The hollow brown ‘bug’ attached to a tree is usually a cicada’s shed outer skeleton, not a dead adult. A cicada nymph climbs out of the soil, grips a surface and splits its old exoskeleton so a winged adult can emerge. The empty casing left behind is called an exuvia (plural: exuviae).
What happens during a cicada’s final molt?
Cicadas spend much of their immature lives underground, feeding on fluids from plant roots. When ready to become adults, nymphs tunnel to the surface, climb tree trunks, fence posts or other upright surfaces, and secure their claws. The shell splits along the back. The soft new adult slowly wriggles out, expands its wings and waits while its body hardens before flying away.
Why does the insect need to leave its old skin?
An insect’s outer skeleton supports and protects its body, but it cannot stretch indefinitely. Molting lets the growing animal replace a rigid covering with a new one. Cicadas undergo several immature molts; the final one produces the recognizable winged adult. This is different from butterflies, which undergo a pupal stage during complete metamorphosis.
Does finding a shell mean there are thousands of cicadas nearby?
Not necessarily. A few annual cicadas may emerge in an ordinary summer. Certain periodical cicadas in eastern North America emerge in much larger synchronized groups in particular years and regions. An empty shell only proves that at least one nymph molted there; the number of shells and timing are more informative than one specimen.
Is the shell dangerous or alive?
An abandoned exuvia cannot bite or sting. Its little hooked claws may feel prickly, and it can be fragile. Children can observe one carefully, but should wash their hands after handling outdoor insects or shells. Avoid touching a newly emerged pale adult: its soft body and wings are easily damaged while they harden.
A simple family observation
In warm months, look on lower tree trunks near lawns or woodland edges. Photograph a shell from the side and back. Can you find the split where the adult emerged? You can sketch the front claws used to cling to bark. Leave living cicadas undisturbed, especially if their wings are still expanding.
Frequently asked questions
Why is the empty shell still attached to the tree?
The nymph’s strong claws gripped the bark before molting, and the abandoned casing may stay hooked in place until wind or rain knocks it free.
Do cicadas bite after they emerge?
Cicadas aren’t predators and do not have biting jaws designed to attack people. Their mouthparts are adapted to drink plant fluids.
Are cicada shells a sign a tree is dying?
Finding shells alone is not a diagnosis of tree damage. Many healthy trees have cicadas nearby during emergence.
For more insect behavior, read why moths circle artificial lights and how honey bees carry pollen.
Background: Mississippi State University Extension’s guide to cicada exuviae.
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