A periodical cicada (Magicicada sp.) molts on the side of a tree after emerging from underground.

A periodical cicada (left) has mostly freed itself from its old exoskeleton (right). The cicada's new exoskeleton is light in color and has not yet hardened. Every 13 or 17 years, periodical cicadas (Magicicada sp.) emerge from underground burrows across several regions of North America over a few weeks. The cicadas molt to adulthood and then congregate in trees, where they sing and mate, lay eggs, and die. Densities of adult cicadas aboveground during the mass emergence can become higher than 300 individuals per square meter. Because such a large number of cicadas are available as prey over a short period of time (a resource pulse), cicada predators become satiated. Most cicadas die without being eaten and fall as detritus from the trees onto the soil or water underneath. A recent study found that this allochthonous subsidy (moving from one ecosystem to another) of cicada detritus can affect the dynamics and stability of food webs in aquatic woodland ecosystems. This photograph originally appeared on the cover of Ecology (88:9) in September of 2007.