In the summer of 2024, two tribes consisting of billions of warriors emerged from the ground in the South and Midwest US regions. These clans were Brood XIII and Brood IX, two families of periodical cicadas that surfaced simultaneously in an event not witnessed for over two centuries. Although these insects were destined to die for the survival of their broods, they came to the region in peace.
Periodical cicadas spend the majority of their lives tucked under the ground, developing. When they reach adulthood, they surface for only three to four weeks to mate, lay eggs, and die. Depending on the brood, these puzzling insects appear every 13 or 17 years. In late April and early May of 2024, these emergences coincided for the first time since 1803, the year of the Louisiana Purchase.
The mystery surrounding periodical cicadas earned them the genus Magicicada — and it isn’t difficult to understand why these creatures may be regarded as magical. In their short time above ground, male cicadas emit an extraordinarily shrill mating call. Due to the sheer number of insects, these calls create an overwhelming cacophony. But how are they capable of producing one of the loudest calls in the insect kingdom?
These unassuming brown insects are just one to 1.5 inches in length, with characteristic orange-red eyes and transparent wings. Despite their small size, residents in the Midwest discovered first–hand last summer that these little creatures create powerful sounds. This noise is partially explained by the sound–producing organ called the tymbal, located at the side of the insect’s abdomen. The insect’s muscles quickly vibrate the tymbal membrane, buckling the ribs inward at their midpoint and producing a fast sequence of individual clicking sounds, typically about 150 to 320 per second. This noise is then amplified by their hollow abdomen. If a cicada was a one–man band, the tymbals would be the eager drummer and the abdomen would be the amphitheater.
Truthfully, even this understanding of cicada anatomy does not completely explain the sheer volume of a cicada call. Mathematical models were developed and published by US Naval researchers to attempt to represent the tymbal phenomenon using a modeling function called the nonlinear least squares technique. The researchers aimed to find the secret underlying force of the cicada sound in hopes of applying this knowledge to an underwater sonar device — such as those used by fishermen for discovering schools of fish — with the same capacity for sound broadcasting as these insects. Despite these efforts and progress in understanding cicada capabilities, the models were not sufficient to pinpoint the exact methods of sound amplification, and the project has not been resumed since.
“If a cicada was a one–man band, the tymbals would be the eager drummer and the abdomen would be the amphitheater.”
As for their second quirk, why do cicadas appear in such a regular, yet seemingly arbitrary schedule? This question also lacks a comprehensive conclusion. However, scientists have floated a few theories. First, cicadas are speculated to possess a strong molecular clock that functions as a built-in alarm clock, instructing the insects to surface at the exact 13 or 17–year mark. Another theory suggests they rely on environmental cues through subtle shifts in underground tree sap prevalence as trees progress through their lifecycle. Once the correct number of cycles pass, periodical cicadas understand that their own cycle is concluding.
Whether one of these theories or a combination of both is the key to understanding this pattern, the exact mechanism is ambiguous and perhaps always will be.
For Boston residents wondering when it will be their turn to experience a periodical cicada emergence, the answer is very soon. In the summer of 2025, Brood XIV returns to Cape Cod and surrounding regions, sure to bring a lot of noise and maybe even a little bit of magic.