A great egret looks for breakfast at Calamvale Creek


Scientific stuff

bag-shelter moth caterpillar

Ochrogaster lunifer
Family: Notodontidae
Order: Lepidoptera

Size: Adults 4 centimetres (a little under 2 inches).

Grey and brown hairy caterpillar with about 9 black stripes or bands around its body. Found in groups of up to several hundred on wattle trees, or sometimes eucalypts.

The head is brown. Long grey or whitish hairs protrude from body, and the prickly hairs cause dermatitis or other skin problems if humans touch them.

These caterpillars are famous for their “processions” — dozens or hundreds of them form a long line and follow the leader to a new destination.

When they are fully grown, or when they have eaten all the leaves on their host tree, they head off to find either somewhere to spend winter before pupating, or another tree to dine on.

The moths emerge in October and November, and fly in the early evenings. Like the caterpillars, adult moths can cause rashes and skin irritations.

Congregational. Always found in very large groups. They stick together like a long chain of hairy bar magnets.

Using our photos

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Prickle's photos

Prickle was the leader of a chain of 74 processionary caterpillars that had just left their host tree beside the upper drainage channel at Calamvale Creek.

Our photographer noticed this caterpillar train as it was about to cross a concrete path.

The time was 7:45 on a pleasant mid-April morning. Five days later, on April 19, he saw four more trails of them at the southern end of the creek.

The photographer said:

“It's a spectacular sight when you come across the bag-shelter caterpillars as they walk in a line that is several metres long.

“This line was more than three metres (10 feet).

“The caterpillars themselves are not attractive, and cause terrible skin irritations if you touch them. But you have to admire their amazing instinct and determination to find a new tree or a suitable place to pupate. And they do it in one journey to a place they have never been before.

“They always look as though they know exactly where to go, although they have spent their whole lives in one tree so far.

“This group headed toward a clump of trees with new pine-bark chips at the base of some trees. It was more than 80 metres from their old home.

“They walked in a fairly direct line over rugged terrain, then grass, then sand and soft soil.

“But how did they know where to go? There is some amazing programming in these little critters.”

Another trail

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Above. April 19.
Another trail, another poo pellet to help the stragglers find their way when the thread broke.

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Unfortunately, some stragglers in this group didn't make it, because someone or something ran over them while they were crossing the dirt track.

Critters of Calamvale Creek

Prickle, the bag-shelter moth caterpillar

Ochrogaster lunifer

hairy_processionary_caterpillar_1 (25K)

Hello caterpillar lovers. I'm Prickle, the bag-shelter moth caterpillar. I'm called Prickle because my bristles will prickle you and give you a rash if you touch me. I am on my way to find a place to stay over winter before turning into a bag-shelter moth.

But wait, there's more

hairy_processionary_caterpillars_6 (30K)

I'm not going alone on this journey. We bag-shelter moth caterpillars like company …

A lot of company!

hairy_processionary_caterpillars_3 (33K)There are 73 of my brothers and sisters setting out with me today on our great pupation adventure. You can see our trail in the photo at right. We are crossing a path to get to the grass and sandy soil on the other side, and that will lead us to our winter home among debris on the ground.

It's well into autumn, you see. We are now 4 centimetres long, so it's time for us to start the next stage to our destination of turning into bag-shelter moths in October.

Why are we called bag-shelter moth caterpillars?

We are called bag-shelter moth caterpillars because large numbers of us stay sheltered in a big silk bag at the base of a wattle or eucalyptus tree — or sometimes high up in the tree. We leave the bag to go out and feed on leaves all day (or all night), then come back to it.

If we eat all the leaves on our tree, and are not yet big enough to go to the pupation home, we all line up, single file, and head off to find another tree.

There are only 74 of us today. But we hear stories about hundreds of caterpillars sometimes forming a line. One group of 157 crossed the road at Acacia Ridge to find a new home. Unfortunately, only 141 made it to the other side.

We are determined

We cross over any terrain. We cross over prickly needles …

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We cross over clumps of grass …

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And we cross over sandy soils …

hairy_processionary_caterpillars_8 (36K)You can see our deep trail. When 74 caterpillars march along the same soft track, we're going to leave an impression. This indentation in the soil was nearly one centimetre deep when we had all gone though.

How do we stay together?

As we walk, we leave a trail of silk from the spinneret near our mouth. We walk head to tail following this silk thread.

Sometimes the thread gets broken, and caterpillars near the end of our convoy may get lost for a while, like the guys in the photo below.

hairy_processionary_caterpillars_5 (17K)

But a couple of poo pellets from Oscar helped them get back on track.

The thread is strong

hairy_processionary_caterpillars_9 (47K)Even though the thread breaks sometimes, it is extremely strong.

The photo at left shows our trail (from bottom right to top left) nine hours after we had been through in the morning.

During the day, someone on a bicycle ran over our track, yet you can still see the silk thread (green arrow points to it) up the centre of our trail. The thread was still visible, where the afternoon sun made it sparkle, all the way to our new destination among another stand of trees.

If the weather is fine and the ground is not disturbed much, the thread may be visible for days, or even weeks.

Our old tree home

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Above: Left: This is the tree the caterpillars came from. A brown stocking-like bag full of droppings and shed caterpillar skins has built up on the northern side of the tree where the parent moth first laid her eggs. Each caterpillar moults eight times until it is fully grown. Centre: The caterpillars leave strands of silk down the tree trunk that leads to their silk-bag home at the bottom of the tree. Right: The silk bag to which the caterpillars return each day or night when they have finished eating. It is difficult to see because the silk is mixed with dead leaves, twigs, and ground litter. This bag is about 30 centimetres (12 inches) wide and 40 centimetres (16 inches) long. Arrows point to entrance and exit holes in the bag.

Now that I have found my home for winter, I will make a cocoon in the ground out of my prickly hairs and spend the winter in it. In spring I will turn into a pupa, and finally emerge as a bag-shelter moth in spring (September to November).

When I am a moth, I will still have prickly hairs that will cause itchy skin eruptions and rashes if you handle me or touch my hairs.

— Prickle the processionary bag-shelter moth caterpillar