Faulty Eclosion in Crowded Suburban Periodical Cicadas: Populations Out of Control

A complete count of exuviae from a yard of °0.1 ha revealed 158,054 emerging periodical cicadas (Magicicada cassini) of which 31% died from faulty eclosion. Mutual interference and/or delay owing to a shortage of vertical perching places appears to be responsible, rather than poor nutrition. We argue that cicadas feeding underground are protected from predation and that they must have a long developmental period because they feed on dilute xylem fluids. The long synchronous life cycle allows Magicicada to escape predatory control by any but a synchronized enemy, and only one of these exists–a fungus disease, Massospora cicadina. In man—disturbed habitats, even this fungus is absent initially, so the cicada population increases until limited by the only remaining factor possible–space for feeding sites. Nearest—neighbor analysis indicates mutual repulsion, i.e., feeding cells were disturbed significantly more uniformly than random expectation. Emergence burrows from previous generations had filled with soil, but these "fossil burrows" were surrounded by soil crevices and not invaded by plant roots; hence, they decrease the amount of space available by for feeding sites. Apparently, periodical cicada nymphs in certain parts of some suburban lawns do indeed occupy all the feeding space available to them, yet the herbivory can be sustained by the trees.