Bugs and Grubs By Sue Hasenpusch:

Reproduced from the Wet Tropics Newspaper with their permission

To many avid gardeners the sight of a caterpillar chewing on a favourite garden plant will have it labelled pest with a capital 'P'. Other people are alarmed when they find big fat grubs in the backyard, and worry that they may harm the garden. What are those creatures chewing on leaves or crawl-ing in the compost heap? In most cases they are the larval stage of the very same insects we enjoy having in the garden.

They are the butterflies that feed on nectar and pollinate flowers in the garden, or the beetles flying around the house light at night.

Baby Butterflies

The most commonly encountered larval stage of an insect is the butterfly caterpillar, usually found eating the leaves of many backyard plants, both native and exotic.

A citrus tree in the backyard is a prime host for the larvae of one of our largest butterflies, the Orchard Swallowtail (Papillio aegeus). Caterpillars of the Orchard butterfly are easily recognised. In the early larval stages they resemble a white and olive-black bird dropping.

The larger larvae are a camouflage green and brown, enabling them to blend with both the leaf and bark to avoid being eaten by birds. These larvae also have what resemble 'spikes' along their body, but they are soft to touch and completely harmless.

Like most butter-fly larvae, when disturbed they extrude two bright reddish horns from their heads which emit a strong odour - another useful defence against predators, but harmless to people. The pupa or chrysalis stage of the Orchard butter-fly can be difficult to detect on the tree due to the two colour forms of either total-ly green or green and brown camouflage, depending on their position on the tree.

Adults usually emerge from the pupa in around 4 to 6 weeks. Both male and female Orchard butterflies have distinct markings, making identification easy. The male is generally black with a narrow white band across the forewing while the female ahs a large pale forewing and hindwing. A more obvious feature is a row of red spots around the edge of the hindwing.

These adults will in turn frequent the garden insearch of their food supply, provided by the nearest flower.

Grubbing About

What about the grubs we find when digging in the soil or compost heap? The largest grub most commonly found in the garden is the Rhinoceros beetle grub (Xylotrupes gideon), also sometimes called the Elephant beetle.

Easily identi-fied, this translucent creamy - white larva has fine reddish hairs with a dark brown head capsule and can grow up to 80mm long. Such an enormous size is reached through a diet of decomposing matter, which makes the backyard compost heap a popular breeding site. Larva feeds upon the organic matter until fully grown, then forms a cell in the soil in which it turns into a pupa.

After around 6 to 12 weeks the adult beetle will dig its way to the surface and take flight. Considered one of Aus-tralia's most spectacular beetles, the stout black Rhinoceros beetle can reach a size of 65mm. Male Rhinos are easily identified with their armourment of forked horns on their head and thorax.

Horn size is important when engaging in 'fighting' mode. Female Rhino's emit a scent to attract the males, and often more than one suitor arrives. When two males meet around a female, battle is instigated using the horns to butt and toss the other contender away, with victory usually coming to the larger male. While these horns look daunting they won't hurt humans, only producing a weak pinch.

The Rhino beetle is often accused of biting, perhaps on the toe as we walk through the grass at night.As with most beetles the Rhinoceros beetle has biting mouth parts to feed, but these mouth parts are so small they pose no threat to humans. What is being confused with a bite is actually the beetle grabbing tight with its hook-ended legs.

These hooks help the beetle when climbing, digging and mating. Most people's reaction is to pull the beetle off, which unfortunately encourages a tighter grip. Removal is much more easily obtained by gentle persuasion. Both the female and male squeak or hiss loudly when disturbed or handled. They make this sound by rubbing their abdomen against the ends of their wing covers.

Although the Rhinoceros beetle flies all year round, they are usually seen more frequently during the summer months around a house light or under a street light. Sometimes a group of Rhino beetles can be seen in Poinciana trees, and they are also found in fruit such as paw paw, which they only enter after a marauding bird has pecked a hole in the fruit.

Generally, the larval stage of insects fulfil several roles in the garden. When chewing on some of our favourite garden plants, butterfly larvae are part of a natural pruning process for the many trees, vines, shrubs and other plants that insect larvae use as their food plants.

As for the grubs in the garden and the compost heap, they assist in the decomposition process by returning dead plant material to the soil and aerating the soil - a major component to any healthy garden.

End.