Magic species: 17-year cicadas in northeast U.S.

17 years. Time enough for a newborn to grow up as an adult. The number also marks the length of life of the longest-living insect in North America.

This year, the wait is finally over for some of them. With the 2016 summer coming, another batch of 17-year cicadas have finally come out of the ground and hatch in parts of several Northeastern states.

Apart from the 17-year cicadas, there are also 13-year ones. They belong to the genus Magicicada, which is an eastern United States genus. In some parts of United States, it makes a grand scene when these insects come out, usually in huge numbers, after such a long time, when piles of cicada skins can be found on the ground.

MISUNDERSTANDING OF LIFE OF CICADAS

Even for common summer cicadas, it is not like some of us assumed they only live for one month. When summer comes to an end, they die. The life of most summer cicadas is around three to five years, but there is an annual emergence.

"Most of their lives are spent as immature nymph stage in the ground," explained Louis Sorkin, an entomologist at American Museum of Natural History.

"And when it is time, the temperature plays a part in getting that nymph to realise that it has to come out now."

Most of this year's bugs are known as Brood V of Magicicadas. Starting May, the insects are seen popping out of the soil in New York, Maryland, Ohio, Pennsylvania, Virginia and West Virginia. At this moment, their life is coming to a closure.

Periodical cicadas emerge periodically, but that doesn't mean the whole family would wait to come out altogether. Different broods come out at different time, and in different places. According to Professor Sorkin, this is a good way for them to avoid predators.

"If there are any predators feeding on any of these cicadas, it doesn't really reduce that population that much because there's so many cicadas and so many predators," said the professor.

According to him, the nymphs hatched from the eggs in about 10 weeks. In their lengthy 17 years down under, the nymphs are attached to the roots of the plants suck fluids from there so as to grow.

PRIME NUMBERS

Why they all choose 13 or 17 years as their time of a life cycle has also triggered a lot of curiosity in entomology studies.

"13 and 17 are prime numbers," said Professor Sorkin, "and it seems that these prime numbers were the best, through revolution, these came out to be the best to not have any predators that can live long enough to actually able to follow them."

"Being an odd number is good too but having that minimum prime number that work really well because it is a very long time period from one to another. There's no predator synchronised along with that too." he added.

This is just a speculation at this moment, though. Why exactly the evolution chooses this two number is still a mystery. And research is still going on to dig out more about this magic genus. Endit