Christmas confusion

WHAT comes to mind when you hear the word “Christmas beetle”? I was brought up in Johannesburg where Christmas beetles were actually beetles. When I came to KwaZulu-Natal I discovered that locals call cicadas­ Christmas beetles and that has always worried me because cicadas are not beetles, but bugs. Beetles belong to the insect order called the Coleoptera while bugs belong to a totally different order called the Hemiptera.

The Christmas beetles I was brought up on are those small (about one-centimetre long), shiny, brown beetles that come into our homes on warm nights around the time Christmas is observed by many people — hence the common name. So let’s talk about these beetles. They belong to the huge family called the Scarabaeidae, commonly called scarabs. There are literally hundreds of species divided into a number of subfamilies. Some, like the dung beetles and fruit chafers, are fairly well known because they are often large and are commonly seen feeding on animal dung or on fruit or the tender petals of our favourite flowers. These scarabs are also frequently brightly coloured and active during the day. Those that some of us call Christmas beetles are generally nocturnal and so we do not often encounter them feeding. They are fairly small and dull coloured and do not always catch our attention.

The life cycle of Christmas beetles is not complex. The adult female beetle lays its eggs in soil. When the eggs hatch the larvae burrow into the soil where they feed on decomposing plant material and in so doing recycle nutrients. Gardeners often encounter these larvae which have a fairly characteristic C-shape. When a larva has completed its growth it constructs a chamber out of soil in which to pupate. The adult beetle emerges from the pupa, makes its way to the soil surface and flies off to feed and reproduce. The adults feed on a wide range of plant matter and may, depending on the species involved, be serious agricultural pests. Some of the crops they attack include maize, pineapples and potatoes. However, there are many species that are of no economic significance and because the species tend to look rather similar it takes a specialist to identify the pest species from those that can be problematic.

Beetles can usually be easily separated from most other insect groups as the adults have strong wing covers called elytra. These are just modified front wings that serve to protect the far more delicate hind wings when the beetle is not flying. Flight is the function of the hind wings, which have a much larger surface area than the elytra and thus need to have the capacity of folding up so they can fit under the protective front wings. The elytra always meet down the centre­ of the insect’s back and this characteristic is very useful when trying to determine what makes a beetle a beetle.

Cicadas, also known as Christmas beetles by most KZN residents, are very different. I have written about these bugs before, so will not spend much time on them. These are essentially diurnal (day-active) insects that feed by sucking sap from plants. They do this with highly specialised mouthparts that are long and thin and are used to bore into plants. Like the scarab larvae, the immature stages, known as nymphs, live underground where they suck sap from plant roots. There is no pupal stage, the nymphs having a rather similar appearance to the adults except for the obvious difference of lacking wings. I was fortunate to find a freshly emerged adult next to the recently vacated skin of its last nymphal stage and, to remind you of what these things look like, include a photo of it. What a wonderful world we live in — let’s do all we can to preserve it.•

Dr Jason Londt is a natural scientist with a special interest in entomology. He welcomes queries and comments, which can be sent to him at [email protected]