letting nature back in

So loud and so tantalizingly near, cicadas tend to fall silent when approached, and their camouflage colours make them hard to see. But recently I was in luck as after hearing a faint cicada-like squeak from a tree, I stood still and scanned the stems of the tree methodically and then suddenly several cicadas became surprisingly obvious.

It was late on an overcast afternoon when walking in our garden and passing the horsewood/perdepis tree (Clausena anisate) that I heard a brief squeaking from a cicada somewhere in the tree at about head height. It took quite some time in the dim light for my eyes to distinguish first one cicada and then after a minute or two I counted a total of nine cicadas, all perfectly still and silent relying on their cryptic colouration to conceal them.

In the low light their mottled appearance seemed to mimic lichen on the branches of a tree. As it was too dark that afternoon for successful photography, the next morning I went out when it was light enough to see if the cicadas were still there – and they were. These photos were taken the next morning when the light was a bit better, ahead of gathering clouds on another rainy day.

These cicadas are quite large – about 5 cm (2 inches) in length. According to Jason Londt in his book Suburban Wildlife in KZN, the commonest suburban cicada is the giant forest cicada (Pycna semiclara), but I cannot be certain of the ID of the cicadas I photographed. There are about 140 cicada species in South Africa, with about 38 species known to be in KwaZulu-Natal, with 16 of these species being endemic, many limited to quite specific areas (Armstrong & Villet, 2019).

Looking at several photographs online and in books of the giant forest cicada, they appear greener in colouration than the ones I saw, and their eyes are brown rather than green.

Perhaps these green-eyed cicadas are giant forest cicadas, perhaps not, but in common with all cicadas, it is the males that call. They do not stridulate (like crickets for example) but have two tymbals (round sound-producing organs on either side of the abdomen). These tymbals appear to be two round membranes each reinforced by a strong ring. Using muscles to contract this membrane and allow it to recoil is how the cicada produces its sound. The sound is amplified by an air chamber below the membrane and multiple layers over the membrane can be manipulated to modify the pitch of the call.

The call serves to attract potential mates and the giant forest cicada also has a more trilling territorial call. For giant forest cicadas (and the species in our garden) once one male starts his very high, loud and continuous call other males join in a chorus that is so piercing it is difficult to locate with any precision where the sounds are coming from.

For a brief moment one of the cicadas started calling while I was watching. I was not sure which one was calling, but then I noticed a visible vibration on one of them, at the point where the wings start to meet in the middle of the back – about where the two black dots/stripes are visible where the wings almost meet as seen in the photo above.

The life-cycle of cicadas is most interesting and in their larval stages, which take place underground, some species of cicadas live for many years. For more about these interesting bugs see my post that was inspired by the terracotta exoskeletons of cicadas that I found in the garden.

The little red dots that resemble jewel-like droplets visible on the ‘forehead’ of the cicada are in fact ocelli, three primitive eyes that are sensitive to light and are used in conjunction with the large compound eyes.

In conclusion, perhaps I should explain that this week several neighbouring suburbs, including ours, had no electricity for four days (due to damaged underground power cables). This longish outage stretched the capability of our small home backup system as well as affecting the reliability of connectivity to the Internet. It was a huge relief when power was restored last evening.

Consequently, I was delayed in preparing and publishing this post. Also, I am even more behind than usual in my reading of the many blogs that I enjoy – so I apologise for that and hope to do some catching up in the week ahead.

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Sources:

Armstrong, Adrian John; & Martin H Villet. 2019. Checklist, endemism, English vernacular names and identification of the cicadas (Insecta, Hemiptera, Cicadidae) of KwaZulu-Natal, South Africa. African Invertebrates 60(2): 165-193. https://africaninvertebrates.pensoft.net/article/35130/; Londt, Jason. 2009. Suburban Wildlife in KZN. A Wildlife Handbook, WESSA KZN; Picker, Mike; Charles Griffiths & Alan Weaving. 2019. Field Guide to Insects of South Africa. Cape Town: Struik Nature.

Posted by Carol