Cicadas are insects recognized for their distinct songs and periodic emergences. They inhabit a variety of environments across the globe, from forests to deserts. These insects spend the majority of their lives underground as nymphs, feeding on fluid from plant roots. After years of development, they surface as adults for a brief period focused on reproduction.
Evolutionary Ancestry of Cicadas
The cicada’s story begins in the fossil record. The earliest ancestors of modern cicadas, belonging to the superfamily Cicadoidea, first appeared in the Mesozoic Era, with the oldest known fossils dating to the Triassic period. These ancient insects are part of the order Hemiptera, or “true bugs,” which also includes aphids and leafhoppers. This classification distinguishes them from locusts, which are a type of grasshopper and a common confusion.
Fossil evidence provides a glimpse into their ancient form. These fossils reveal that early cicada nymphs possessed strong forelegs adapted for digging, much like their modern counterparts. This suggests a subterranean lifestyle, feeding on plant roots, was established early in their evolutionary history. While their modern relatives in the family Cicadidae are known for loud sound production, Mesozoic cicadas may have been relatively silent, similar to the relict family Tettigarctidae found today in Australia. Phylogenetic analyses indicate the two main cicada lineages likely diverged by the Middle Jurassic.
Geographic Beginnings and Global Spread
Scientific evidence points to Asia as the likely continent of origin for cicadas. From this heartland, they began a global journey spanning millions of years. This dispersal was influenced by continental drift and fluctuating global temperatures. As landmasses shifted and conditions changed, new habitats became available, allowing cicada populations to expand.
This expansion led to the establishment of cicadas on every continent except for Antarctica. Today, there are over 3,000 cicada species worldwide, each adapted to its specific environment. North America is home to over 170 species, while South and Central America have at least 800. This wide distribution demonstrates their adaptive success in colonizing diverse ecosystems.
The Emergence of Periodical Life Cycles
The long, synchronized life cycle is a well-known cicada behavior unique to the genus Magicicada in eastern North America. These periodical cicadas emerge in massive numbers after spending either 13 or 17 years underground. This strategy is not found in other cicada species, which appear annually. The evolution of this precise cycle is believed to be a survival mechanism driven by environmental pressures.
A leading hypothesis for this synchronized emergence is predator satiation. By surfacing all at once in overwhelming numbers, the population satiates potential predators like birds and small mammals. There are too many cicadas for predators to consume, ensuring many survive to reproduce. This mass emergence makes individual survival a matter of probability rather than a contest of fitness against a predator.
The use of 13 and 17-year cycles, both prime numbers, provides a mathematical advantage. This prime-numbered interval makes it difficult for the life cycles of their predators to synchronize with their emergences. A predator with a shorter life cycle of three or four years will rarely encounter the cicada boom, preventing the predator population from specializing in response.
The formation of distinct “broods,” or year-classes, was likely influenced by the climatic shifts of the Pleistocene ice ages. As glaciers advanced and retreated, they fragmented cicada populations into isolated geographic pockets. This isolation allowed different groups to evolve their 13 or 17-year cycles, giving rise to the different broods observed today.