Beetles

Beetles are beautiful! Many are multicoloured and shiny. However, soil beetles in the area where I collected tended to be rather boringly black (as these photos show) but then they live in the dimmer environment of the soil, litter, dung or rotting wood where colour may have no particular advantage.

Beetles usually have a very hard, shiny outer surface. They have two sets of wings. The flying wings are filmy and are tucked away, protected under the hard upper set of wings or wing covers. They are insects and the adult and larvae mostly have three pairs of legs. Adult soil beetles use their wings for dispersing from place to place but once in the soil, litter, dung or rotting log, use their legs to get about as wings are useless in the confined space of their habitats. If soil beetles have to dig tunnels deep in the soil , their legs and heads are often adapted to form flanges, making them look like miniature bulldozers e.g. dung beetles. Beetles have compound eyes which can be prominent in predatory beetles such as ground beetles. A pair of antennae on the head also help the beetle make sense of its world.

There are many types of beetle that live in soil, litter, logs and dung. The larval and the adult forms can either both live in soil, as in ground beetles. Or the larva may live in soil, while the adult flies off to an above-ground life. This happens with the Christmas beetle where the larva is a large “C” shaped grub living in soil, eating both roots and organic matter, while the adult lives on eucalypt leaves, sometimes decimating the trees in summer.

Dung Beetles

Some “soil” beetles live exclusively on dung. These are the dung beetles. They have an acute sense of smell and can arrive at a dung pat within seconds of its passing from the animal! I have watched a cow pass a dung pat, and within the short time it took me to walk to the pat, there were already dozens of dung beetles buzzing eagerly over it. Dung beetle adults feed on the dung, but then tunnel into the soil under the dung pats. They drag bits of dung into the tunnels, form a brood ball where they lay their eggs and the larvae hatch out in a dung ball, entirely surrounded by their food. After a juvenile life in the brood ball of one to several months, they emerge as adults tunnelling out of the ground to start the cycle all over again. Other dung beetles are ball-rollers. They carve off bits of dung with their forelegs and shovel-shaped head, form a tight ball of the dung and then roll it away from the dung to attach it to a grass stem. They then lay eggs in the dung and the larva hatches into its dung food source.

Ancient history: the sacred scarab of the ancient Egyptians was a dung beetle (whose scientific family name is Scarabeidae). It was a symbol of life and renewal. Egyptian myths have it that the scarab dung beetle represented the god, Ra, who rolled the sun across the sky each day and then buried it at night. Amulets of scarabs such as the one pictured, were worn as protective charms.

If dung beetle activity is high as in summer, sometimes the beetles completely shred and bury the entire dung pat and all that's left is a scatter of dung fragments on the soil surface. At other times, only a few dung beetles are active and you can pick up a dung pat and see the tunnel they have made into the soil.

 

Collecting Dung Beetles

Dung beetles are easy to collect. Find a cattle dung pat which is reasonably fresh (within a week old) and which has some evidence of mini-excavations in the surrounding soil. This means the dung beetles have been at work. Pick up the dung pat and put it in a bucket of water and stir gently with a stick to break up the dung. The dung beetles float to the surface of the water where they can be picked out.

Passalid beetles

Passalid beetles (both adults and larvae) live in rotting wood where the adult chews through the wood, digesting it in their gut and gradually returning the wood fragments to the soil. They are large shiny black beetles up to several centimetres long, and have a short horn in the centre of their head. The wing covers are deeply grooved. The adults tend their young larvae, chewing the wood and feeding the larvae the predigested wood. The passalid beetle larvae have only 2 visible sets of legs – the hind set are shortened to rub against the middle pair of legs to produce sound. This is called stridulation. The adult passalids stridulate by moving the wings against the abdomen.

Passalids are important decomposer animals in forests. Being decomposers, they do not need to move fast and are quite easy to catch when spotted inside rotting timber. Once you’ve found a passalid beetle, keep hunting and you will generally find larvae and pupal cases nearby. I found the one pictured in a rotting pine log.

Rove beetles

Rove (or staphylinid) beetles have shortened wing cases so you can see the banded or segmented abdomen clearly. The wings are intricately folded under the short "bum-freezer" wing cases with the help of their hind legs and tip of the abdomen. Rove beetles are often carnivorous and are very active, fast movers. They feed on living and dead invertebrates, fungi, dung and other organic material. The rove beetle pictured was around 2 cm long. It can curl its abdomen up over its body – probably a defense reaction.

Some rove beetles produce a highly toxic body fluid when disturbed which can cause severe dermatitis, skin irritations and blisters.

Pie-dish beetles

Pie-dish beetles – so-called because the flanges on the edges of their wing covers and thorax look like the edges of a pie dish – are either flightless, or like most other beetles, can fly using their filmy wings. The wing covers are fused in the flightless ones. Wings are a bit of a nuisance in soil insects as they are pretty useless when moving about in soil, litter and dung and are only really used to disperse the animal to other places or for eluding a predator.

One flightless pie-dish beetle occurs in arid Australia where it hides under logs and stones during the day. They feed on organic debris, fungi and bark. One type of pie-dish beetle has what looks like lichen growing on its back, mimicking the mossy, lichen-covered rocks where it lives in rainforests.

Ground Beetles

Ground (or carabid) beetles are generally glossy black, sometimes with a metallic sheen. They are fast moving beetles with long legs which are often found under rocks and logs. They are carnivorous feeding on living and dead animals. Carabids are nocturnal and hunt other soil insects and their larvae, slaters and even snails and tear the prey apart with their large jaws. Other predatory ground beetles apply the lie-in-wait strategy. When you disturb them by moving their log or rock, they are very quick to scuttle off.

Click Beetles

Click beetles are so-named for the sound they make when they are overturned and then flick themselves upright again. The clicking sound is made by a peg on the underside of the beetle which flicks out of a corresponding groove. The beetle can then spring up into the air and right themselves before they run off to find shelter.

Scarab larvae

These large “C” shaped grubs are a great meal for magpies. The adult of this type of grub is the shiny light-brown Christmas beetle which can defoliate eucalypt trees over the summer months. The larvae eat their way through the soil, feeding on grass roots and dead organic matter. If you accidentally dig one up in the garden and it has been damaged, you can see the soil that has been in the gut smeared over your hand. At times, these larvae can become a turf or pasture pest. When they feed on roots, they can cut the entire root system and the turf or pasture can be just picked off the soil.

Flowerwasps

These larvae can become prey to wasps. As with the spiderwasps, a female flowerwasp can find this large larva underground, sting it to paralyse it, drag it into a hole already dug in soft soil, before laying an egg on the grub. The larvae of the flowerwasp hatches and devours the still-living grub.