If creepy-crawlies give you the creeps you might consider skipping today’s blog. Not for the faint of heart. But, oh, so fascinating in terms of what nature has, once again, to offer, and in terms of the utter cluelessness of science in answering some very big questions. Skip right to the end to listen to Bartok’s piano piece which will enrich your day.

2021 is the year where the central and eastern U.S. is expecting a mass emergence of cicadas, millions and millions of them who leave their burrows underground and climb the trees in synchronized fashion, for a 6 week-short life- span of reproduction after having been underground for 17 years.

They are known as periodical cicadas. Only 7 of the 300 species of cicadas worldwide have this strange life rhythm, waiting for 17 or 13 years, respectively, to then come up all at once. While developing underground they suck the liquid of plant roots, apparently counting the seasonal pulsed of fluid flowing from those roots – when the plants have completed 13 or 17 cycles and the temperature has gotten warm enough (65º/18º) they know to emerge. During the long time underground they molt their shells 5 times – and not all at the same speed. But somehow towards the end of that interval the more developed nymphs wait and the lagging ones catch up, so the they are all ready for time x, ready to fly and populate the trees where they mate and lay eggs. No one knows how they pull that off.

Unlike locusts that devour crops, cicadas are good for our ecosystem. Their weight en masse in the trees helps to prune weak branches, they release tons of nutrients into the soil after death and they serve as an abundant food source for all kinds of predators, four-legged and winged varieties included. This despite the fact that the sheer number of bugs (as many as 1.5 million may crowd a single acre) has anyone of them at practically zero risk for being breakfast, lunch or dinner. Although interestingly – and here is one of the unanswered questions – bird populations that are normally predators of annual cicadas decline just at the point where the periodical cicadas emerge. In the years before and after these birds a back to their normal population density.

So why these prime numbers – 13, 17, – for the emergence? We do not know for sure. Some mathematicians have offered the following hypothesis:

Both 13 and 17 are prime numbers, meaning they’re divisible only by 1 and themselves. This means that emergences rarely overlap with predator population cycles that occur in shorter intervals. For example, if cicadas emerged every 10 years, they’d be susceptible to predators whose population boomed on a cycle of one, two, five or 10 years. If they came out every 12 years, they’d be a tasty snack for any predator on a cycle of one, two, three, four, six or 12 years. Thirteen years, though? Only one and 13. The same goes for a 17-year cycle.

Climate change might put and end to that, too. Scientist are seeing shorter emergence cycles on the horizon for cicadas, prompted by ever warmer temperature and speculated to come down to something like 9 years in the future – no longer a prime number. This implies far more exposure to predators, obviously.

Cicadas have one natural enemy that is not affected by time spans at all: a fungus named Massaspora which does an ugly job on them. Its spores colonize the backend of the bugs, disintegrating it while the cicadas are alive, while injecting the them with a compound similar to amphetamine that keeps them moving while dying. Thus they disseminate the spores across a larger area. For male cicadas it also has the weird effect that they start flicking their wings like females, attracting other males who then try to mate, getting immediately infected. Told you it would get creepy.

The short clip below is a marvel of time-lapse photography showing the life cycle of cicadas.

Photographs are of Maryland and Massachusetts birds, cardinals in particular, that will be in shorter supply this year.

And maybe not the best way to play: saxophone amidst the cicadas.

Here is a different musical take: “The most obsessive admirer of bugs was Bela Bartók. The Hungarian composer evoked the cicada in his 1926 piano suite Out of Doors, the fourth movement of which is called “The Night’s Music.” Here Bartók piles up tone clusters to create an eerie evocation of frogs, birds and cicadas that are audible right from the very beginning.”