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aren’t able to initiate new broods. 8. Why such a long "hibernation?” A. Nearly all insects are heavily preyed upon by birds, reptiles, other insects, etc. Each insect species has evolved its own protection mechanisms. (For example, the honey bee's main protective mechanisms are its social behavior and stinging capability. The cicada’s mechanism for protection of the viability of its species is best described as “predator satiation.” By remaining out of sight for long periods and simultaneously appearing in huge numbers, predatorpressure can’t possibly wipe out a population.
In order for this protective mechanism to be effective, the life-cycle period must be longer than the life span of potential predators.
9. Why is this life cycle 17 years exactly? Wouldn’t 15, 16 or 18 be just as efeective?
A. No. A 17-year life-cycle has two advantages—it’s along enough period to exceed the life span of a potential predator, and it’s a prime number (that is, the number 17 is not evenly divisible by any other whole number). Therefore, a potential predator’s life cycle is unlikely to coincide with a cicada “hatch.”
In order for this coincidence to ever occur for 2 or more successive “hatches" (which would quickly knock back the cicada population), a potential predator would have to evolve a life-cycle of precisely 17 years.
Does this prime-number explanation seem farfetched? If so, consider that the periodical cicada, in the southern part of its range, emerges every 13 years! (13 is also a prime number.)
10. How do the nymphs count the 17 years and all emerge at once?
A. No one knows.
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