Cicadas

Cicadas are well-known on the East Coast for their epic numbers, mind-numbing noise, and littering trees and shrubs with exoskeletons. What I didn’t know was the West Coast has cicadas, too. And this is the year, coast to coast, they all come out of the ground to mate in record numbers.

Newly emerged cicada (Ollllonate) CC BY-SA 4.0

Cicadas (Magicicada) are grouped by species and broods. Periodical cicadas include M. septendecim, M. cassini, and M. septendecula species. Each species has 13-year broods, 17-year broods, and different cycles of each of those broods. Each cycle is labeled with a Roman numeral.
Limited numbers of cicadas emerge any one summer. This year is different. This year, we will see the co-emergence of several cycles of both 13-year and 17-year broods. This generally happens every 221 years. Lucky us.

As you may know, I use sticky barriers around the trunks of my fruit and nut trees to thwart crawling insect pests. These barriers also let me see which insects are out and about, though the sticky sheets hanging in the trees do a much better job of that. I was surprised to find cicada exoskeletons caught in the barriers protecting my navel citrus tree. I thought cicadas were only on the East Coast, but I was mistaken.

Cicada exoskeleton caught by sticky barrier (Kate Russell)

Types of cicadas
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Cousin to leafhoppers, there are more than 3,000 types of cicadas globally and more than 170 species in North America (that we know of). There are two cicada families: one lives in Australia, and the other lives everywhere else (except Antarctica). Within that family, there are annual cicadas and periodical cicadas. Periodical cicadas are native to North America. They spend most of their lives underground as nymphs. Here, they feed on sap from tree roots.
 
Annual cicadas

Most annual cicadas emerge annually, though they can spend up to 9 years underground. Unlike periodical cicadas, the emergence of annual cicadas is not synchronized. Annual cicadas are also known as jarfly or dog-day cicadas because they tend to emerge mid-summer. I probably had annual citrus cicadas (Diceroprocta apache) in my California garden, though several other cicada species were present.

Annual citrus cicada (xpda) CC BY-SA 4.0

Cicada description and lifecycle

Cicadas are true bugs with large, red, wide-set eyes, transparent forewings, and short antennae. They are stocky, substantial bugs that are generally active during the day. While the Malaysian emperor cicada is nearly 3 inches long with a wingspan of up to 8 inches, most cicadas are significantly smaller than that, and thank goodness! Most adult cicadas, or imagos, are 1 to 2 inches long with comparably smaller wingspans.

After mating, female cicadas cut slits in the bark of twigs where they lay their eggs. When the eggs hatch, the nymphs are pale and about the size of a grain of rice. They drop to the ground and use their strong front legs to burrow as much as 8 feet into the soil. Here, they will feed on xylem sap from the roots of trees and shrubs. They prefer ash, cypress, maple, oak, and willow, but will feed on other trees, as well. In the final instar, they return to the surface where they shed their skins and emerge as flying adults. Those shed skins are commonly found attached to trees.

Swarm of live and dead cicadas at the base of a tree (knorby) CC BY-ND 2.0

Cicada sounds

If you’ve ever been present for a cicada emergence, you know how incredibly noisy these insects can be. At up to 120 dB, they are the noisiest insects on Earth. They are so loud that they can cause permanent hearing loss when experienced at close range.

I lived in Virginia during an emergence year. It was an experience I’d rather not repeat. While not as bad as the Midwest’s plague of locusts, cicadas were everywhere. They coated windshields, driveways, and roads. They flew into you, clinging to your clothes and hair. The noise was enough to drive any sane person crazy. And then it was over. Like it never happened, except for the hollowed-out exoskeletons attached to every tree you saw. But finally, it was quiet.

Both males and females have membranous structures called tympana that detect sounds. When a male cicada sings, he turns his tympana off so as not to damage his own hearing. {I used to have a neighbor like that. I had to move to a new apartment.]
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Male cicadas create all that noise using organs called tymbals found on their abdomen. In some species, both males and females rub their wings over a series of ridges found on the thorax. These bugs have resonating cavities and membranes that amplify the sound. While we can’t tell the difference, it ends up that each male cicada has a unique song composed of modulated clicks that sound, to us, like continuous notes. I have to assume that the female cicadas can tell the difference. To me, they’re very noisy. I did learn that one of the Australian cicada species does not produce audible sounds. Instead, they produce vibrations transmitted through whatever tree they are on, which sounds far more civilized. And some cicada songs are so high-pitched that we can’t hear them. Another interesting note about cicada courtship is that different species may be found on the same tree but at different levels.

A cicada drying itself after molting (Martin Nielsen) CC BY-SA 4.0

Adult cicadas feed on sap from xylem tissue, but they generally do not harm mature trees and shrubs. Newly planted trees and shrubs should be protected with netting during emergence years. In most cases, cicada root feeding is not significantly destructive. Females have been known to lay eggs on asparagus, citrus trees, date palms, and grapevines.

As temperatures rise, cicadas stop nibbling the roots of your plants and emerge from the soil to mate, lay eggs, and die. Ants, bats, birds, squirrels, spiders, and wasps will all gorge on cicadas this year. While cicadas do not bite or sting, they are also not very bright and may mistake you for a tree and try to feed.

Don’t bother spraying pesticides or insecticides for cicadas. The damage they do is minimal and you would have to use gallons of the toxic stuff to counteract a periodic emergence. If you cannot tolerate the noise, use it as an excuse to spend a week in Hawaii.

Cicadas are eaten in many parts of the world. In China, nymphs are deep-fried. Supposedly, they are pretty tasty when dipped in chocolate. I don’t think I’m ready for that just yet. The French onion crickets were about as far as I feel comfortable.