Periodical cicadas

Periodical cicadas are remarkable insects found in eastern North America. They belong to the genus Magicicada. These insects are distinguished by their unique life cycles. Most cicadas emerge every year, which is why some are called annual cicadas. However, periodical cicadas are developmentally synchronized. This means nearly all individuals in a local population emerge at once. They follow strict cycles of either 13 or 17 years. This timing is known as periodicity.

The majority of a periodical cicada's life is spent underground. They live as immature nymphs for about 99.5% of their lives. During this time, they stay beneath the soil surface. Nymphs move deeper into the earth as they grow. They use specialized mouthparts to pierce the roots of broadleaf trees. They feed on xylem fluids, which contain water, minerals, and carbohydrates. Nymphs progress through five distinct instar stages of development. It is believed they track time by detecting changes in the tree's xylem.

Emergence occurs in the spring between late April and early June. Nymphs construct tunnels to reach the surface. They often wait for the soil to reach a specific temperature. Some nymphs even build small mud turrets above the ground. They typically emerge during the evening, a time called crepuscular. This timing may protect them from predators that hunt during the day. Once they reach the surface, they climb vertical objects. They might scale trees, buildings, or even telephone poles.

After climbing, the nymphs undergo a final molt to become adults. This process transforms them into winged insects called imagos. For the first six days, they await the hardening of their wings and exoskeletons. When they first emerge, they are an off-white color known as teneral. They darken significantly within just one hour. Adult periodical cicadas have two red compound eyes. Their wings are translucent with orange veins. The males are often smaller than the mature females.

The adult stage is very brief, lasting only four to six weeks. Their primary purpose is reproduction. Males gather in groups called chorus centers. They use organs called tymbals to produce loud mating songs. These songs can reach 100 decibels in volume. Different species have different sounds. For example, the decima species sounds like a person calling "weeeee-whoa." Females find mates by responding with timed wing-flicks. After mating, females use their mouthparts to cut V-shaped slits in woody twigs. They lay about 20 eggs in each slit, totaling 600 or more eggs.

Periodical cicadas use a strategy called predator satiation to survive. They emerge in massive numbers, sometimes exceeding 1.5 million individuals per acre. This overwhelming abundance ensures that predators cannot eat them all. Birds, squirrels, and mammals will eat many, but many cicadas will survive to reproduce. Scientists believe the 13- and 17-year cycles are prime numbers for a reason. These specific intervals make it harder for predators to synchronize their own life cycles with the cicadas. This helps the cicadas avoid being eaten every time they emerge.

These mass emergences have significant impacts on the environment. The feeding of nymphs can cause tree growth to decline the year before emergence. Moles often thrive on the abundance of nymphs before the emergence occurs. However, mole populations may drop the following year when food is scarce. Wild turkeys benefit greatly from eating the adults on the ground. Even the dead cicadas help the forest. Their decomposing bodies provide a massive pulse of nutrients to the ecosystem. This cycle connects the underground world to the life of the forest above.