Last week while visiting cicada land just a few miles south of Washington DC, I was greeted by an eerie silence quite unlike the boisterous chorusing of male cicadas that rocked the treetops just a few weeks ago. The reason for the silence was immediately apparent. Of eighty cicadas I encountered, only four were noisy males. The remaining throng consisted of mute females with abdomens shrunken after having deposited all but the last of their eggs in the treetops. Beneath the trees and shrubs, the ground was littered with thousands of decomposing exuviae, the shed skins of cicada nymphs, and the bodies of adult cicadas that had survived the onslaught of hungry foxes, squirrels, blue jays, robins, and other predators that feasted on them during this season of bounty. Scattered about were also the wings and fragmented body parts of cicadas that were not so lucky. What, then, is the legacy of Brood II?
Despite the onslaught of predators and nasty pathogens like Massospora we met in the last episode of Bug of the Week, scientists believe that in most cases a majority of cicadas best their enemies and complete their biological imperative to mate and reproduce. Gaging from populations I visited from North Carolina to New Jersey, it appeared that cicadas were having a banner year. For many predatory birds, the years that periodical cicadas are present are marked by the production of more and healthier young with better chances of survival. Some mammals, such as shrews, may also enjoy enhanced reproduction in the year of cicada emergence.
For trees and shrubs in the forests of cicada land, the periodical cicadas have been a mixed blessing. Vast numbers of nymphs removing xylem fluid for 17 years underground certainly placed a burden on their host trees. We also learned that the egg-laying behaviors of the females could extract a toll on woody plants in the form of branch damage and dieback in the episode entitled “Brood II up in Maryland, Magicicada spp.” However, we now know the decomposing remains of cicadas provide an enormous boost in the microbial community beneath trees. In turn, this bloom increases the availability of nitrogen in the soil which can enhance growth and reproduction of other sylvan plants. In addition to these benefits, one can only marvel at the service cicadas provide with respect to aerating the soil beneath trees. Many locations sported upward of 40 pencil-sized holes more than 10 inches deep per square foot in the earth beneath cicada trees. These conduits for infiltrating water often remain open for more than a year.
For humans up and down the east coast, periodical cicadas again provided millions of Americans with an opportunity to witness the spectacle and mystery of one of Mother Nature’s most awesome events - survival against enormous odds, courtship in the treetops, cicada sex, birth, and death all in one’s back yard. So, adieu Brood II - see you again in 2030. But for those like me who might not want to wait quite that long, plan on heading to Iowa and Illinois for the appearance of the great Iowan Brood, Brood III, in 2014.
Just south of Washington, D.C. the boisterous choruses of cicadas have ended.
The wonderful articles by K. S. Williams and C. Simon “The ecology, behavior, and evolution of periodical cicadas” and “Periodical Cicadas as Resource Pulses in North American Forests” by Louie H. Yang were used as a resources for this episode.
To view other recent episodes of Bug of the Week that explore Brood II, and other excellent websites dedicated to cicadas, please click on the following links: