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Periodical Cicada adult

In spring 2024, headlines about a synchronized emergence of millions of cicadas from two broods spread across the internet and news media. Many people panicked about what damage these broods would cause to trees and plants and anxiously prepared for the once-a-lifetime event to occur. The double-brood emergence did occur in the United States. However, to either your disappointment or relief, it did not happen in Alabama.

What is a cicada brood?

Cicadas of the same life cycle that live in the same region and emerge in the same year are said to belong to a single cohort called a brood. This is to say that a brood can contain cicadas from multiple species if they are adults in the same 13- or 17-year cycle at the same time. It is like a school graduating class: a group that reaches the same milestone together. There are twelve broods of 17-year cicadas and three broods of 13-year cicadas. Each brood is assigned a Roman number.

The two periodical cicada broods with synchronized emergence in 2024 were the 13-year Brood XIX and 17-year XII. These broods made their emergence from their yearslong underground stay, with trillions of wingless nymphs crawling out of the ground and climbing up trees to emerge as the winged adult. The winged cicadas buzzed loudly for a rush of mating and laying eggs in tree twigs before they died. Before their adult stage was over, they produced the next generation, which will spend 13 or 17 years sipping on root xylem sap before emerging from the ground and repeating the life cycle.

Figure 1. The 13-year periodical cicada adult.

Figure 1. The 13-year periodical cicada adult. (Photo credit: Blake Layton, Mississippi State University)

The 13-year Brood XIX occurs across 14 eastern states, including Alabama, but the 17-year cicada Brood XII only occurs further north in Illinois, Indiana, Iowa, Michigan, and Wisconsin. Therefore, only those living in areas where the two broods overlap witnessed the striking, double-brood emergence. This only occurred in parts of Illinois and Indiana.

Periodical versus Annual Cicadas

In 2024, Alabamians will see more annual cicadas than periodical cicadas.

In eastern North America, the genus Magicicada has seven periodical species. Periodical cicadas are long-lived insects that only emerge from the soil periodically. Three species spend 17 years underground. The other four species spend 13 years underground to complete most of their life cycles. Periodical cicadas that emerge every 13 or 17 years are unique to the eastern United States. Periodical cicadas do not occur statewide in Alabama. They primarily occur in areas in central and northern Alabama. The periodical cicada species are relatively smaller than annual cicadas and have red eyes, black bodies, and orange wing veins (figure 1).

In addition to the periodical cicadas, there are also more than 160 annual cicada species in the United States. Annual cicadas typically have a brood every year during in the summer and in smaller numbers than periodical cicada broods. Their life cycle generally spans 2 to 5 years. They are usually green, brown, and black in color with green eyes (figure 2). On average, they are a little larger than periodical cicadas.

The Cicada Life Cycle

Figure 2. The annual cicada adult.

Figure 2. The annual cicada adult. (Photo credit: Blake Layton, Mississippi State University)

Cicadas are relatively large insects in the order Hemiptera, the same order as aphids and plant lice. Cicadas share a three-stage life cycle: egg, wingless-nymph, and winged-adult.

Adult cicadas live for only a few weeks and are the only life stage that can fly. The lifespan is just long enough to find a mate and lay eggs. Males make the characteristic high-pitched sounds throughout the day to attract a female to mate. Females do not make any sounds. After mating, females will lay eggs on twigs of more than 200 hardwood tree types. Both male and female cicadas suck plant liquids for nutrition.

Eggs are laid by female cicadas inside small tree branches or twigs. Females use a sharp ovipositor to cut a series of narrow slits into the bark of hardwood tree twigs, where they deposit their eggs (figure 3). A female may make multiple series of slits in various places. Eggs stay inside the tree branches/twigs for about 6 to 8 weeks. The nymphs then hatch and fall onto the ground, digging into the soil in search of roots to feed on.

The nymphal stage is spent underground, sucking sap from the roots of hardwood trees. Nymphs undergo five molts and grow larger each time. The development durations vary significantly among the types: annual (2 to 5 years possible), 13-year, and 17-year. At the end of their fifth nymph stage, they dig out of their underground niche and climb up onto the closest tree (or surface). This typically occurs a few hours after sunset and after a rain in summer. Nymphs then shed their old exoskeleton and emerge as winged adults.

What damage do they cause?

Figure 3. Damage on a redbud tree from cicadas laying eggs.

Figure 3. Damage on a redbud tree from cicadas laying eggs.

Cicadas are harmless insects to humans and animals. They do not bite, sting, or transmit any diseases. Although not ordinarily considered a pest, egg-laying activities can damage young samplings and cause dieback. Heavily damaged twigs by egg laying may droop or break off. The wounds created by females may not heal and could be susceptible to disease infections. However, healthy and mature trees can better tolerate cicada damage.

Enjoy the Cicadas!

Since damage is not a major concern, people can sit back and enjoy the presence of cicadas in several ways:

Cooking Cicadas. Cicadas, particularly newly hatched nymphs, are a good source of protein. They are high in crude protein, low in crude fat (2.6 grams per 100 grams), and contain a mix of essential and nonessential amino acids, making them a complete protein source. Try washing the nymphs or newly emerged adults and then marinating them with salt or teriyaki sauce before cooking. They can be cooked by frying, roasting, grilling, or other ways to make cicada-inspired meals. They can be a delicious treat to try.

Artwork. You can create or enjoy cicada-inspired artwork, such as books, wall art, postcards, keychains, pins, stickers, and mural illustrations.

Observe and be Cicada-Inspired. 

  • US military scientists have invented a cicada-inspired mini drone.
  • Researchers have invented a cicada-inspired subsoiling tool.
  • Medical researchers also invented cicada-wing-inspired nanomaterials to kill bacteria and fungi on contact.