niuc wrote:...cicada in my hometown, quite "fat" and kept "singing"...
[ APOLOGIES FOR TURNING THIS INTO A BIOLOGY FORUM

]
Hi Niuc,
Yes, one of the distinctive feature of the cicada is its "fatness". Crickets are "slim" and "agile", and will hop away quickly if you try to catch them. Cicadas are very "calm" and "docile", and you can play with them in your hand - they'll just sit there, staring with their bug-eyes (and, as you say, "singing")!
Cicadas have a very unusual background actually. Apparently they live as larvae/grubs in the ground for 7-17 *YEARS*, and then emerge suddenly in huge groups, turning into the familiar "cicada". I don't remember how long they survive once they come out of the ground, but it's only on the scale of days or weeks, very much less than the years which they have spent in the ground.
The interesting thing is that each species of cicada has a different cycle. That is to say, species X emerges once every 11 years, species Y emerges once every 13 years, and species Z emerges once every 17 years, etc. When they emerge, the *whole group* (for that species) emerges, they breed, lay eggs, and the eggs hatch out, and they burrow into the ground and we don't see that species for the next 11, 13, 17, etc years.
One of the mysteries is that, apparently, the length of the cycle is almost always a prime number (a number which can't be divided by other numbers). The standard explanation for this is that this is nature's way of making sure that different species don't overlap in the time they come out of the ground. If the numbers were *not* prime, e.g. species X every 4 years, and species Y every 6 years, then once they came out in the same year, then they would keep overlapping every 12 years (the lowest common multiple of 4 and 6). They would then compete for food every 3rd time that X emerges and every 2nd time that Y emerges. When the period of emergence is a prime number, then the lowest common multiple of two prime numbers is very much larger (you have to multiple both numbers together), miminizing the number of times they overlap.
Here are some pictures from the net, some of cicadas themselves, and some of the empty shells they leave behind on tree trunks and on the ground, when they hatch out.
Cicadas:
http://www.1000plus.com/Charleston%204t ... a_6286.jpg
http://www.cirrusimage.com/homoptera/cicada_2.jpg
http://www.chefscott.com/recipes/cicada14.jpg
http://www.carinemily.com/cicada/images ... lt-014.jpg
Shells:
http://www.zentropolis.com/2004_cicadas ... 20Tree.jpg
http://www.thepotters.info/archives/cicada.jpg
http://nfg.2y.net/grafx/family/Cicada_Shell.jpg
Only the first 2 pictures of cicadas look like the ones I know from Malaysia. The others are also very clearly cicadas (they have that "fat" look), but still look quite different from the Malaysian ones.
Sim