The cicada – mostly heard, not often seen

While on safari during the hot and humid summer months here at Singita Lebombo and Sweni, you are more than likely to notice an extremely loud ear-piercing sound emanating from the lush vegetation growth, as you slowly meander along on your journey.

This sound comes from male cicada, the undisputed champion of loudness in the insect world, which produces the loudest sound that any insect can make. This high-pitched sound (or song), is actually the mating call of the specific cicada species. Each male of different species has its own unique sound which will only attract the female of the same species. These sound differences allow several different cicada species to coexist in the same area. Cicadas have been known to disappear for many years, reappearing in force once conditions are right – their abundance can be triggered by temperature, humidity and rainfall received at certain periods.

There are more than 3 000 described species of cicada globally, with about 150 known species in South Africa.

Cicadas are definitely more often heard than seen. It is amazing how incredibly difficult it can be to find an individual on the trunk of a tree, even while the loud pitched shrill is all around you. The reason for this is the fact that most species are cryptic, mimicking the colour of the tree bark on which they spend most of their adult life. This cryptic colouration assists in avoiding predation.

But how does the male cicada produce this sound? At the base of the abdomen, there is a specialised hollow plate known as a tymbal. The tymbal is convex in shape - this shape being important in how the loud shrill is made. By utilising a strong muscle, the tymbal is buckled inwards – similar to making a dent in the lid of a metal tin. By using the power of its own elasticity, the tymbal bounces back to its original position. It is then buckled inwards again through a further contraction of the same strong muscle, producing a clicking sound. The speed of this process is accelerated until the tymbal starts oscillating. The tymbal soon oscillates at hundreds of cycles per second, producing the high-pitched shrill sound.

Diagram showing the tymbal of a cicada

Male cicadas are the only insects capable of such a loud and unique sound. Large species can produce sound in excess of 120 decibels at close range. This is approaching the pain threshold of the human ear – a jet engine at take-off is 150 decibels which will rupture your ear drum so that gives you an indication of just how loud some species of cicada can be. Interestingly, smaller cicada species sing in such a high pitch, way above our hearing ability, that we cannot hear them at all. However, this has been known to cause domestic dogs and other animals to howl in pain as they have the ability to hear such high-pitched sounds.

Interestingly though, there are individuals of male cicadas species that do not make any sound at all. These are parasitic males and it is a common occurrence among cicadas. These males are mute and they do not expend any energy on singing. Instead, they search for a singing male or males and hide behind the branch or trunk on which the singing male or males are attached. It has been known for a single singing male to have three or four “thieves” waiting close by and out of site, trying to intercept any female or females that are being attracted by the singing males. This is actually a popular strategy and it succeeds more often than not. To see a video of a male cicada making the loud shrill sound, click HERE.

Another interesting part of the cicada is the very unusual life cycle or metamorphosis. Cicadas have a paurometabolic metamorphosis which is egg -> nymph -> adult. This is very similar to hemi-metabolic metamorphosis but differs in that the nymph and adult stages vary considerably. They also differ in terms of their place of living (habitat) and their activities (ecological niche) – this ensures that there is no competition for food between the adult and nymph. Nymphs spend their lives underground and can be periodic – most for two to five years, but some as long as 10 years or more – or annual (emerge every year). Once the nymphs are ready to change into the winged adults, they dig their way to the surface, emerging from the ground. They then climb about one metre up their host tree and shed their nymph exoskeleton. They then feed on the sap and xylem tissue of the tree and eventually fly off in search of a mate. Once mating has taken place, the adult female lays her eggs in a slit or crevasse of a branch of a tree and the cycle continues. Even though the adults can feed, this stage of their life cycle is not long at all, lasting no more than two months on average.

A. Underground nymph; B. Adult cicada hatching from the nymph stage; C. Hatched adult cicada; D. Cicada nymph exoskeleton.