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Tales from a Plant Addict



The question on everyone's mind lately seems to be "Are we going to get the cicadas this year?" Unless you've purposefully avoided the news lately, you know that this question refers to what's happening in Northern Illinois, particularly the Chicago area. This part of Illinois is in the midst of the emergence of the 17-year cicada.

These 17-year cicadas are not the same species as the "dogday" cicadas that emerge in July and August, the "dogdays" of summer. The many species of dogday cicadas we see each year are members of the genus Tibicen and they have life cycles of two to five years. If you catch one later this summer, they are stout insects about an inch to an inch and a half long and about half an inch wide. Their wings are transparent with heavy black veins and their bodies look like someone painted them in a traditional camouflage pattern.

The cicadas that are getting all the attention recently are of the genus Magicicada, and have life cycles of 13 or 17 years. While they are about the same size, they look distinctly different than the dogday cicadas. Their bodies are dark brown to black, have distinct orange veins on their wings, and bright red eyes. There's no mistaking them for a dogday cicada.

Fortunately for those of us that want to know when "they" are coming, entomologists are fascinated with the extended life cycle of the 13 and 17-year, also called periodical cicadas.

There is some debate on how many species of cicada actually have 13 or 17 year life cycles. Some argue that the same three species emerge on either a 13 or 17 year interval. At the other extreme, some entomologists insist there are six individual species, three with a 13 and three with a 17 year life span. Many experts opinions lie somewhere in the middle. Nonetheless, the fact remains that these insects with distinctly extended life cycles are distributed east of the Rocky Mountains in North America, but occur nowhere else in the world among the over 2,500 species of cicadas.

In 1907, an entomologist working for the U.S. government named C.L. Marlatt published details on the emergence of cicadas, which seemed to emerge in groups, also called broods in entomologist lingo. He originally identified 30 broods, assigning each a Roman numeral. These designations are still in use today, although now scientists believe there to be 15 broods, and not 30.

Back in 1975, an Illinois Natural History Survey entomologist, Lewis Stannard, Jr. published The Distribution of Periodical Cicadas in Illinois. Stannard described the five broods that exist in Illinois, and most importantly mapped them.

The brood that everyone is so excited about right now is the Northern Illinois Brood, also called Brood XIII. This brood emerges at 17 year intervals and is expected to emerge across most of Illinois over the next few weeks. Parts of Iowa, Indiana, Michigan and Wisconsin are also in sync with this brood. The counties closest to Macon County that are potentially affected are Logan and McLean counties.

Macon County houses Brood XIX, or the Great Southern Brood. These periodical cicadas have a 13 year life cycle. The last emergence was in 1998, so Macon County can expect to see another round of cicadas in 2011.

The third brood in the Macon County area is Brood III, or the Iowan Brood, composed of 17-year cicadas. It covers a relatively small area in DeWitt, Piatt and Champaign counties. This small area appears to have been broken off from the larger brood area that occurs in western Illinois, Iowa and Missouri. We won't see these again until 2014.

Of course, another reason people are fascinated with the 13 and 17-year periodic cicadas is their tendency to emerge in very large numbers, particularly in areas with lots of established trees, which the nymphs, or immature cicadas, feed on underground through the roots in the years prior to their emergence.

It's not unusual to see the ground covered solidly in periodic cicadas in areas which have been undisturbed, like old neighborhoods or wooded areas. During the last emergence of periodic cicadas in Northern Illinois, where I'm from, I remember staff at our local swimming pool scooping cicadas out of the pool each morning by the net full, and sweeping them into enormous piles with big push brooms on the pool deck and grounds. It seemed like every available surface was covered with them.

I remember that just about everywhere you looked there was either an adult cicada or the vacant shell of an emerged cicada nymph. Every single one of the cicadas clogging the local pool, our driveway, our windows, falling on us, getting crunched under our feet or eaten by the dog had at one time lived underground peacefully feeding on sap from a tree root for the previous 17 years.

When their 17 years were up they started burrowing for the surface, then searched desperately for anything to climb as high as they could on. As if by magic the shell of each nymph split and the devil-red-eyed adults emerged and began their mission for their short-lived five or six week adult stage: finding a mate, mating, laying eggs, and eating a little. They do have piercing mouthparts and will feed on woody plants, but typically do not create significant damage by feeding.

One common misconception that people have about the cicadas is that they are locusts and they will consume all vegetation in their path. This is not the case. Locusts and cicadas are entirely different animals. Locusts are a type of grasshopper, and cicadas are entirely different. They lead a very unique lifestyle.

The real potential for damage caused by cicadas is in egg laying. The female cuts a slit into the bark of small trees and shrubs with a sickle-like projection on her abdomen and deposits her eggs. In some cases, small twigs will have so many slits cut into them that they die, a phenomenon called flagging. On most trees this is not a big deal. If the tree is very young and small, this can be deadly. The only way to avoid the damage to young trees is to cover them with screening to exclude the cicadas. Or another alternative is to not plant small trees immediately prior to a periodic cicada emergence.

When the eggs hatch, the young cicada nymphs drop to the ground and quickly burrow up to two feet underground, where they find a nice tree root and spend the next 13 or 17 years feeding from it. This typically does not harm the tree.

I read in the local paper from my hometown that a popular park is preparing for the cicadas by having microphones available for all events that they host, such as weddings. They expect cicadas in numbers high enough that their "singing" will necessitate microphones if you want any hope of being heard.

The song of the cicada is produced only by the male and is unique to each species. This singing is how individuals locate mates and sound alarms when danger approaches. Unlike other insects that make sound by rubbing body parts together, like crickets, cicadas have what is essentially a built in drum set.

The source of a cicada's song are structures called tymbals, one on each side of the abdomen. They are hollow membrane covered chambers that the cicada vibrates with powerful abdominal muscles to produce sound. A cicada's song is one of the loudest insect-generated sounds on earth.

Scientists have many hypotheses as to why the periodic cicada has evolved such a long life cycle, but one of the more popular ones is that the long life cycle helps avoid predation. Any predator that happens upon a periodic cicada emergence certainly leaves with a full belly, but if he comes back to that same spot the next year there will not be a meal waiting. This means that the next time the periodic cicadas emerge, there probably won't be predators lined up ready to eat them as soon as they come out of the ground.

In many parts of the world cicadas are a part of the human diet. In the U.S. it seems to be mostly an "I double dog dare ya" phenomenon rather than a source of nutrition. I've already seen a few news stories from the Chicago area interviewing someone crunching on a cicada. I've even seen some recipes for cooking them. People that have eaten them say they taste like almonds. You may be brave enough to see if they're right. Personally, I'll take their word for it.

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