Red Eyed Cicadas Crawl Up Oak Trunks in Midwestern Emergence

In the damp, warming soils of the American Midwest, an ancient, subterranean clockwork has just completed its silent countdown. For nearly two decades, billions of wingless nymphs have tunneled through the dark, sipping the watery sap of deciduous tree roots in absolute obscurity. Then, in a synchronized response to soil temperatures hitting a critical threshold of 64 degrees Fahrenheit, they breached the surface, transforming the quiet forest floors of Illinois, Indiana, and Missouri into a crawling, iridescent carpet of life.

This spring marked a historic biological event: the simultaneous emergence of the 17-year Brood XIII and the 13-year Brood XIX. Not since 1803, during the presidency of Thomas Jefferson, have these two specific cohorts of periodical cicadas (genus Magicicada) risen from the earth at the exact same moment. The resulting spectacle has provided entomologists with an unprecedented living laboratory to study evolutionary biology, predator satiation, and ecological disruption on a continental scale.

The Mechanics of a Prime-Numbered Underground Vigil

The survival strategy of periodical cicadas is one of nature’s most baffling and elegant mathematical puzzles. Unlike annual cicadas, which appear every summer, periodical cicadas spend either 13 or 17 years underground. Both of these intervals are prime numbers, a biological trait that evolutionary biologists believe is designed to prevent predators from synchronizing their own life cycles. If a predator species operated on a two-, three-, or four-year population cycle, it could never regularly coincide with the emergence of the cicadas, preventing the evolution of specialized cicada-hunting predators.

During their long subterranean exile, the nymphs are far from dormant. They undergo five distinct developmental stages, or instars, tunneling through the soil and clinging to the fine rootlets of oaks, maples, and ashes. They feed exclusively on xylem fluid, a nutrient-poor liquid that flows upward through the plant. Because xylem is mostly water and dissolved minerals, the nymphs grow at an agonizingly slow pace, requiring more than a decade to accumulate the energy reserves needed for their final transformation.

When the internal clock finally strikes, the nymphs dig vertical exit tunnels, often constructing little mud chimneys at the surface if the ground is exceptionally wet. They emerge in the cover of darkness to minimize their exposure to birds and small mammals. Climbing up the nearest vertical surface—be it a tree trunk, a wooden fence post, or a blade of grass—they anchor their claws, split their nymphal skins down the back, and slowly pull their soft, milky-white adult bodies into the night air.

The 2024 Co-Emergence: A Rare Spatial Overlap

The 2024 event is particularly significant because of the geographic proximity of the two emerging broods. Brood XIII, primarily located in northern Illinois, southern Wisconsin, and eastern Iowa, met Brood XIX, which stretches across the southeastern United States and up into central Illinois. This created a narrow zone of contact where the two populations overlapped, offering a rare opportunity to observe potential interbreeding and ecological competition.

Entomologists from across the globe converged on this transition zone, armed with acoustic recorders, genetic sequencing kits, and GPS mapping software. One of the primary questions researchers are seeking to answer is whether these two distinct lineages, which have been separated by thousands of years of divergent evolutionary cycles, can still successfully hybridize. Because the 13-year and 17-year cycles are controlled by deep genetic mechanisms, any cross-breeding could produce offspring with disrupted cycles, potentially emerging at non-prime intervals that leave them vulnerable to predation.

Furthermore, the sheer density of the insects in these overlap zones has reached staggering proportions. In some heavily forested areas, researchers recorded up to 1.5 million cicadas per acre. The physical weight of these insects has actually caused the branches of young trees to sag, while the collective volume of their mating calls has altered the behavioral patterns of local bird populations, forcing some species to alter their vocal frequencies or temporarily abandon their nesting territories.

Acoustic Warfare and the Fungal Zombie Threat

Once their exoskeletons harden and darken to a deep, jet black, the male cicadas begin their relentless quest for a mate. They produce their signature buzzing chorus using specialized organs called tymbals, located on the sides of their abdominal cavities. By rapidly contracting and relaxing the muscles attached to these ribbed membranes, the males generate a high-pitched click that is amplified by their hollow, air-filled abdomens. When millions of males sing in unison, the collective din can exceed 100 decibels—equivalent to the roar of a chainsaw or a low-flying jet.

However, this massive reproductive drive is threatened by a bizarre and gruesome pathogen: the fungus Massospora cicadina. This specialized, sexually transmitted fungus lies dormant in the soil, waiting for the cicadas to emerge. Once a nymph crawls through the spore-laden earth, the fungus infects its body, slowly consuming the insect's lower abdomen from the inside out. In place of the cicada's reproductive organs, a chalky, yellow-white plug of fungal spores develops.

Remarkably, the infected cicadas do not crawl away to die. The fungus produces psychoactive compounds, including cathinone, which keeps the insect hyperactive and highly mobile despite losing its lower body. The infected males continue to sing, but they also begin to mimic the wing-flicking behaviors of receptive females. This draws in healthy males attempting to mate, who then become infected through physical contact, turning the cicadas into active vectors that broadcast the fungal spores throughout the canopy.

Nutritional Pulses and Forest Ecosystem Reshaping

Despite the localized horrors of the fungal infection, the overall ecological impact of the emergence is overwhelmingly positive, acting as a massive, sudden injection of nutrients into the forest ecosystem. This phenomenon, known to ecologists as a "resource pulse," temporarily rewires the local food web. Predators such as wild turkeys, blue jays, squirrels, raccoons, and copperhead snakes abandon their typical diets to gorge themselves on the slow-moving, defenseless insects, a phenomenon known as predator satiation.

This abundance of easy prey has cascading effects throughout the food chain. With predators focused entirely on cicadas, other herbivorous insects, such as caterpillars, experience a temporary reprieve from predation. This, in turn, can lead to increased defoliation of forest canopies in the short term, though the trees quickly recover. Meanwhile, the nesting success of insectivorous birds skyrockets, leading to larger clutches and healthier fledglings across the region.

The final act of the cicada cycle occurs when the adults die, typically within four to six weeks of emerging. Billions of nutrient-rich carcasses rain down onto the forest floor, where they decompose rapidly. This massive pulse of nitrogen, phosphorus, and potassium fertilizes the soil, sparking a surge in microbial activity and promoting the growth of understory plants and trees. The exit holes left behind by the emerging nymphs also serve to aerate the compacted soil, allowing rainwater and oxygen to penetrate deep into the root systems, ensuring the forest remains healthy for the next generation of nymphs currently embarking on their long, silent wait.