One of the first signs of the change in season for me can be seen in the smaller sounds and creatures that begin to appear. The occasional fluttering of a butterfly across the road, to the life that comes alive from open grassland areas as you drive past – you can’t help but feel the arrival of summer.
One insect in particular (heard much more than it is seen) is the harmonies from the buzzing cicadas. Cicadas are true insects and around 140 species of 1300 species occur in South Africa. These insects occur on every continent except for Antarctica as they thrive in warmer climates.
The first time I came across a cicada beetle was on the banks of the Kowie River in Port Alfred, Eastern Cape. My dad had called me outside, ‘just come look here’ which I reluctantly did. There on the trunk of a tree was the exoskeleton of a cicada. A perfect replica of what once lived inside. I found this fascinating as I had no idea this creature existed let alone its ability to shed its exoskeleton. Years after that I would acknowledge the presence of the insects when hearing their familiar call but never really dove too deep into their existence.
The most fascinating thing about these insects I found was their unexpected life cycle. The cicadas that we hear and occasionally see are at the very end of their life cycle. These insects spend most of their lives underground as a nymph before transitioning into their final stage and emerging as adults. The truth is that the biology of these insects is poorly understood, depending on the type of cicada beetle- it can take from 2 to 17 years to reach adulthood thus spending most of those years underground.
While above the ground they are mostly found in trees as they feed on the tree sap. They are able to do this with their specialized mouthparts known as proboscis which allows them to suck the tree sap. They cause no harm to the host tree, but rather actually assist it in eating excess sap, feeding on leaves, and due to their size act as a form of pruning as well as deposit a natural fertilizer at the base on the tree which returns nutrients to the ground.
To other animals such as birds, mammals, reptiles, and even fungi they are an incredibly important food source, especially for birds as they are high in protein content and thus with them reappearing in summer, support the returning migrating bird species and abundance of life which comes with the summer rain. These little insects really do fulfill an important niche in the entire ecosystem.
Cicadas are typically heard through their constant buzz which is created by tymbal organs, in a nutshell, they are sound-producing membranes that are round in shape and located on either side of their abdomen. Although much smaller than the lid of a ketchup bottle, as you press it in it clicks in and out, it is a great example of how the tymbal organ of the cicada works. A muscle is attached to the centre part of the circular membrane which contracts and relaxes rapidly producing the high-pitched clicking sound. Interestingly, due to the sound produced both male and female cicadas have ears so that they are able to hear the mating buzz of the male cicadas.
The start of a single male’s call not only begins the laws of attraction but also stimulates other males to begin their call and therefore a familiar buzz of summer is created in a chorus. The use of a suitable tree also allows the sound to bounce back off the bark resonating as a louder sound that will travel further. The high-pitched buzz is something rather remarkable as it can reach up to 120 decibels which is the same frequency as that of a jet engine – an impressive sound to be produced by a small insect. So, in essence, the loud buzz of summer is the mating chorus of the cicadas. After a male and female unite through compatible calls they are attracted to, they will mate and the female will fall pregnant.
A sad reality is that once they have mated, the male dies while the female finds a suitable laying place. She will then fly to a suitable tree and use her ovipositor (egg-laying organ) to create a small fissure in the bark of the tree where she will deposit her eggs. Once she has laid the fertilized eggs she too dies soon after – thus the cicada life cycle begins again. The eggs hatch from the slit in the tree and drop to the ground where they then burrow themselves underground and begin to excavate tunnels towards various root systems, creating a network of burrows as they manoeuvre themselves to find sap from tree roots to feed on.
Over the many years, they continue to evolve until reaching their final stage, where they tunnel back up to the surface and climb up the tree before morphing into adulthood. They do this by shedding their exoskeleton and leaving it on the tree bark as they begin to embark on their breeding season and final stage of life. All those years ago I had just seen a fraction of a cicadas life cycle.
I find it quite fascinating that only in summer do we really notice these little insects yet years even decades they have lived beneath the very ground we walk on foraging and surviving only to make their way to the surface for a brief period of time. For me, the chorus of cicadas is one of those sounds that I strongly associate with the bush – it’s a sign of life that can be heard and not always seen. It’s the buzz of summer that you can hear and feel produced by a little insect that has lived long before.
Maybe the next time you are here and hear the summer buzz, see if you can find one of these incredible insects.