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Sunday, June 12, 2011

Urban Wildlife Watch: 13 Year Cicadas

Cicadas, sometimes called locusts or katydids, seem to be everywhere right now. Here in my part of the country - St. Louis, Missouri and as far away as Nashville, Tennessee - the flying insects seem to be everywhere. And the numbers of them seem to be in biblical proportions. That's not a mistake or judgement day occurance, it's simply Mother Nature at play. The ones that we are witnessing right now are called 13 year Cicadas. Scientific name Magicicada.

 from Bungalow Bill's Blogspot

Coming from the south, I have always been familiar with Cicadas, in fact I think fondly of them. That characteristic an an an sound from the trees actually lulls me asleep on warm humid nights. However, I never actually laid eyes on a cicada until last year. I had only heard them! There are thousands of species of cicadas that live all over the world. But this year, we are seeing a whole lot of these:
 from Bates County Live

These 13 year cicadas are about an inch and half long with dark brown bodies with orange coloring and red eyes. Despite their annoyance, they are not harmful. They don't bite or sting; and I have heard some people say they don't have mouth parts or eat. (But I need to get an up close look at these guys to see if that part may be true. Look out for a blog post about dissecting a cicada.) So other than just being a pest, they really aren't a problem for people or pets. As to your plants, that's another story. Cicadas feed on the juices from plants, as well as lay their eggs in the bark of trees.

Overview of a cicada life cycle
from Enchanted Learning
Adults emerge in the summer and life approximately 6-8 weeks. The tend to be found in wooded areas and perched in trees and chorus on hot summer days and nights. They mate during this time and all adults by the end of summer.

Eggs are laid by the females in brood patches of up to 20 eggs or so in the bark of trees. Incubation can last 6-8 weeks. When they are hatched tiny nymphs emerge and drop to the ground.

Nymphs burrow holes in the ground (near the tree where they were 'born' and live the majority of their lives underground as juveniles no wings) http://en.wikipedia.org/wiki/Nymph_(biology). Nymphs live in the soil eating tree root juice or sap, before finally emerging to the world above. Depending on their species, they remain underground 3, 4, 7, 13, or 17 years (periodical cicadas) or one year (annual cicadas) to feed on juices from roots of plants and trees. Once they are mature, they burrow to the surface and leave distinctive holes in the soil (about the diameter of a fat pencil or dime) often near trees, bushes and other tall green vegetation. The nymphs then hold on tight to a leaf or stem or tree tunk and begin its final metamorphosis into an adult cicada with fancy wings. The shell or exoskeleton of the nymph is left behind and serves as a great indicator of the abundance of cicadas in a particular area. (pic)


To answer some questions posed by others already:
Why are there so many of them all at the same time? 13 year Cicadas are what biologists referr to as a developmentally synchronized species. They all emerge at the same time and time their activity together. Right now, we are witnessing the finally stage in the life cycle of this cicada – the adult stage when they mate, lay eggs (the next generation) and soon die. This timing is actually benefical to them. With so many coming out at the same time they actually overwhelm predators such as birds, wasps, and praying mantises. With so many cicadas available the predators get plenty of food and there are still plenty of cicadas left to mate and continue the species.

Why do they make so much noise? That distinctive sound is the mating chorus of male cicadas announcing they are available for mating. So, that's their mating call we hear. Males perch in trees and chorus together in a rhythmic sound to attract females for mating. There are other calls for courtship as well as for distress - as when attacked by a wasp or praying mantis - but most people are not familiar with those sounds. I certainly am not.

Where does the sound come from? The sound comes from vibrations of tiny membranes lining the outside of the abdomen or belly of males. Males perch in trees and chorus together in a rhythmic sound to attract females for mating. There are other calls for courtship as well as for distress - as when attacked by a wasp or praying mantis - but most people are not familiar with those sounds. I certainly am not.

It seems like they make more noise when it's hot and sunny outside, does the weather condition have anything to do with how loud they are? Yes, the amount of noise they make seems to correspond with the temperature. For example, Saturday, June 11th was an overcast day and it was considerably cooler than it was earlier this week. Some people noticed that the cicadas in their yards and nearby parks were not as noisy yesterday compared to how they sounded before when it was very hot outside. The thinking is that it has to do with body temperature regulation. When it is cooler outside, the insects spend more energy staying warm and less on singing. It may also have something to do with sound traveling faster in warm air.

Those bugs are really annoying. They fly in my face, in my car, make a lot of noise and get everywhere. What good are they? As nymphs, cicada live underground and dig through the soil. This aerates the soil to benefit plants. Although we don't know very much about their behavior at this stage, I am pretty sure that nymphs are food for underground insect predators like moles and shrews, plus they are an important part of the food chain above ground for many animals.

1 comment:

Calder Kamin said...

Hi Danielle,

I heard you on KC Currents, and I'm very interested in what you are doing. My background is in art. I too have always marveled at the animal world. My work illustrates investigations in science and cultural constructions of what is nature. I've always appreciate the ecosystems with in a city. For the last two years I've been keeping a blog on my experiences with urban wildlife, animallog.wordpress.com. Hope you can visit. I am always looking for opportunities to collaborate.
Sincerely,
Calder Kamin

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