As I am in the habit of wandering around my yard early most mornings and evenings, I am aware of some of the hidden happenings and subtle changes in my garden. No doubt there are a multitude of lives and deaths overlooked literally under my feet and in front of my nose, but my keen eye for detail often unearths wonderful surprises. The caterpillar of the Dainty Swallowtail Butterfly was one such beauty.
Dainty (or Dingy) Swallowtails, Papilio anactus, belong to the Papilionidae family and lay their eggs on cultivated citrus and a few native species including wild lime and orange, and are common over eastern mainland Australia and southern South Australia. My young orange tree was struggling to survive, so when I found grubs on it I was tempted to dispatch them.
But how could I dispose of such an impressive caterpillar.....
At first sight a caterpillar might appear to have countless legs. But a caterpillar is an insect and therefore has only six true legs. Notice in the image above the three pairs of black legs under the thorax behind the head on the right-hand side of the caterpillar - these are the true legs. The orange suction-looking buds under the abdomen are not legs, and nor are they suckers, but clusters of minute hooks which assist with walking.
And have you ever noticed countless caterpillars on a shrub but yet the bush next to it appears grub-free, and wondered why they choose to eat one plant species rather than several? Throughout evolution, some butterfly species have developed mechanisms to isolate and concentrate noxious chemicals in their caterpillar bodies. Some female butterflies searching for host plants upon which to lay their eggs, are attracted to plants which provide specific noxious chemicals to their caterpillars.
The Dainty Swallowtail caterpillar feeds on citrus, and secrets a nasty-smelling fluid from glands behind the head when it is threatened or disturbed. This secretion smells like decaying citrus.
Butterflies also advertise their distastefulness to preditors with brightly coloured wings. Butterflies fly by day, so need a deterrent to would-be preditors, whereas moths mostly fly by night and are more dully coloured. The chrysalis that houses the pupating butterfly is motionless and therefore relies on camouflage as its only defense.
The top caterpillar begins its final moult, while the lower two are now pupae.
The caterpillar will shed its skin 4 or 5 times in order to grow. Before the final moult, the caterpillar attaches itself to the host plant with silk and then sheds its skin to reveal a different skin which hardens into a pupa, or chrysalis.
The pupa attached to the orange tree blends into its surroundings, while the other caterpillar pictured did not survive the pupating process.
Caterpillars focus their energy on eating and growing. They have strong mandibles for chewing, and most are nocturnal feeders remaining motionless on the host plant throughout the day. They can not mate or reproduce.
Butterflies focus their energy on spreading out and reproducing. Most butterflies only live for about 2 weeks, so they do not have time to waste.
Butterflies do not have teeth or mandibles, but have a coiled proboscis which, when unrolled, acts similar to a drinking straw for probing flowers and sucking up nectar. Their brightly coloured wings will aid in finding and attracting butterflies of the same species.
When a mate is located and accepted, they will face opposite directions and mate end-to-end with abdomens joined. The female will then search an appropriate host plant on which to lay her eggs.
As my gardens become established and my shrubs and trees mature, I hope to provide habitat for many butterfly larvae. If you are lucky enough to see a chrysalis hanging in your garden, you too can feel satisfied that you have provided habitat for the continuing life cycle of a butterfly. Here is a good site (although not Australian) for children to check out butterflies and their life cycle.
The life cycle of a butterfly is a remarkable and complex process. I hope my brief and simple explanation might inspire tolerance for garden grubs. Most will not do irreparable damage to your plants.