The emergence of cicadas in Missouri signals a remarkable natural event that unfolds with precise timing beneath the cover of darkness. These insects spend the majority of their lives underground, feeding on sap from tree roots, before synchronously rising to the surface when specific environmental conditions align. For residents and nature enthusiasts across the state, understanding the schedule of these periodic emergences transforms a potentially startling occurrence into a fascinating ecological spectacle.
Primary Cicada Emergence Periods
Missouri hosts two distinct types of cicadas, each with its own predictable lifecycle. The most anticipated event involves the periodical cicadas, which emerge in massive numbers every 13 years in southern regions or every 17 years in the northern parts of the state. These insects are not annual pests; their synchronized arrival is a rare phenomenon that creates a significant biological event. Annual cicadas, which appear every summer, provide a more constant background presence but lack the collective drama of their periodical cousins.
Environmental Triggers for Emergence
While the internal clocks of cicadas are calibrated to specific year counts, the actual trigger to leave the soil relies heavily on external conditions. Soil temperature plays the most critical role, requiring the ground to reach a consistent 64 degrees Fahrenheit at root level. Adequate soil moisture and the presence of tree roots for feeding are also essential. Rain often softens the earth, allowing the nymphs to tunnel to the surface, typically in the late evening or night to avoid predators and the harsh heat of the day.
Soil Temperature and Timing
The timing of the cicada emergence in Missouri is rarely a fixed date on the calendar but rather a moving target dictated by the weather. A warm spring can accelerate the process, causing nymphs to ascend weeks earlier than in cooler years. Conversely, a prolonged cold snap can delay the event. Observers in cities like St. Louis or Kansas City might notice the first signs of activity when daytime temperatures begin to stabilize in the mid-60s, particularly following a period of wet weather.
Regional Variations Across the State
Geography significantly influences when cicadas become visible across Missouri's diverse landscape. The southern counties, closer to the Gulf Coast, generally experience warmer soil temperatures sooner, leading to earlier emergences of the 13-year cycle. The northern regions, with their longer winters, see the 17-year broods emerge later in the season. This creates a staggered biological timeline that ensures the species' survival across different climatic zones.
Mapping the 17-Year Brood
Entomologists track specific broods, or groups of periodical cicadas, that occupy distinct geographic areas. In Missouri, the emergence of Brood XIX, which includes parts of southern Missouri, is a major event that occurs more frequently than the 17-year cycle. Understanding which brood occupies a specific county helps residents predict the intensity and timing of the noise, shed skins, and brief adult lifespan that follows the initial emergence.
The Adult Phase and Lifecycle
Once above ground, the cicadas' primary mission is reproduction. Males generate a loud, rhythmic buzzing to attract females, a sound that can reach overwhelming decibel levels in dense populations. After mating, females lay their eggs in small slits cut into tree branches. This phase lasts only four to six weeks, after which the adult insects die. The newly hatched nymphs then fall to the ground and burrow underground to begin the long subterranean feeding cycle that will repeat the emergence decades later.
