Processional Caterpillars

Ochrogaster lunifer

A few years ago we came across what we thought was a metre long, hairy snake. Closer inspection revealed that the snake was in fact a line of caterpillars. We also found two more processions. Each procession was about 50 centimetres long.

The insects are Ochrogaster lunifer. Processionary Caterpillars or Bag-shelter Moths are the common names.

Processionary Caterpillars are found throughout coastal and inland Australia. They feed on acacias and rarely on eucalypts. The caterpillars in our processions had travelled from a large Acacia implexa. The caterpillars had processed at least 200 metres from the tree.

Ochrogaster lunifer have an interesting life cycle. Female Bag-shelter Moths have a wing-span of about 6.5 centimetres. Males are smaller. Wings of females are brown with small white spots on both forewings and hind-wings. Males are similar but may have two to four white streaks on the forewings. The female’s abdomen has a large white, bulbous tuft at the end. The tuft is made up of a tightly packed mass of white scales. A single batch of 150-500 eggs is laid between October and November at the base of acacias. The female moth then covers the eggs with a thick coating of scales from the tuft on her abdomen. This creates a white egg mass about three centimetres in diameter. More than one female will often lay eggs at the base of the same tree. This may be dependent on the density of acacias in the area where moths are active. The tiny caterpillars, that hatch, remain in the egg mass without feeding. After the second time they shed their skins they leave the egg mass and commence feeding on the acacia foliage.

Young caterpillars feed during the day and retreat to the base of the tree at night. More mature caterpillars have a reverse feeding cycle. They nest during the day and feed at night. A stocking-like nest of silk is formed at the tree base. During summer the nest becomes rather large and is filled with droppings, shed skins and hairs. Caterpillars from different batches amalgamate and a single nest may contain up to 600 caterpillars.

This large number of caterpillars may defoliate the whole tree. We had an example at Yallaroo when a colony of Processionary Caterpillars defoliated one of our Acacia neriifolia trees. After a month or so the Wattle recovered and is now bigger and better that ever.

Mature caterpillars are brown, about 40-50 millimetres long and covered with long, extremely irritating hairs.

In May the caterpillars are fully grown and leave their nest. They crawl away in a long procession that may break up into smaller groups. The caterpillars may travel long distances before burrowing into the ground. Each caterpillar forms a silken chamber in the ground before pupating. The chamber incorporates their long, irritating hairs.

Adult moths emerge in late October. In each area the moths emerge within a few days of each other.

PLEASE NOTE: Do not touch the moths, caterpillars or their nests. Their hairs are extremely irritating and may cause long-tern dermatitis and other serious skin conditions. Pets may also have negative reactions if they have contact with caterpillars or nests.

By Warren and Gloria Sheather