Cicadas are fascinating insects primarily recognized for their loud summer songs. Most of their lives, however, are spent out of sight, beneath the ground as nymphs. This subterranean phase is crucial for their development and eventual emergence as adults.
Life Underground
After hatching from eggs laid in tree branches, tiny cicada nymphs drop to the ground and immediately burrow into the soil. Once settled, they begin feeding on the watery sap, known as xylem, from tree roots. Nymphs use specialized straw-like mouthparts to extract nutrients. This underground period can last from two to 17 years, depending on the species. Periodical cicadas are known for their synchronized emergences after 13 or 17 years, while annual cicadas have life cycles of varying lengths but emerge yearly due to unsynchronized development.
How Deep They Go
Cicada nymphs typically burrow to depths where they can access tree roots. Most are found at depths ranging from approximately 6 to 24 inches (15 to 60 cm). Periodical cicada nymphs, for instance, are commonly found in small underground chambers about 8 to 12 inches below the soil surface beneath their host trees. As they grow, nymphs may adjust their depth, moving deeper to find larger roots or closer to the surface as their emergence approaches.
What Affects Burrowing Depth
Several environmental factors influence how deep cicada nymphs burrow. Soil type plays a significant role; they often prefer sandy or loamy soils, which are easier to move through. Soil moisture levels also affect their depth, as nymphs seek stable conditions, avoiding soil that is too dry or waterlogged.
Temperature is another factor, with nymphs seeking consistent temperatures underground, as drastic changes can be detrimental. The availability and depth of suitable tree roots for feeding directly dictate where nymphs establish their chambers. These factors can lead to variations in burrowing depth even among cicadas of the same species in different locations.
The Ascent to the Surface
After completing their nymphal development, cicadas prepare for their final ascent. They dig tunnels upward, creating exit holes to the surface, sometimes constructing mud turrets in wet areas to prevent holes from filling with water. The trigger for their emergence is often specific soil temperature; for many periodical cicadas, this occurs when the soil at a depth of 8 to 18 inches reaches approximately 64 degrees Fahrenheit (18 degrees Celsius). Once conditions are right, nymphs emerge from the ground, often in the evening, and climb onto nearby vertical surfaces like trees or plants for their final molt into winged adults.