator populations should get a bump, this likely won’t be sustained in subsequent years and populations should cycle back down to pre-outbreak levels, McNeil says. Most other insects have better defenses against predation than the cicada and are not as rich a food source, so predators are not likely to shift to them after the Magicicadas are gone, McNeil says.
Native ecosystems get another benefit from the Magicicadas’ emergence: When they die, their decaying corpses provide nutrients to the very trees upon which the nymphs had fed and on which future generations will feed in the never-ending energy cycle.
For more on periodical cicadas, including maps, sounds and photos, visit CicadaMania.com, the Extension’s fruit-growers’ website (virginiafruit.ento.vt.edu/cicada.html) or contact Rappahannock County Extension agent Kenner Love (540-675-3619 or firstname.lastname@example.org).
Cool cicadas facts
- Cicadas are “quite tasty,” says McNeil, who sampled some during the Brood X outbreak in 2004. “They were fantastic – they actually had a little bit of a meat to them as opposed to other insects you might eat.” He fried them up, lightly breaded, he says, and found them “delicious.” However, he does advise taking off the wings and legs first “so they don’t get stuck in your teeth.” David George Gordon, in his “Eat-A-Bug Cookbook,” includes a recipe for cicada-topped pizza. “Bug appétit,” he says. Although Gordon warns that overindulgence is the only risk, McNeil says that people with shellfish allergies should be careful, since there are crossover allergies between shellfish and cicadas, which are distantly related.
- While pets are likely to eat cicadas, overindulging could cause minor stomach upsets that can lead to these insect meals coming back up. In their enthusiasm, pets might also choke on the insects, so owners should monitor their pets’ consumption of the bugs.
- Cicadas are often incorrectly called locusts, which are in a separate order of insects that includes grasshoppers.
- The loud insect humming on summer nights in Virginia is often attributed to cicadas, but actually comes from katydids, which are a related species. Cicadas are diurnal, typically humming in the morning in the spring.
- David Attenborough, in an episode of PBS’ “Nature” program, demonstrated how females attract males by the flicking their wings, which makes a clicking sound. Attenborough snapped his fingers near a male cicada, moving his hand back and forth at the same time. The male cicada kept moving to follow the sound, eventually landing on Attenborough’s face.
- Some researchers have noted that 13 and 17 are prime numbers and are exploring whether this is significant in how populations of the various broods, and of predators, relate to each other.