Cicadas

The classic insect life cycle seems utterly bizarre to beings whose physical existence takes place in only one form and one body. The cicada's story is even more peculiar than most other insects, for this little fellow spends by far the greater part of his life underground, only reaching adulthood and gaining the freedom of the skies in the last few minutes of the eleventh hour.

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Some species of cicada spend up to 17 years grovelling in the dirt, sucking the sap of roots and tubers, before they finally emerge and take their adult form.
The cicadas in this photo library are all members of the Mediterranean species, Cicada orni, and they spend a mere 8 to 10 years as grubs. As the summer of their adulthood approaches each cicada larva digs a tunnel towards the surface, but the first ones do not break out of their tunnels and emerge into the air until the temperature outside is around 30 degrees centigrade.

The cicada always emerges beside the stem of a bush or plant, and having emerged it climbs up the stem, generally to a height of about 18 inches. Here, it splits its a skin. The repeated shedding of the skin as the larva grows is a feature of other insect life cycles (for example, the grasshoppers and the mantids) and the cicada grub will already have shed its skin several times while it was in the soil. On this occasion, however, it emerges from its old skin equipped with a pair of huge, transparent wings.

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The adult cicada still drinks sap, but its real purpose in life now is to meet other cicadas and mate. To enable it to find other cicadas each creature is equipped with an apparatus - the "timbals" - which it vibrates at immense speed, thereby producing an extraordinary zinging, churring noise. The noise is so loud that it can be heard from at least 100 yards away and so strident and intense that a human observer standing near to the bush where the cicada lurks will find himself quite disorientated. Sometimes it almost sounds as if the insect has managed to get inside your head!

Most of these cicadas were photographed on Isla Perdiguera (Murcia, Spain). It seems to us that the behaviour of the cicadas here is distinctly different from that of their mainland counterpart, and we also believe that that they make a slightly different noise. Presumably they do not get much chance to mingle with the larger population of Spanish cicadas. Thus, like Darwin's finches, they are very gradually evolving new habits.


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