For the last thirteen years, Brood XIX, or the Great Southern Brood of periodical cicadas have been living underground as nymphs, feeding on hardwood plant roots. If a mature tree wasn’t present 13 years ago, if the tree was cut down since that time period, or if the tree is not a hardwood species, cicadas will not be present. This May, billions of juveniles will emerge and mature into adult cicadas, and the majority will be dead by the first week of June.
The periodical cicada, or magicicada septendicim is a term for seven different species of cicadas known for their 13- and 17-year life cycles. The life cycle of the cicada starts as an egg laid in the bark of young twigs. After 6-10 weeks, the eggs hatch and nymphs drop to the ground where they burrow approximately two feet into the earth. There the nymphs feed on the xylem fluid of plant roots and undergo five instar stages of development over the next 13 or 17 years depending on the species. In May or June of the emergence year when soil temperatures are warm enough, the nymphs burrow out of the ground and climb onto nearby vegetation where they molt and harden their exoskeletons. Adult cicadas only live a few weeks after emergence, with their primary purpose during emergence being reproduction. Males produce loud mating songs to attract receptive females, who will mate just once and then lay her eggs. These eggs begin the next life cycle of periodic cicadas.
Adult periodical cicadas are typically around 1 inch in length with females larger than males. They have translucent wings with orange veins and a black dorsal thorax. The underside of the abdomen varies in color depending on the species but can be black, orange, or striped. The mating call of a male cicada will vary based on its species. The good news for people and plants is that cicadas are relatively harmless. They do not sting, are not venomous, and do not transmit diseases. Mature plants rarely suffer lasting damage from cicadas, though new or young plantings should be protected from the insects by cheesecloth or a similar material to prevent feeding and egg-laying damage.
One of the big questions is why these insects live in 13- or 17-year cycles. There are a few ideas on why that is, but it primarily revolves around a survival trait called predator satiation. Essentially, for the first week after emerging, cicada nymphs are very vulnerable prey for other animals. The goal of having billions of nymphs emerge at once is to simply overwhelm predators with sheer numbers- they can only eat so much, after all! In addition to this, it’s theorized that the long underground period and odd-year emergence cycle helps prevent predators from becoming dependent on cicadas as a food source and prevents predator populations from synchronizing with the cicada life cycle. Additionally, it is theorized that any individuals that do not adhere to the life cycle of the masses would quickly be picked off by predators and thus eliminated from the gene pool.
If you see Brood XIX in your county, feel free to download and report the sighting in the iNaturalist app! Otherwise, let us know if you have any questions at uge3181@uga.edu or 706-359-3233.
