Behind the Forecast: Cicadas: Could cool weather delay their emergence

LOUISVILLE, Ky. (WAVE) - They are coming! Cicadas are getting ready to creep out of the ground en masse. While it sounds like the beginning of a horror movie, it’s something that we have to deal with every 13 to 17 years. Weather does play a role in when cicadas emerge.

There are annual and periodical cicadas. Annual cicadas are larger and look slightly different from periodical cicadas. Annual cicadas come up each year, are larger than periodical with greenish wings, and emerge from July to September, according to the PennState Extension.

Adult periodical cicadas are about an inch and a half long, black with red-orange eyes and wing veins. They emerge from late May through early June. There are seven known species of North American periodical cicadas including the 13-year and 17-year cycle species. The 2021 emergence is expected to contain all three 17-year species. They are a part of Brood X, which is one of the largest United States cicada groups, according to University of Kentucky experts. The cicadas will be seen in Kentucky, especially along the Ohio River, and Indiana, especially in south-central Indiana. The cicadas are also expected in Michigan, Illinois, Ohio, New York, Tennessee, North Carolina, Georgia, West Virginia, Virginia, Maryland, Pennsylvania, Delaware, and New Jersey.

Temperature, specifically soil temperature, influences when periodical cicadas emerge. Rain, air temperature, and direct sunlight help to warm the soil. Studies have found that cicadas emerge when ground temperatures 8 inches below the ground reach 64°F. Rain also plays a role, according to some experts. Warming Spring temperatures are thought to be the catalyst for emergence with rainfall the final trigger to warm up the soil more as it seeps into the ground.

Experts say that rain on an 80° or warmer degree day, will help to warm the ground enough to trigger emergence. Multiple weeks of highs in the 70s are also said to help with brood emergence.

A changing climate can influence the life cycle of these animals. Overall, Kentucky is trending warmer and wetter. Data from the National Climatic Data Center comparing 1971 to 2000 climate normals to 1981 to 2010, showed that Louisville’s average temperature rose by half a degree. The city’s average precipitation increased by 0.24″. Weather changes could lead to different parts of broods emerging earlier, or sometimes later.

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