Following on from my last post about the arachnids of Zimbabwe, I wanted to write something regarding the plethora of exciting beetles found here too. I know beetles are usually the favourite subject of that weird kid in class who caught them in nets and spent hours painstakingly pinning them delicately to a board, and Beetle enthusiasts are often shown in films as the charismaticly challenged guy with pocket protectors and bad acne – but stay with me here and hopefully I can convince you that these usually gentle creatures can be fascinating. Before we begin though, it’s worth me explaining what a Beetle actually is.
We’ve already looked at arachnids; so what makes a beetle so different? Beetles are insects, arachnids aren’t. Arachnids have two body parts (a cephalothorax and an abdomen), eight legs, and are all wingless. Insects have three body sections (a head, thorax, and abdomen), two compound eyes and two or three simple eyes, antennae, and six legs. Most insects also have two or four wings, and they develop in stages of metamorphosis – a young arachnid still, generally speaking, looks like an adult arachnid, compare this to a caterpillar becoming a butterfly.
Beetles are insects from the order Coleoptera (which translates approximately to “sheathed wing“) usually with four wings. Thr first set of wings are hardened into what is called an elytra, a wing-casing. The order Coleoptera has more life-forms in it than any other, with beetles making up approximately 25% of all known animal life-forms. Beetles also make up over 40% of insect species, and new species are being found constantly.
I feel it’s best to start at the grandest I’ve seen here, the Longhorn Beetles, members of the Cerambycidae family. These beetles are characterised by their long, flexible antennae. The name Cerambycidae comes from a Greek myth where a shepherd, Cerambos, had an argument with a nymph and was turned into a large beetle with horns.
These beetles are often considered pests as they lay their larvae, called roundheaded borers, bore into trees and untreated lumber and can cause extensive damage. Both the larvae and the adults eat wood (with adults often taking rotten wood and leaf litter) hence the well developed mandibles.
Longhorn Beetles come in a variety of shapes and sizes, and each has its own preference on wood – with some species being exceptionally fussy and will only be found in areas with certain trees being endemic. Despite their size, Longhorn Beetles are primarily harmless – having no stings or chemical defenses. Although the mandibles are of daunting size, it’s difficult for the beetle to angle them severely enough to actually bite and they tend to be of a very docile temperament. If their chosen diet-wood is readily available they make surprisingly hardy pets.
The Giant Longhorn Beetle shown above is a known predator of Marula, Wild Plum, and Cashew Nut trees, the Large Brown Longhorn is a predator of Acacia, Citrus, and Ficus.
Of course, not all Longhorn Beetles are of such impressive size. Others, like the Dumpy Longhorn Beetle above, are a much smaller size. Unlike the Giant Longhorn species, the Dumpy Longhorn has a rough, almost spiky elytra with beautiful mottled markings that camouflage it well to the fig trees which it feeds on.
Dung Beetles (Scarabaeidae) are another common sight here in Zimbabwe, and are easily recognisable due to their large shovel-like heads, rounded bodies, and strong rake-like legs. Most, but not all, feed on dung, and most (but again, not all) lay their eggs inside a dung ball. Dung Beetles will grab a ball of dung and roll it, using their strong hindlegs, directly back to their nest, regardless of obstacles. They are the only non-Roman animal known to orient themselves using the stars.
As with most families of beetles, dung beetles come in a variety of shapes, sizes, and colours. Some, like in the first picture, are large and dull in colouration (though there are some species much larger than this one), whereas others (like above), come in pretty copper or brand colours or even vibrant greens and yellows. Most dung beetles can roll a dung ball more than 10 times their own bodyweight, and many are known to intercept and steal dung balls from other ding beetles.
There’s a sub family of Dung Beetles known as the Rhinoceros Beetles (Dynastinae), some of which look very similar to normal dung beetles and share similar behaviour. Rhino Beetles are easily recognisable by their large protruding “horns” and like all dung beetles, are completely harmless to humans. Their horns are most often used for Burrowing and for fighting competitor males.
Some, like this Rhino Beetle, do not have the characteristic shape of a Dung Beetle, and instead feed on wood and can fly (though not very gracefully), tending to be nocturnal. With their impressive size, easygoing nature, and surprising longevity (sometimes more than three years for adult males) they make fantastic pets.
Of course, not all beetles are quite so placid. Some Ground Beetles (family Caribidae – named Ground Beetles as most have fused elytra rendering them unable to fly) are docile and harmless, but many, like Passalidius fortipes (Burrowing Ground Beetle), are not. When trying to take the above photo, this little one repeatedly scuttled towards me, rearing up with it’s mandibles wide open as if it meant to bite me. The Burrowing Ground Beetle is an adept burrower, using its strong forelegs and mandibles to hunt insect larvae and worms through the ground.
Admittedly, the bite is nothing dangerous, beyond the minor mechanical injury, but the Caribidae have other tricks up their sleeves, or rather, up their abdomen, in the guise of pygidial glands that produce noxious or even caustic secretions.
These chemical weapons give many Ground Beetles another common name – the Blister Beetle, but true Blister Beetles are from a very separate family, the Meloidae. Blister Beetles get their name from the cantharidin they secrete, a toxin that causes blistering of human skin and is toxic if ingested. Most Blister Beetles announce their toxicity through colouration.
Despite their toxicity, Blister Beetles are often beneficial to have around. The larvae of the CMR Bean Beetle (so named for the colours being those of the Cape Mounted Rifles Regiment of South Africa) for example parasitizes the egg pods of various grasshoppers, including Plague Locusts, helping to regulate their numbers. However, the adults feed on plants and are known to damage ornamental garden plants, and cotton, beans, peaches, and other crops.
At this time of year, I would be remiss to not mention the Rose Chafers, also known as Rose Beetles, or Christmas Beetles. These cute little fellows appear all over the place at this time of year (I suppose it’s their breeding season) and they’re attracted to lights, so they’re often seen relaxing on screen doors, computer monitors, and most annoyingly, our bed. They are completely harmless, but they are dopey fliers and so it’s common to be sitting watching a film in the evening and having several chafers bashing into your face as they excitedly make their way towards the screen. They’re nocturnal and feed on flowers and foliage of wattle, potato, and sugar cane, though they seem to have a favourite in garden roses, hence their common name. Despite their appearance, they are actually members of the Scarabaeidae family, though they do not feed on dung balls, or lay their eggs in them either.
I’ll round this all up with an honourable mention to the Cicada. The Cicada are members of the Order Hemiptera, the “True Bugs” (you see, “bug” and “insect” aren’t synonyms, a “bug” is a very specific type of insect, but more on this some other time), whereas beetles are members of the Order Coleoptera, as you now know, but for some reason, the Cicada is often (erroneously) called a Cicada Beetle.
I’ll go into the reasons why in a future “bugs” post, as I will give a proper description of the Cicada, but for now, suffice it to know that “Cicada Beetles” aren’t beetles, and should simply be called Cicadas. Then you’ll be correct and it’s less effort to say!