Insects
Cicadas
After a few relatively quiet years we have just had a bumper summer for cicadas. No-one seems to know why they choose particular years to come out in such numbers. In fact there is much about these creatures still to be discovered.
Cicadas exist all over the temperate and tropical world with over 1000 species recorded. Australia has the most and the greatest variety of species with several hundred known species. Well over 20 of them are found on the Central Coast.
They are the loudest of all insects, exceeding 120 decibels at close range, close to the pain threshold of the human ear. On the other hand, the call of some species is so quiet that they can barely be heard at all.
They have great names, probably bestowed by children. Some describe their appearance such as Greengrocer, Yellow Monday, Red eye, Black prince and Floury baker. Others describe their call: Sandgrinders, Red roarers, Green whizzers and the Southern squeaker.
Cicadas exist all over the temperate and tropical world with over 1000 species recorded. Australia has the most and the greatest variety of species with several hundred known species. Well over 20 of them are found on the Central Coast.
They are the loudest of all insects, exceeding 120 decibels at close range, close to the pain threshold of the human ear. On the other hand, the call of some species is so quiet that they can barely be heard at all.
They have great names, probably bestowed by children. Some describe their appearance such as Greengrocer, Yellow Monday, Red eye, Black prince and Floury baker. Others describe their call: Sandgrinders, Red roarers, Green whizzers and the Southern squeaker.
Life cycle
Cicadas have three distinct life stages — egg, nymph and adult.
Females lay two or three hundred 3mm eggs in their favoured tree, The relationship between the different species and the vegetation they prefer to live in and on is still poorly understood. The eggs take up to four months to hatch as nymphs.
The tiny, spindly nymphs leap to the ground and burrow in, digging a tunnel to a tree root, where it latches on to feed on sap. They feed through a specialised proboscis called a rostrum. This is a thick, needle-like protrusion that penetrates the root’s flesh and sucks up nutrients from the xylem.
Cicada nymphs are quite active under the ground where they stay for years at a time. How many years is still a matter for debate - estimates range from 3 to 10 years. It probably varies between species and is affected by the climate.
When the time is right, sometime after rain between September and November, they dig themselves out and climb up a nearby tree. At this stage they have a hard shell. The nymph attaches itself firmly to the bark and then a lengthways split appears in down the back of the shell. Over a couple of hours the adult cicada emerges and unfurls its wings by pumping fluid into them. The empty shells are commonly found dried out and attached to vegetation.
After a short time for rest and recuperation, the adults spend a few weeks dedicated to eating their fill, calling like mad and hopefully having sex.
The adults, like the nymphs, have a straw like protuberance to suck sap from the tree, and if alarmed have been known to fly off, leaving it embedded in the tree’s flesh.
Cicadas have three distinct life stages — egg, nymph and adult.
Females lay two or three hundred 3mm eggs in their favoured tree, The relationship between the different species and the vegetation they prefer to live in and on is still poorly understood. The eggs take up to four months to hatch as nymphs.
The tiny, spindly nymphs leap to the ground and burrow in, digging a tunnel to a tree root, where it latches on to feed on sap. They feed through a specialised proboscis called a rostrum. This is a thick, needle-like protrusion that penetrates the root’s flesh and sucks up nutrients from the xylem.
Cicada nymphs are quite active under the ground where they stay for years at a time. How many years is still a matter for debate - estimates range from 3 to 10 years. It probably varies between species and is affected by the climate.
When the time is right, sometime after rain between September and November, they dig themselves out and climb up a nearby tree. At this stage they have a hard shell. The nymph attaches itself firmly to the bark and then a lengthways split appears in down the back of the shell. Over a couple of hours the adult cicada emerges and unfurls its wings by pumping fluid into them. The empty shells are commonly found dried out and attached to vegetation.
After a short time for rest and recuperation, the adults spend a few weeks dedicated to eating their fill, calling like mad and hopefully having sex.
The adults, like the nymphs, have a straw like protuberance to suck sap from the tree, and if alarmed have been known to fly off, leaving it embedded in the tree’s flesh.
How Cicadas Sing
The males of each species has it’s own distinctive call which is performed to attract a mate.
The males tend to group together when calling which increases the total volume of noise and makes it hard for birds to locate them. Some species call in waves with just a few individuals at first then more and more joining in until a deafening crescendo is reached, which drops as more individuals stop calling. This behaviour might also reduce the chance of being eaten.
The sound is produced by organs called tymbals, which are situated on each side of the base of the abdomen. Each tymbal consists of a ribbed membrane that has an internal muscle attached to its centre. The membrane buckles inward when the muscle contracts and snaps back to its neutral position when the muscle relaxes. Sound is produced by both movements in much the same way as pushing an empty can in and out
Rapid contraction and relaxation of the muscle can produce sounds at such high frequency that we hear a continuous note.
Different species have developed different ways of modifying and amplifying the note produced. Air chambers in the abdomen, flexing the abdomen into different positions, clapping their wings while calling and variations in tymbal structure all vary the sound produced.
The males of each species has it’s own distinctive call which is performed to attract a mate.
The males tend to group together when calling which increases the total volume of noise and makes it hard for birds to locate them. Some species call in waves with just a few individuals at first then more and more joining in until a deafening crescendo is reached, which drops as more individuals stop calling. This behaviour might also reduce the chance of being eaten.
The sound is produced by organs called tymbals, which are situated on each side of the base of the abdomen. Each tymbal consists of a ribbed membrane that has an internal muscle attached to its centre. The membrane buckles inward when the muscle contracts and snaps back to its neutral position when the muscle relaxes. Sound is produced by both movements in much the same way as pushing an empty can in and out
Rapid contraction and relaxation of the muscle can produce sounds at such high frequency that we hear a continuous note.
Different species have developed different ways of modifying and amplifying the note produced. Air chambers in the abdomen, flexing the abdomen into different positions, clapping their wings while calling and variations in tymbal structure all vary the sound produced.
