letting nature back in

Cicadas are best known by the loud high-pitched sound adult male cicadas make mostly during the months of summer. Even though they are loud they are hard to locate and so well camouflaged they are difficult to spot, and typically we only see cicadas that have accidentally bumbled indoors. But sometimes we may come across exoskeletons left behind by cicada nymphs at the time of their last moult into their winged adult form.

Cicada nymphs live a subterranean life adapted to digging and feeding on the sap of roots. Most of a cicada’s life is spent in this larval state underground where they can be as deep down as 2.5 metres. For most species life underground is for two to five years, but there are some North American species that can live underground for as long as 17 years.

Exoskeletons of cicada nymphs can remain clinging to the bark of trees for a long time after the adults emerge from this final moult

Cicada nymphs have strong front legs adapted for digging and a single mouthpart for sucking plant fluids. Adults too have a single beak-like mouthpart for sucking fluids from plants. Cicada nymphs go through about five moults or instars during their lives underground. For the final moult when they become adults they emerge from the ground and climb up the trunk of a tree beneath which they have been living and there they shed the exoskeleton in their final moult. In some species the nymphs emerge in groups known as broods.

In late April this year I found many shed cicada nymph exoskeletons on the same tree and on some adjacent trees. It appears that the nymphs emerged as a group. As they are small and well camouflaged they are tricky to photograph

The empty exoskeleton is easier to see on a tree with paler and less fissured bark. I found at least 20 exoskeletons that remained on the tree trunks or that had fallen to the ground

There are over 3000 species of cicada in the world distributed over all continents except Antarctica, with about 150 species occurring in South Africa. Most species are fairly restricted in their range. Although in South Africa they are often referred to as Christmas Beetles (because their singing is associated with the summer Christmas holidays), Cicadas are bugs and not beetles.

Bugs have needle-like or beak-like mouthparts for piercing and sucking, whereas beetles have chewing mouthparts. Their wing structures are also different. Most bugs have membranous wings with only the base of the forewing being thickened. In most beetles the forewings, termed the elytra, are thickened and hardened so as to form an apparent casing that covers the hind wings when folded. To fly the hardened forewings are lifted to reveal the thin and membranous hindwings used for flying. Think for example of a ladybird (incorrectly sometimes called a ladybug although it is in fact a beetle). There are also differences in the composition of the antennae, with bug antennae comprising 4 or 5 segments whereas the antennae of beetles have about 11 segments. Bugs have an incomplete metamorphosis cycle with the nymphs resembling the adults and they do not pupate, whereas most beetles are grub-like in their larval stage and pupate before they become adults.

If you look carefully you can see the cicada that I photographed at Cape Vidal on the north-eastern coast of KwaZulu-Natal. As it is so well camouflaged I only saw the cicada after it emitted a low buzzing sound as I walked by. It was perched on the trunk of a tree at about head-height and so I was able to spot it

It is easier to see in profile

This large adult cicada was perched in vegetation on the banks of the Pongola River in Ithala Game Reserve in KwaZulu-Natal. I came across it by chance while I was watching a butterfly

In our garden I collected some of the cicada nymph exoskeletons that I found had fallen to the ground. The strong digging forelegs are clearly visible. Grouped together and placed on white paper they resemble a small terracotta army

Sources:

Cicada Mania. 2019. https://www.cicadamania.com/; Lakna. 2019. What is the difference between a bug and a beetle. https://pediaa.com/what-is-the-difference-between-a-bug-and-a-beetle/; Wikipedia. 2019.  Cicada. https://en.wikipedia.org/wiki/Cicada

 Posted by Carol