Cicada Molting: Nature’s Astonishing Transformation Explained
Shell casts reveal each insect’s perilous journey from nymph to vulnerable winged adult.
Every 17 years, millions of cicadas emerge from the earth in a dramatic natural event that floods forests and suburbs across the eastern United States. Amid the chorus of these red-eyed insects comes another phenomenon: the sudden appearance of brown, shell-like objects clinging to tree trunks, fences, and leaves. These are cicada exoskeletons, left behind in the process known as molting—one of nature’s most fascinating transformations.
What Is a Cicada Molt?
When discussing cicada molting, experts often mention the term exoskeleton, the rigid outer covering that defines the structure and protection for many insects. Molts are the empty, shed skins of cicadas as they transition from the nymph stage to adulthood. As Dr. Nancy Troyano, Ph.D., explains, these shells are the ‘insect skin’ left behind after cicadas grow into their final, adult form.
The exoskeleton serves multiple purposes:
- Provides structural support
- Acts as a barrier against predators and environmental hazards
- Enables muscle attachment for movement
However, since this outer layer doesn’t grow with the insect, periodic shedding is necessary—a phenomenon common among all arthropods (the animal group that includes insects, spiders, and crustaceans).
Why Do Cicadas Molt?
Cicadas begin their lives as nymphs, immature versions of the adult insect, living underground for up to 17 years in the case of Brood X. During this time, they develop just below the surface, sustained by tree root sap. As they reach the end of their underground life, vital transformations occur beneath their outer skin. Specifically, cicadas are:
- Preparing internal organs for adulthood
- Developing wings beneath the nymph exoskeleton
- Expanding their bodies for their final molt
When the time comes, cicadas surface and seek a firm perch, often on tree bark or stems. The act of molting signals their shift from the nymph to the adult phase. As Dr. Angela Tucker, Ph.D., puts it, because the exoskeleton is hard and unyielding, “it prevents insects from growing so they must molt the ‘skin’ to continue to develop.” The new, larger exoskeleton forms underneath the old one and only becomes functional after the molt.
How Cicada Molting Works: A Step-by-Step Look
Experts liken the process of molting (technically termed ecdysis) to wriggling free from a suit of armor. Here’s a closer look at what actually happens:
- The nymph climbs to a safe location, such as a tree trunk or shrub.
- Internal pressure rises: The cicada pumps hemolymph (the insect equivalent of blood) and air inside its body, causing the old exoskeleton to crack along the back.
- The cicada pulls itself out: Through slow, deliberate movement, it extracts its body, head, legs, and finally its wings. The new exoskeleton emerges soft and pale.
- Wings inflate and expand, filling with fluid while muscles and veins strengthen.
- The new exoskeleton hardens: Over several hours to days, exposure to air toughens and darkens the shell.
This entire process typically takes between one to two hours, though the full hardening of the adult skin can require additional days in hiding.
Molting Vulnerability
During and just after molting, cicadas are particularly susceptible to predators such as birds, raccoons, and even other insects. Frank Meek, technical manager for Rollins pest control, notes they’re “a juicy little morsel” during this teneral (freshly molted) stage, unable to fully defend or flee. Once hardened, cicadas become more mobile and durable, ready to join the cacophony of adult life.
How Long Does the Molting Process Take?
Compared to many insects, cicada molting is a relatively slow and painstaking ordeal. The actual shedding event takes around one to two hours. However, it’s only after several days that their new exoskeletons fully harden and darken, allowing them to resume normal activity and flight. During this time, newly molted cicadas tend to hide on leaves, in branches, or high off the ground—anywhere they’re less visible and exposed to hungry predators.
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Why So Slow?
The slowness of the process is largely a product of biological necessity:
- Ensuring proper wing expansion: If wings don’t inflate and harden, the cicada will be unable to fly or survive.
- Allowing time for exoskeleton tanning: As with other arthropods, the new cuticle must ‘tan’—a process that involves darkening, drying, and hardening—for effective use.
- Reducing energy demands: The insect expends considerable energy during this period, which could be harmful if accelerated.
Molting failures can and do occur if a cicada takes too long or is disturbed. In such cases, wings may become deformed, legs trapped, or the insect left unable to move—an unfortunate but common occurrence throughout the insect world.
Why Are There So Many Cicada Shells?
In emergence years like that of Brood X, the sheer numbers of cicadas means a correspondingly massive number of molts. Each cicada undergoes this transition—a phenomenon amplified by the scale of synchronized population emergence after more than a decade underground. Annual cicadas, appearing each summer in smaller numbers, also molt their exoskeletons, but the appearance of millions at once is unique to periodical cicadas like Brood X.
- Brood X cicadas appear en masse roughly every 17 years, creating an incredible density of exoskeletons.
- Each exoskeleton is a physical record of a single nymph’s ascent to adulthood.
Finding multiple exoskeletons in a single area is a sure sign that adult cicadas are present and in full chorus nearby.
What Should You Do If You See Cicada Molts?
If you encounter cicada exoskeletons attached to your trees, porch railings, or garden plants, experts offer the following advice:
- Do not panic: Cicadas are harmless to humans and pose minimal risk to mature vegetation.
- No pesticides needed: There is no need to treat for cicadas with chemicals; they are not traditional pests and have a brief adult lifespan.
- Easy removal: If the abundance of molts is bothersome, simply spray them away from surfaces with a garden hose.
- Prevent access: To keep cicadas from crawling up valuable plants, wrap the base with mesh or cheesecloth.
As Dr. Troyano points out, the exoskeletons do not pose any threat and are quickly reclaimed into the ecosystem by weather and other animals. Frank Meek suggests simply “enjoying the wonder of nature” during cicada emergence; after all, the spectacle will only last four to six weeks before the adults die off, leaving behind another round of molted shells as testament to their time above ground.
The Exoskeleton: Marvels and Drawbacks
While the exoskeleton has obvious protective qualities, there are evolutionary trade-offs involved.
| Advantage | Drawback |
|---|---|
| Defense Against Predators | Limits Growth; Requires Molting |
| Structured Muscle Attachment | Period of Vulnerability During Molting |
| Water Retention | Risk of Malformation if Molting Fails |
Unlike vertebrates, whose bones grow with their bodies, arthropods must repeatedly shed and replace their external skeleton to grow bigger—a process that is both a marvel of nature and a dangerous gamble.
Frequently Asked Questions (FAQs) on Cicada Molting
Q: Are all cicada exoskeletons from 17-year brood cicadas?
A: No. While synchronized outbreaks like Brood X generate spectacular numbers of exoskeletons, annual cicadas also molt and leave behind their shells every year.
Q: Will cicada shells harm my trees or garden?
A: Cicada shells are harmless and do not damage trees or shrubs. Adult cicadas may damage delicate, young tree branches when laying eggs, but mature plants are unaffected.
Q: Can I touch or collect cicada exoskeletons?
A: Yes, cicada shells are dry, brittle, and completely safe to handle. Many children (and adults) find them fascinating nature keepsakes.
Q: How can I discourage cicadas from gathering in my yard?
A: To minimize cicadas on specific plants, use coverings like mesh or cheesecloth at the base. Removing shells and spraying adults with water can also reduce local numbers without harming either insects or plants.
Q: Why do some emerging cicadas fail to fly?
A: Molting failures caused by space crowding, extended emergence time, or physical defects can result in misshapen wings or trapped limbs, leaving some cicadas unable to fly or feed properly.
The Wonder of Cicada Molting
The synchronized emergence and transformation of periodical cicadas is among the most spectacular natural phenomena on the planet. Their discarded exoskeletons are tiny tombs—marks of survival during one of the most perilous passages in the insect world. For a few short weeks, the seemingly ordinary brown shells are proof of an extraordinary struggle for life, offering a tangible and awe-inspiring connection to nature’s cycles. If you witness cicada molts this season, take a moment to observe, wonder, and appreciate the extraordinary process unfolding in your backyard.
References
- https://www.prevention.com/life/a36462747/cicada-molt-exoskeleton/
- https://bygl.osu.edu/node/2016
- https://evolution.berkeley.edu/the-arthropod-story/an-evolutionary-constraint-small-size/molting-and-the-exoskeleton-a-double-edged-sword/
- https://cicadas.uconn.edu/emergence-failure/
- https://www.youtube.com/watch?v=yj8G17dessg
- https://www.youtube.com/watch?v=RklBHC-bGLo
- https://www.explorenature.org/blog/periodical-cicadas-you-cant-make-this-stuff-up/
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