Cicadas- Boys and their noise
Boys and their noise
Been serenaded by a chorus of cicadas lately? Don’t begrudge them-it’s
Louder than most insects, cicadas flood forests and orchards with their ear-splitting “concerts”. While many people have experienced the din that cicadas create, few have actually seen the insects responsible. In most species-about 150 recorded in Thailand-their colourations make them hard to spot on the bark of trees where they like to hang out.
Over the past several weeks, cicada calls were heard in many places, including some areas in the Bangkok suburbs. Perhaps it’s a good idea to learn something about them.
Apart from the occasional bursts of their deafening choruses, another obvious cue to cicada presence is the brownish “skin” the nymphs leave behind on tree trunks-this skin is shed during their final moult on the way to becoming adults.
Only during this mature stage can they make their unmistakable calls.
Actually, the noisy adults are all males. And their “songs” are not made by singing-insects can’t sing-nor by rubbing their wings like crickets. Instead, the sound comes from vibrations in a pair of specialised organs on the abdomen called “tymbals”.
Females do not have these organs.
At this time of year, male cicadas usually gather in large numbers on trees and shrubs. They play their songs in unison to attract mates.
To human ears, these songs may all sound similar. But the truth is that different species play different songs-each of which is rendered in a specific frequency and timing to make sure the girls end up with the right guys, those of their own species.
Like many insects, reproduction is the priority of adult cicadas, and they have just a few weeks to accomplish this mission. Males die soon after mating, females after they have laid their eggs.
The common Meimuna opalifera, for example, produces about 200 eggs in each clutch. After around 120 days, tiny hatchlings break out from the eggs, which are deposited on trees, and drop themselves onto the ground.
Armed with a pair of digging legs-the front pair-they burrow into the soil where they spend much of their lives, feeding by sucking nutritious sap from plant roots.
Underground, the nymphs moult three to four times each month and every time they grow bigger. They spend several years in the dark subterranean world-from five to 17 years, depending on species-and never reappear above ground until it’s time to crawl up tree trunks for the final metamorphosis.
During this crucial process-which normally occurs in the dry season, particularly in March and April-a new adult slowly slips out of its brown nymphal skin through the slit in the back. It takes about half an hour before the insect completely frees itself from the old skin.
The newly-emerged cicada appears pale green, but after a while the colour darkens and the initially soft body hardens. Most of the more common species have brownish colourations, while some forest species are brightly coloured.
The new adult’s wings first come out folded but they gradually spread out as blood is pumped into the veins. The digging front legs have disappeared, replaced by a new pair which look like the others.
This transformation process usually takes place during night-time when there are fewer predators around. Still a lot of emerging nymphs fall prey to frogs and toads before they reach a safe spot on the tree trunk.
Even after a new adult finally breaks out of his nymphal skin, it takes some time before the insect becomes strong enough to fly and fend for itself. During his vulnerable moments, the helpless cicada is an easy target for owls and other predators, including humans. Villagers in the North and the Northeast consider the insects a delicacy.
Well, it seems cicadas do much more than just make loud noises. Despite their brief existence in sunlight, they manage to do good to the ecosystem, as well as to some people’s lives.
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