Cicadas are coming back in 2024 primarily due to a rare, synchronized emergence of two major periodical cicada broods—Brood XIII and Brood XIX—each following its distinct life cycle, alongside localized, off-cycle appearances from other broods. This creates a remarkable and widespread natural event across the United States.
The Great Cicada Double Emergence of 2024
The overwhelming reason for the significant cicada presence in 2024 is the simultaneous emergence of two distinct groups of periodical cicadas, an event that last occurred over 200 years ago.
Synchronized Cycles: Brood XIII and Brood XIX
Periodical cicadas adhere to either a 13-year or 17-year life cycle, spending most of their lives underground as nymphs before emerging en masse. In 2024:
- Brood XIII (The Northern Illinois Brood): This 17-year brood is emerging primarily across northern Illinois, parts of Wisconsin, Iowa, Indiana, and Michigan. Its last emergence was in 2007.
- Brood XIX (The Great Southern Brood): This 13-year brood, the largest of the 13-year cicadas, is emerging across a vast swath of the southeastern U.S., from Missouri and Illinois down to Georgia and South Carolina. Its last emergence was in 2011.
The co-occurrence of these two broods is a rare phenomenon, last observed in 1803, when Thomas Jefferson was president. Their emergence is driven by environmental cues, primarily soil temperature reaching a specific threshold (around 64°F or 18°C), signaling them to tunnel to the surface.
Off-Cycle Appearances: Early Birds from Other Broods
Beyond these massive main emergences, 2024 also sees instances of smaller, off-cycle cicada appearances. For example, some cicadas from Brood XIV and Brood XXIII are emerging. This occurs because 2024 is one year before the anticipated 2025 emergence of Brood XIV and four years ahead of Brood XXIII's expected return in 2027, leading to some individuals appearing early in their respective ranges. These "stragglers" or "pre-emergers" are not part of the main synchronized event but contribute to the overall cicada presence.
What to Expect During a Cicada Emergence
When millions or billions of cicadas emerge, several notable phenomena occur:
- Loud Noises: Male cicadas produce distinct, loud buzzing or whirring songs to attract mates, creating a pervasive chorus that can reach decibel levels comparable to a lawnmower or a jet engine.
- Sheer Numbers: The ground can be covered with cicadas, their exoskeletons, and their nymphs.
- Harmlessness: Despite their numbers, cicadas are harmless to humans and pets. They do not bite or sting. They pose little threat to mature plants but can damage young trees or shrubs by laying eggs in branches.
Geographic Reach of the 2024 Emergence
The areas experiencing cicada emergences in 2024 are widespread, covering a significant portion of the eastern and central United States.
| Brood | Life Cycle | Primary States Affected |
|---|---|---|
| Brood XIII | 17-year | Illinois, Wisconsin, Iowa, Indiana, Michigan |
| Brood XIX | 13-year | Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Virginia |
| Off-Cycle | Varies | Localized emergences in areas corresponding to Brood XIV (e.g., Ohio, Kentucky, Tennessee, Pennsylvania, West Virginia, Maryland, Virginia, North Carolina, New Jersey) and Brood XXIII (e.g., Arkansas, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, Tennessee), typically on the edges of their main ranges. |
Understanding Cicada Life Cycles
Periodical cicadas spend the vast majority of their lives underground, feeding on sap from tree roots. After 13 or 17 years, depending on their brood, they emerge synchronously, shed their nymphal skins, mature into adults, mate, lay eggs, and then die, all within a few weeks. The new eggs hatch, and the young nymphs burrow back into the ground to begin the cycle anew. This unique biological clock is what drives their predictable, yet rare, mass appearances.
