Beetles!

Skyrail Nature Diary: March 2015


This month we will be looking at beetles, the single largest group of insects in the world! There is an estimated half a million or more species of these insects, Charles Darwin is quoted as having said that God must be inordinately fond of beetles. Clearly beetles are very successful. So what is their secret? In all likelihood their secret for success is their generalised body structure. A generalised animal is much better at adapting to changes in the environment. Their jaws are very basic with two strong mandibles for chewing, two maxillae for handling food items and a labellum, a movable plate that protects the other mouthparts while retaining some handling abilities. The wings are the most unusual thing about beetles. The front pair has been transformed into two armoured sheaths known as elytra. These elytra protect the vulnerable hind wings which are used for flying. This requires the elytra to fold away to expose them which has both advantages and disadvantages. The advantages are obvious. Who wouldn’t want some light armour? The trouble is, this makes any flying a rather clumsy affair. For this reason, any beetles involved in pollinating require a large unspecialised landing platform that allows them easy access to the nectar and pollen. This kind of flower is actually the most ancient still in existence and the fossil records show, that the earliest flowers were indeed of this simple type. Cycads are the most primitive plants that still use beetles for pollination. It is worth noting that the majority of beetles are less than half a millimetre in length. When rainforest trees are fogged, these tiny beetles are by far the most common animals collected. As for what beetles eat the answer is simple, just about anything. There are beetles that eat engine oil!

Christmas Beetles are very common Australian beetles that often turn up around Christmas. So where have they been in the mean time? Well, all beetles have a complex life cycle involving eggs, larvae, pupae and imagoes. Imagoes are the adults and the pupae are a transitional form between the larvae and the imagoes. The pupae are usually defenseless and therefore hidden away. The larvae of beetles is generally known as grubs and many of them live underground. Most beetle grubs have no protection except for a hard plate on the head. When a suitable victim pass by the grub's burrow, they pounce on it and devour it. The hard plate protects the grub from hungry passerbys. Christmas Beetles are Scarabs, an important group of beetles that were sacred to the ancient Egyptians. Christmas Beetles are clumsy fliers and are generally coloured metallic green or yellow.

Rhinoceros Beetles are among the largest beetles in the world, although not quite in the same league as the Goliath Beetles of Africa. The name refers to the males of these beetles who have a large horn on their backs between the wings and the head. These horns are for display. The horn of the closely related Australian Hercules Beetle is forked toward the front. The females of both species are smaller and look like normal black beetles. The grubs are quite large and are often seen about the place after heavy rain. This is due to the fact that the grubs live underground in a large burrow. Rhinoceros Beetles are a kind of Scarab Beetle and there are many species throughout the tropics. The imagoes of these beetles hiss when threatened but are completely harmless.

Click Beetles are quite unusual beetles. They are moderately long with an unusually large carapace between the head and the wings. This carapace is important with regards to a most unusual kind of behaviour exhibited by these fascinating beetles. Most beetles struggle to turn themselves the right way up if they are turned onto their backs. Click Beetles have an ingenious solution to this problem. The carapace has elastic attachments that can be loaded like a spring when the beetle arches its back. When the resulting tension is released, the beetle is flicked into the air with a clicking sound. If this first click does not result in landing the right way up the procedure is repeated until success is achieved or a bird shows too much interest in this lunch item.

by Tore Lien Linde

 

Christmas Beetle image courtesy of Wet Tropics Management Authority