The incessant chirping in the blistering midday heat is unbearable and almost painful. And yet the insects that produce the deafening high-pitched notes are rarely spotted. Many people know the sound but have never seen a cicada. Although, according to Prof. Martin Villet of Rhodes University in South Africa, in Namibia alone there are 48 species of cicadas divided into 19 genera. Some species have not even been described properly and their existence has been established only through a single specimen. In general, virtually nothing is known about these insects.
There are about 140 species in southern Africa. Many are endemic, including four or five of the species found in Namibia, says Prof. Villet. Most of the local species have no common name and are only known by their Latin names. Munza laticlavia, which is also found in Windhoek, occurs in the Kalahari region of Namibia, Botswana and South Africa, especially on camel thorn trees (Acacia erioloba) and candle thorns (Acacia hebeclada). According to Namibian scientist John Irish, at least one cicada species lives on grasses in the Namib Desert. Most cicadas are found on trees and shrubs, where they feed on plant juices during the short time of their adult life.
Only the males “sing”. A chirping male is often surrounded by other males which keep quiet, however, and immediately sidle up to a female lured by the chirping. John Irish explains that male cicadas are able to close their ears to their own loud chirping. Cicadas can produce sounds measuring up to 120 decibels, which is close to the level of jet planes. For us humans, volumes around 50 dB (normal conversation, croaking frogs) are pleasant, discomfort sets in at about 100 dB (circular saw) and at 120 dB the pain threshold is reached. Most cicadas chirp away while sitting well-camouflaged on branches and twigs, but some species are “singing” in flight to attract females. At least one species in Namibia produces a volume of 106 decibel.
Noises in the 0.5 to 25 kilohertz range are generated with the tymbals. Only cicadas which belong to the group of cicadomorpha can produce sounds that are audible for humans. They use a pair of tymbals, a special structure below each side of the anterior abdomen. The tymbals are buckled and unbuckled by muscular action. They are often concealed by a lid, which starts at the last breast segment, and by a plate right on top of them. A large air sac directly below the “singing muscle” provides the necessary resonance.
Females cut slits into the bark of branches to deposit their eggs. After hatching, the nymphs climb from the tree or bush and burrow into the ground with their powerful front legs. Sometimes they live subterraneous for a very long time, feeding on root juices. All of them remain underground for at least a year, some of them up to a decade, before they return to the surface. At that stage the nymphs have a length of one to two centimetres. They scramble up a tree trunk and shortly afterwards moult into the adult insect, which is immediately able to fly. Only the dry and hard exoskeleton is left behind on the tree. The life of a fully grown cicada lasts less than four weeks, during which time it has to find a partner, mate and reproduce. To make matters more difficult, cicadas have numerous enemies, including many species of birds such as bee-eaters.
Virtually nothing is known about the life cycle of Namibia’s cicadas. Some species specialize in specific plants, but much more research is needed to understand these small insects. Most of them are about 2.5 cm long with a wing span of 6 to 8 cm. We are familiar with their formidable ambient noise, but almost everything else about them is still a mystery.
Author: Dirk Heinrich