In defense of cicadas and forgotten entomologists

    In most places on earth, Cicadas are valued as a food source for a huge number of species, including humans.

    They are slow flyers with no stingers or biting mouth parts. They’re also much bigger than most other plentiful bugs- probably just about the easiest protein to collect and process.

    If these insects are so favored as food by other species, why doesn’t the population get wiped out? Well, some of the many types of cicadas have developed a elegant, if passive, defensive adaptation that protects them from being completely annihilated by predators.

    Periodic cicadas emerge from the ground all at once every thirteen or seventeen years. It is thought that they have the longest adolescence of any insect on earth. Scientists still don’t understood how giant broods, covering acres or even miles, know the exact moment to emerge into daylight, but they do. When this mass emergence takes place, species that feed on cicadas win the food lottery. In these years, birds lay more eggs, and more of their fledglings succeed. The name for this phenomenon is predator satiation, where the environment is so full of a prey species that the predators simply cannot eat them all.

    But because the cicadas have such a long life cycle, predators can’t become dependent on them as a regular food source. That ballooning bird population will be long gone by the next time the cicadas emerge. And if you want to get all DaVinci Code here, you’ll observe that 13 and 17 are prime numbers, meaning that the two cycles will hardly ever overlap, keeping the two populations distinct.

    Since cicadas suck the juices out of roots, periodic emergence years can be hard on plants, especially cultivated crops. During most of the nineteenth century, when the natural populations of cicada weren’t yet withered by habitat loss, crop damage from periodic cicadas was a significant problem for farmers. It was a Northwest Philadelphian who cracked the mysterious lifecycle of the cicada, making it possible for the government to begin to manage this insect pest. Here’s the story:

    Margaretta Hare Morris came from a venerable and pedigreed Germantown family. No beauty, she lived at the family home on the corner of Germantown Ave. and High Street with her mother and sister her entire life, apparently as somewhat of a recluse. Although she never had an advanced education, she became a very well-regarded entomologist. Her explorations occurred mainly in her garden, separated by a bank of shrubbery from bustling Germantown Avenue. In 1847 it was she who first accurately predicted the emergence years of this insect.

    Like the cicadas she studied, not often did she emerge into society. But she corresponded with Charles Darwin, who was dismissive, and other famous naturalists of her day, who were less so. Eventually she became the first woman elected to the Academy of Natural Sciences, where she would hand her papers to men to be read aloud. In 1950 a biographer assessed that she would have been one of the early greats at the Academy had she been male.

    Philadelphia in the first half of the 19th century was one of the most exciting places on the planet for scientific discovery, so much progress was taking place. And a large number of the discoveries were being made by amateur observers- people like Margaretta Hare Morris, who spent a lifetime quietly watching the habits of creatures in her backyard, and made an important contribution to the development of science.

    Want a digest of WHYY’s programs, events & stories? Sign up for our weekly newsletter.

    Together we can reach 100% of WHYY’s fiscal year goal