Everyone knows the sound of cicadas in summer — loud and ubiquitous. But this year, get ready for an extraordinary event: billions of cicadas will emerge simultaneously in a rare and fascinating natural spectacle. This unique convergence, occurring only once every 221 years, involves two major groups of periodical cicadas. Their simultaneous emergence, driven by distinct 13-year and 17-year life cycles aligning, has captured the attention of both enthusiasts and biologists. To fully appreciate this event, it’s crucial to understand the differences between these periodical cicadas and the more familiar annual cicadas. Let’s delve into their lifecycles and explore these distinctions.
Cicadas, both annual and periodical types, are recognized for their distinctive lifecycle. Spending most of their lives as nymphs underground, they undergo various growth stages while feeding on tree root sap. This prolonged development, unique among insects, prepares them for their short but crucial adult phase, which is a key aspect of their biology.
This lifecycle starts a new phase when rising soil temperatures, typically around 64° F, trigger cicada nymphs to emerge from underground. As they surface, the nymphs shed their exoskeletons in a process known as molting, transitioning into their adult form. At this stage, the cicadas begin their mating activities. Adult males start their distinctive mating calls, an essential part of this process. After mating, female cicadas lay their eggs in slits they carve into tree branches. The eggs hatch in about six to ten weeks. The new nymphs burrow into the soil to start their life underground. This cycle of emergence, molting, mating, egg-laying, and burrowing is characteristic of all cicadas.
Annual cicadas, known for their familiar buzzing sounds, are a hallmark of summer. Despite individual life cycles lasting 2 to 5 years, they emerge every year due to overlapping generations – thus the label annual cicadas. This consistent emergence contrasts with the infrequent, synchronized appearances of periodical cicadas. Additionally, annual cicadas are typically larger and can have hues of green, brown, black, and sometimes even blue or white, setting them apart from the smaller, black-and-red periodical cicadas.
In contrast to the annual cicadas, the natural world also witnesses the phenomenon of cicada broods. A cicada brood is defined as a large group of cicadas that emerge simultaneously after a long period of underground development. In the eastern half of the United States, there are 15 identified periodical cicada broods, categorized into twelve 17-year cycles and three 13-year cycles. Each of these broods, recognized by a Roman numeral, makes its appearance in specific geographical regions at different times. A notable example is the expected emergence of Brood XIX and Brood XIII in 2024, indicated as light blue and brown in the map below. The simultaneous emergence of two broods in the same year is a rare event because their distinct life cycles—separated by either 13 or 17 years—seldom align, making such an occurrence an exceptional natural spectacle.
Brood XIX, a 13-year cicada brood renowned for its vast extent and broad distribution, is expected to make a striking emergence in late spring to early summer of 2024. Notably, this brood is beginning to emerge in North Alabama, where I live. This brood is notable not only for its size but also for its expansive geographic reach. The emergence of this brood is often marked by a notable variety in their mating calls’ intensity and frequency. These calls, varying in pitch and rhythm across different regions, create a rich auditory tapestry reflective of the brood’s diverse habitats.
Not to be outdone, Brood XIII, on a 17-year cycle, is set to make its appearance in 2024 as well. Last seen in 2007, this brood primarily occupies areas in Illinois, Indiana, and Iowa. Unlike their 13-year counterparts, Brood XIII cicadas display unique characteristics. Their song is typically deeper and more resonant, distinguishing them from other broods. Visually, they may exhibit variations in color patterns and wing vein layouts. Additionally, Brood XIII prefers denser woodland environments, resulting in a visually concentrated and striking emergence.
These are photos Mrs. G and I took in early May while searching for cicadas in and around Huntsville, AL. They capture various stages of the cicada lifecycle, showcasing their emergence and unique behaviors.
The upcoming cicada broods showcase the intricate cycles of nature and the fascination they spark among us. As billions of cicadas emerge, their symphonic sounds and vivid presence will envelop the regions they inhabit, illustrating life’s resilience and the enduring mysteries of the natural world. If you are lucky enough to live in an area where cicadas are emerging, take advantage of this unique opportunity and experience it firsthand. This grand display is poised to leave a lasting impression on all who witness it.