How Cicadas Choose the Right Tree
After 17 years of patient maturation underground, periodical cicadas emerge in the millions. Their goal is to find a mate, lay eggs and die. Like a zombie horde, the cicadas crawl up tree trunks, flutter clumsily among the branches and screech a mating call nearly 100 decibels loud, about as ear-damaging as a motorcycle. While these bugs may seem mindless . . . and for the most part they are . . . cicadas are actually somewhat choosy in selecting which trees to terrorize.
While species of cicada exist all over the world, only the cicada of genus Megicicada in North America require 13 or 17 years to mature. This means that wherever the female cicada deposits her eggs, they need to be in a spot where the young nymphs will thrive for years. You think picking a daycare facility is hard, imagine choosing a single place to leave your kid at for nearly two decades! Those are some really high stakes!
So how does the discerning cicada pick the right tree? One major factor guiding cicadas is sunlight. Younger forests have less dense canopies and allow more sunlight to filter down. This kind of environment provides subtle clues about the conditions underground. Young trees have actively growing roots that cicada nymphs can happily suck on during their long maturation. They also provide a bit of insurance over older trees; they’re more likely to endure into the future. Strong light cues are why you frequently see cicadas swarming around trees lining roads, forest edges or in suburban areas when silly humans space out the trees.
A cicada mom also feed on the tree while depositing her eggs and may be able to decide over a meal if its the best tree for her young ones. This is probably why cicadas rarely lay eggs on conifers or other trees with resins or saps that could harm insect eggs. They prefer fruit trees, oaks and other hardwoods where the tough bark can protect the future brood and a sugary sweet xylem treat oozes through the roots.
So if you’re not an insect person and cicadas gave you the willies before reading this, now imagine them all as anxious mothers competing for spots in an exclusive daycare. Terrifying!
Brian Rutter, PhD, is the cofounder of Thing in a Pot Productions and a postdoctoral researcher in plant biology at Indiana University. Subscribe to our newsletter to receive our “Things About Things – Odd Facts About Plants” and video production tips in your inbox every month!
Works Cited:
Clay, Keith, Angela L. Shelton, and Chuck Winkle. "Differential susceptibility of tree species to oviposition by periodical cicadas." Ecological Entomology 34.2 (2009): 277-286.
Yang, Louie H. "Periodical cicadas use light for oviposition site selection." Proceedings of the Royal Society B: Biological Sciences 273.1604 (2006): 2993-3000.