Where 17-Year Periodical Cicadas Lay Eggs During Emergence

Periodical cicadas are among the most fascinating and enigmatic insects found in North America. Known for their synchronized mass emergence every 13 or 17 years, these insects captivate scientists, naturalists, and the general public alike. The 17-year periodical cicadas, in particular, have garnered much attention because of their extraordinary life cycle and distinctive behaviors, especially regarding where and how they lay their eggs during emergence. This article dives deep into the biology, ecology, and egg-laying behavior of 17-year periodical cicadas to uncover where they deposit their eggs and why this stage is critical for their survival.

Understanding the 17-Year Periodical Cicadas

The 17-year periodical cicadas belong primarily to the genus Magicicada. These species spend most of their lives underground as nymphs, feeding on the sap from tree roots. After 17 years of development beneath the soil, they undergo a remarkable synchronized emergence, transforming into winged adults that surface en masse.

This incredible periodicity has evolved as a survival mechanism to overwhelm predators through sheer numbers, a phenomenon called predator satiation. Once above ground, adult cicadas live only for about four to six weeks, during which time their primary goals are mating and laying eggs. The females’ choice of oviposition (egg-laying) sites is a critical aspect influencing the success of the next generation.

The Egg-Laying Process of 17-Year Periodical Cicadas

Timing of Egg-Laying

After emerging from the soil and undergoing their final molt into adults (a process called ecdysis), male cicadas begin their loud chorusing calls to attract females. Once mating occurs, females proceed to lay eggs by inserting them into tree branches.

Typically, egg-laying begins shortly after adults emerge and mate, often within a week, and continues throughout their brief adult lifespan. This rapid reproductive cycle ensures that eggs have enough time to develop before winter.

Selection of Oviposition Sites

Female 17-year periodical cicadas are highly selective about where they lay their eggs. They prefer specific tree species and certain parts of those trees. The choice is influenced by factors such as bark thickness, branch diameter, moisture content, and tree health.

Cicadas generally target small twigs or branches that are about pencil-thickness in diameter. These branches provide optimal conditions for egg incubation and nymph development. Thick branches or trunks are not preferred because the female’s ovipositor is more adapted for cutting into smaller stems.

Preferred Tree Species

Periodical cicadas exhibit preferences for particular host trees when laying eggs. Some common preferred hosts include:

Deciduous hardwood trees such as oaks (Quercus spp.), maples (Acer spp.), hickories (Carya spp.), ashes (Fraxinus spp.), and dogwoods (Cornus spp.).

Occasionally, they may use fruit trees like cherries (Prunus spp.) or hawthorns (Crataegus spp.).

Preference varies depending on geographic location and local availability of suitable trees.

The Oviposition Mechanics

The female uses her sharp ovipositor, a specialized egg-laying organ, to make slits or grooves in the bark of the chosen twig or branch. She then deposits rows of eggs within these slits. Each egg chamber can contain multiple eggs arranged in neat rows.

The process damages the plant tissue but generally does not kill healthy mature trees outright unless there is heavy infestation or repeated oviposition over several years.

Why Do 17-Year Periodical Cicadas Lay Eggs in Twigs?

The choice to lay eggs in twigs rather than larger branches or trunks serves several ecological and biological purposes:

Protection from Predators: Eggs inserted inside twigs gain protection from external predators such as birds and parasitic wasps.
Suitable Environment for Incubation: Twigs offer an environment with appropriate moisture levels necessary for egg survival.

Ease of Nymph Hatching: Once hatched, nymphs drop to the ground where they burrow underground near roots from which they will feed for many years.
Minimizing Damage: Although egg-laying causes some damage, twigs can often survive this minor injury better than thicker branches would tolerate repeated damage.

Impact on Host Trees

While individual egg deposits usually do not cause significant harm to mature trees, mass oviposition can lead to what is known as “flagging,” where twig tips die back due to tissue damage caused by repeated egg-laying sites.

Trees heavily infested with cicada eggs can experience noticeable dieback at branch tips during summer months following emergence. However, this damage is typically temporary and does not kill healthy trees outright.

Fruit orchards or young trees may be more vulnerable to damage during heavy emergences because the cumulative effect of many females laying eggs can weaken or stunt growth.

Lifecycle: From Egg Laying to Underground Nymph Stage

Once laid inside twigs, cicada eggs incubate for approximately six to ten weeks before hatching. After hatching:

Tiny nymphs drop from the tree canopy to the soil below.

They burrow downward seeking roots from which they will feed.
These nymphs remain underground feeding on xylem fluid from roots for up to 17 years.
After completing development underground, they tunnel back up to emerge synchronously as adults, repeating the cycle.

Geographic Distribution and Emergence Sites

The emergence range for 17-year periodical cicadas spans much of the eastern United States, from Illinois eastward through Pennsylvania and New York down into parts of Georgia and Alabama.

Emergences typically occur in wooded areas where favored host trees abound; however, isolated populations may also emerge in urban or suburban areas where suitable tree species exist.

Because female cicadas select specific twigs on host trees for egg-laying during these emergences, one often sees clusters of twig dieback during peak cicada years, especially in areas with high population densities.

Factors Influencing Egg-Laying Site Selection

Several environmental factors influence female cicada preference when choosing oviposition sites:

Twig Diameter: Preferred branches are roughly 3-8 mm thick, too thin may not support eggs well; too thick may be too tough to penetrate.
Twig Health: Healthy green twigs are preferred over dead or diseased ones since developing nymphs benefit from living tissue.

Tree Species: As mentioned earlier, local availability drives host selection.
Microclimate: Sunlight exposure and moisture levels around potential oviposition sites also affect suitability.

These preferences ensure optimal conditions for offspring survival despite short adult lifespans lasting only weeks after emergence.

Conclusion

The incredible life cycle of 17-year periodical cicadas culminates each emergence with a fascinating reproductive strategy centered around precise egg-laying behavior. Females carefully select specific hardwood tree twigs in which they create slits using their ovipositors to deposit rows of eggs. This seemingly simple act is vital for ensuring that newborn nymphs have a safe start before dropping underground for nearly two decades of subterranean development.

Understanding where these insects lay their eggs not only sheds light on a unique evolutionary adaptation but also helps inform forest management practices, particularly in areas prone to heavy cicada emergences, to minimize potential damage while appreciating one of nature’s most astonishing timed phenomena.

Whether you witness an emergence firsthand or study it scientifically, knowing about where 17-year periodical cicadas lay their eggs offers a glimpse into an extraordinary natural event shaped by millions of years of evolution.