XIX

• From late April through June 2024, the largest brood of 13-year cicadas, known as Brood XIX, will co-emerge with a midwestern brood of 17-year cicadas, Brood XIII.
• A co-emergence like this of two specific broods with different life cycles happens only once every 221 years.
• For about four weeks, scattered wooded and suburban areas will ring with cicadas’ distinctive whistling, buzzing and chirping mating calls.
• Once the eggs hatch, new cicada nymphs will fall from the trees and burrow back underground, starting the cycle again.
• It’s no accident that the scientific name for periodical 13- and 17-year cicadas is Magicicada, shortened from “magic cicada.”

Ancient visitors

• Molecular analysis has shown that about 4 million years ago, the ancestor of the current Magicicada species split into two lineages.
• The resulting three lineages are the basis of the modern periodical cicada species groups, Decim, Cassini and Decula.
• The sudden appearance of so many insects reminded them of biblical plagues of locusts, which are a type of grasshopper.
• During the 19th century, notable entomologists such as Benjamin Walsh, C.V. Riley and Charles Marlatt worked out the astonishing biology of periodical cicadas.

Acting in unison

• This increases their chances of accomplishing their key mission aboveground: finding mates.
• While periodical cicadas largely come out on schedule every 17 or 13 years, often a small group emerges four years early or late.
• Early-emerging cicadas may be faster-growing individuals that had access to abundant food, and the laggards may be individuals that subsisted with less.

Will climate change shift Magicicada clocks?

• As glaciers retreated from what is now the U.S. some 10,000 to 20,000 years ago, periodical cicadas filled eastern forests.
• Today there are 12 broods of 17-year periodical cicadas in northeastern deciduous forests, where trees drop leaves in winter.
• Because periodical cicadas are sensitive to climate, the patterns of their broods and species reflect climatic shifts.
• Although periodical cicadas prefer forest edges and thrive in suburban areas, they cannot survive deforestation or reproduce successfully in areas without trees.

• In the late 19th century, one Brood (XXI) disappeared from north Florida and Georgia.
• Climate change could also have farther-reaching effects.
• As the U.S. climate warms, longer growing seasons may provide a larger food supply.
• This may eventually change more 17-year cicadas into 13-year cicadas, just as past warming altered Magicicada neotredecim.
• We hypothesize that this was due to climate warming.

John Cooley receives funding from the National Science Foundation and the National Geographic Society. Chris Simon has received funding from the National Science Foundation, the Fulbright Foundation, the National Geographic Society and the New Zealand Marsden Fund.