But curiously it is not, as you might expect, their children that come back next year, its their siblings and cousins.
If you are a cicada you have a loooong, loooong childhood and a tiny adulthood.
Australian cicadas spend 6-7 years hiding in the soil in their youth, before climbing up a tree to emerge, leaving their carapace behind. - then into their all singing, reproducing and quickly dying maturity.
Cicadas have piercing mouthparts which allow them to be the most ineffectual vampire eat-alike of them all. For cicadas drink plant sap. Now that seems pretty sensible, lots of insects feed off of phloemey goodness - phloem is the plant transport system that carries energy rich sugars around their possibly massive bodies. Aphids drink it and can reproduce phenomenally fast - a full generation from birth to having their own babies can be as little as 5 days (ooh aphids - now there is a fun fact for another day!).
So why do cicadas grow so slowly - with all that sugary goodness ready to give them a boost?
Well THEY DON'T DRINK PHLOEM. Now don't ask me why, but for some reason they drink from the Xylem vessels instead. Xylem is the plant's other transport system. The one that transports water and a few salts up from the roots. It does contain a few amino acids, but energy rich it is not.
If Phloem is hot chocolate, then Xylem is a weak camomile tea.
But Why? I told you not to ask why! I don't know. I imagine just to mess with the entomologists studying them. But if you find out let me know!
Erm not quite. There is an allusion to a pun in the title that I haven't completed yet.
So lets talk super slow growing mathemagical NORTH AMERICAN CICADAS!!!!
In the US, its not every summer you hear their song, just every now and then, and ever time you do hear them its DEAFENING.
There are two awesome features about these dudes, and the first is that they are synchronous. In each location, they all moult into adults in same summer as each other. So every few years ALL the cicadas in one location emerge from their xylem drinking homes at once to sing their songs and die.
BILLIONS OF THEM
MILLIONS PER HECTARE
ALL AT ONCE.
So for a few summers its just quiet gentle summery stuff, then one year its CICADA NOISE MAYHEM.
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- If a few of you hatch each year, then a few of you will get eaten by predators, and that additional nutrition will help the predator numbers grow, so the next year there will be more predators around to eat you. The predator numbers won't keep going up, the cicadas and then predator numbers are likely to crash, and a cycle will form (more on that later), but overall cicadas hatching every year can lead to a higher predator number in the area and so fewer cicadas. But if the cicadas only emerge to be eaten every 10+ years, then a predator population cannot maintain its high numbers between feasts, so each emergence will be fed on less.
Fuuew, did that make sense? I hope so. Cause it gets cooler...
Not only are the cicada emergences synchronous they happen a very specific number of years apart
A PRIME NUMBER OF YEARS APART.
- Some species emerge every 13 years.
- Some species emerge every 17 years.
None emerge every 12 or 16 years.
WOW - MATHemaAWESOME!!!!!
- Prime number joy!!!
So again you ask: Why?
Remember those predator-prey cycles? (the ones I emphasized with colour, italics and underlining)
Now a 12 year emerging cicada species is could meet a predator boom for any predator whose cycle is every 1, 2, 3, 4, 6, or 12 years - all of these numbers divide into twelve.
But a 13 year emergence cycle and its "YES!" - meeting possible predator booms are much less common. A 3 year predator cycle will meet it every 3 x 13 = every 39 years instead of every 12! 17 works in much the same way. So North American Cicadas are protected by maths! - Wow, that's PRIM(E)al!!!