The Sounds of Summer

I was in the park one evening last week when I heard the cicadas sing for the first time this season. I love this time of the year, if only for the cicadas and their song. It's free entertainment in the parks, neighborhoods and your backyard. I will often hang out on the patio during the evening to listen to their metallic buzz that builds up in volume until it gradually softens and dies out, only to repeat the chorus again. I find most insects interesting, and the cicadas are no exception.

Let's start at the beginning of the cicada's life cycle.  After mating, the female will make a long slit in a young twig and deposit her eggs.  These slits will often kill the affected twigs, especially oak and hickory trees. If you look carefully, you can find where the females have been actively laying eggs. There will usually be small clusters of brown leaves (especially on the lower part of a tree) among the healthier, green leaves of a tree.

Cicadas undergo simple metamorphosis. After hatching, the young nymphs fall to the ground, burrowing under the ground to feed on sap from tree roots. Nymphs can live up to 20 years, depending on the species and food availability. Periodical cicadas have life cycles of either 13 or 17 years. When the nymphs mature (from Mid-May through July), they tunnel up from underground and crawl onto the trunks of trees or other surfaces. You can look for their emergence holes around tall trees. These holes are about the size of a pinky and there is no excavated soil around the holes.

The new adults will split from their old exoskeletons and emerge in their new bodies. The adults appear white because their new exoskeletons are soft. It takes several hours for the exoskeleton to harden and the adults to gain their characteristic colors.

After emerging, the adults begin to pump their wings up with blood in preparation to fly to the trees. The males begin singing soon after emergence and both sexes only live 5 to 6 weeks.

A cicada's body is made for singing. The adult male cicada possesses two ribbed membranes called tymbals, (think of drums) one on each side of its first abdominal segment. By contracting the tymbal muscle, the membrane collapses inward, producing a loud click. As the membrane snaps back, it clicks again. These muscles rapidly pull the tymbals in and out of shape and the sound is intensified by the cicada's mostly hollow abdomen. The vibrations travel through the body back to the tympani, which further strengthens their song. The male sings to attract a a female, or to socialize with their fellow cicadas.  Each Cicada species sings during a certain time of the day and in its own habitat. Some species only sing while perched on a certain type of plant. 

As a side note, it has been found that cicadas think the sounds made by power tools and lawn maintenance equipment are made by their fellow species. They get confused and will land on the people using the equipment! If this bothers you, cut your lawn in the early morning or near dusk when the cicadas are less active. 

Cicadas also have ways of protecting themselves from predators. Some cicadas will briefly sing from one perch before moving on to a different location. Many Cicada species have colors that blend in with their surroundings, known as camouflage. Singing at dusk makes it difficult for predators that hunt by sight. Other species have bright colors, such as red, that alert predators they are poisonous when ingested (Monarch Butterflies also display the same warning colors). There is also safety in numbers; a multitude of singing cicadas make it nearly impossible for a predator to single out one insect, and even the volume of the chorus can scare the predator away.

There are over 75 cicada species in North American.Two common cicada species in Missouri are the Dog-Day, or Annual Cicadas (Tibicen spp), and the Periodical Cicadas. Dog-day cicadas are larger than periodical cicadas. They are blackish in color and their wings have a greenish edging. Their life cycle lasts from two to five years, but because of overlapping generations, some adults appear every year (usually July through September).

Periodical Cidada. Picture taken in 2011.

The last Periodical Cicada outbreak was in the Summer of 2011

Other cicadas found in Missouri include:   

    Cicadetta calliope
    Neocicada hieroglyphica
    Tibicen pruinosus 
    Tibicen superbus    
Take pause next time you're outside and listen to the summer song of the Cicadas. What beautiful music these insects create. 

Glossary:

Exoskeleton: Skeletal structure formed on the external surface of insects.

Nymph: Immature stage of an insect with simple metamorphosis

Predator: Animal that moves and hunts smaller animals

Simple Metamorphosis: Pattern of metamorphosis that involves eggs, followed by immature nymphs, and finally adults.