Smologies #43: CICADAS with Gene Kritsky

Episode Summary

Executive Summary: This Smologies episode explores periodical cicadas with entomologist Dr. Gene Kritsky, explaining their 13- and 17-year life cycles, synchronized mass emergence, mating calls, egg-laying, underground development, and how climate change may shift timing. It also highlights citizen science via the Cicada Safari app and concerns about brood declines and local extinctions.

Main Topics: What cicadas are and why they matter (Priority: 5/5): Allie Ward introduces cicadas as a long-awaited topic, framing periodical cicadas as rare, dramatic insects that emerge in enormous numbers and attract public fascination. Periodical vs. annual cicadas (Priority: 5/5): Kritsky distinguishes smaller, red-eyed periodical cicadas from larger annual cicadas, emphasizing that periodicals emerge in synchronized broods while annuals appear every year in smaller numbers. Emergence, molting, and mating behavior (Priority: 5/5): The episode details how nymphs emerge after soil warms and rain saturates the ground, climb vertical surfaces, shed their skins, and males begin calling to attract females. Life cycle underground (Priority: 5/5): After females lay eggs in twigs, hatchlings fall to the ground, burrow quickly, and feed on xylem for years while remaining mostly stationary below the surface. Sound, anatomy, and reproduction (Priority: 4/5): The conversation explains cicada calls, the timbals that create sound, and the female ovipositor that cuts into wood to place eggs in slits. Climate change, brood timing, and new populations (Priority: 5/5): Kritsky describes how warmer springs and unusual leaf-out events may alter cicada timing, causing some populations to emerge early and potentially form new broods. Citizen science and conservation (Priority: 4/5): The Cicada Safari app is promoted as a way for the public to document cicada sightings and help researchers map brood distributions and possible declines.

Key Arguments: Periodical cicadas emerge in massive synchronized broods as a predator-satiation strategy, making it harder for birds and other predators to consume them all. Annual cicadas are not the same as periodical cicadas; they are larger, less conspicuous, and appear every year in much smaller numbers. Cicadas know when to emerge partly by sensing soil temperature and changes in tree fluid flow, but scientists still do not fully know how they track the passage of years. Their long life cycles likely evolved in response to climatic history, including ice ages, with 13-year and 17-year forms adapting to different regions. Climate change may disrupt timing by altering spring temperatures and plant phenology, leading some cicadas to emerge off-cycle. Some early-emerging cicadas may not reproduce, but surviving off-cycle populations can seed new broods over time. Brood declines and possible extinctions are a real concern, making mapping and reporting sightings scientifically valuable. The Cicada Safari app allows ordinary people to contribute to research by photographing and geotagging cicada sightings.

Data Points: Periodical cicada cycle lengths: 13 years and 17 years - The two main life-cycle lengths discussed for periodical cicadas. Soil temperature for emergence: 64°F - Cicadas begin emerging when soil temperature reaches this threshold. Peak density observed: 356 per square yard - Kritsky’s highest observed emergence density over about two weeks. Male call loudness: 96 decibels - Highest measured loudness mentioned for one species’ call. Maximum call loudness cited: up to 120 decibels - A cited upper range for some cicada calls, compared to an ambulance siren. Egg hatch time: 6 to 8 weeks - How long after egg-laying the eggs begin to hatch. Egg count per nest: 10 to 20 eggs - Number laid in each egg nest by a female cicada. Underground depth by New Year’s Day: 10 to 12 inches below the surface - Observed depth of nymphs feeding on roots in winter. Recent climate shift in Cincinnati spring timing: About 2 weeks warmer than the first half of the 20th century - Used to illustrate how warming may affect emergence timing. Local early-emergence sites recorded: 33 locations - Locations where offspring from an early emergence were later observed on time. Historical brood extinction example: Brood 11 extinct in 1954 - Example of a brood disappearing regionally or entirely. Brood 10 concern year: 1919 - Newspaper headlines reportedly warned Brood 10 might be going extinct.

Pivotal Quotes: "They come out of the soil when the soil temperature reaches 64 degrees Fahrenheit." — Dr. Gene Kritsky: Explaining the environmental trigger for emergence. "The analogy I like to use is imagine walking outside and all of a sudden you see the whole world is inundated with flying Hershey's kisses." — Dr. Gene Kritsky: Describing predator satiation and overwhelming numbers. "That vanguard there is going to give their lives so that others can live." — Allie Ward: Commenting on early-emerging males being highly vulnerable to predators.

Implications: Cicadas are a vivid example of climate-sensitive wildlife. Public reporting through apps can aid science, while warming trends and brood instability may reshape where and when future emergences happen.