People ask: why do periodical cicadas stay underground for 17 or 13 years? <\/p>\n
There are three parts to this puzzle that people are interested in:<\/p>\n
Cicadas likely don’t count like people do (“1,2,3,4…”) and you won’t find scratch marks inside the cell (where they live underground) of a Magicicada, marking off the years as they go by. However, there is a kind of counting going on, and a good paper to read on that topic is How 17-year cicadas keep track of time<\/strong> by Richard Karban, Carrie A. Black, and Steven A. Weinbaum. (Ecology Letters<\/em>, (2000) Q : 253-256). By altering the seasonal cycles of trees they were able to make Magicicada emerge early, proving that cicadas “count” seasonal cycles<\/strong>, perhaps by monitoring the flow and quality of xylem sap, and not the passage of real time. <\/p>\n Why prime numbers<\/strong>, and why is the life cycle<\/strong> so long? This topic fascinates people. The general consensus is that the long, prime-numbered life-cycle makes it difficult for an above-ground animal predator to evolve to specifically predate them. Read<\/a> Emergence of Prime Numbers as the Result of Evolutionary Strategy<\/strong> by Paulo R. A. Campos, Viviane M. de Oliveira, Ronaldo Giro, and Douglas S. Galvao (PhysRevLett<\/em>.93.098107) for more on this topic. An argument against that theory is that a fungus, Massospora cicadina, has evolved to attack periodical cicadas regardless of their life cycle. Of course, a fungus is not an animal. Maths are easy for fungi.<\/p>\n