Famous for their mass migrations, and notorious for their adverse medical effects, these caterpillars are found over most of Australia. Would you be able to recognise a processionary caterpillar?
Common name: Australian processionary caterpillar
Scientific name(s): Ochrogaster lunifer (Family Notodontidae). However, it is possible that it’s actually two or more closely related species.
Other common names: Australian bag-shelter moth, ‘itchy grubs’.
Geographic distribution: Found in all states and territories of mainland Australia.
Description: The caterpillars grow up to around 4 cm in length, a reddish brown head capsule, nine black bands around the body, and are covered in long grey or brown hair. Their processionary behaviour and ‘bag’ building habits (described below) are key identifying characteristics.
Adult moths have a 4-5 cm wingspan. They are brown and may have white spots or bands on the wing with long fur on the thorax and tip of the tail. The abdomen is banded in yellow and may be revealed when the moth curls into a defensive posture and plays dead.
Habitat: Most common in open forests and grasslands with suitable host trees and shrubs.
Life-cycle: Ochrogaster lunifer has a one year life-cycle. The adults emerge from their pupa in the leaf litter in spring. After mating the female lays up to 500 eggs in a mass on the trunk of a suitable food tree (such as wattle). The caterpillars hatch after a a couple of weeks and then start feeding. The caterpillars construct a communal nest (bag-like in appearance) that the caterpillars return to after feeding. The bag gets bigger as the caterpillars develop. They go through 8 instars before pupating. When they are reading to pupate they leave the bag in Autumn and will form processionary lines of up to 200 caterpillars as they try and find a suitable underground location to overwinter. In early spring they form a pupa to develop into the adult. The caterpillars will also form processionary lines if they defoliate a tree and need to find a new food source.
Medical attention should be sought for any reaction to the hairs.
Pest status: Both caterpillars and adults possess abundant microscopically barbed, fragile hairs that can easily penetrate skin. These hairs are all over the body of the caterpillar, and concentrated on the feet and end of the abdomen of the adult.
The oldest caterpillars carry over two million irritating hairs, which can cause serious skin rashes, conjunctivitis and other allergic reactions in sensitive people, when they come into contact with the skin or are inhaled. There is also risk of the caterpillars or their hairs being eaten by a toddler or pet. The reaction is to proteins on the hair, after it has penetrated skin or mucous membranes. These hairs may be found anywhere near infested trees, especially after the caterpillars abandon their shelters, the silk begins to break down, and loose hairs are scattered over the surrounding area.
However, the effect of the hairs on livestock can be worse – the caterpillars’ hairs have been connected to spontaneous miscarriage in horses. It is suspected the hairs puncture the gut lining after being eaten. An outbreak in 2001, caused by the unrelated eastern tent caterpillar, Malacosoma americanum (Fam. Lasiocampidae) devastated Kentucky’s thoroughbred breeding industry.
Heavy infestations can easily defoliate small trees and shrubs. Use of a whipper-snipper around the base of a tree can tear open a bag-shelter and scatter millions of hairs into the air.
Treatment: No insecticides have been approved for control of the caterpillars. Eggs and younger caterpillars are eaten by a range of native parasitic wasps and flies, and Trogoderma beetles. These can control caterpillar numbers to a degree.
Caterpillars and moths should not be handled with bare hands. The Bag-shelter nests can be removed from gardens manually, if full protective clothing is worn, and care is taken to not inhale the irritating hairs, or expose eyes or skin.
If a procession enters a garden, they can be swept into a garbage bag and discarded. If the caterpillars are believed to be pupating among leaf litter, the leaf litter can be raked up and composted, although hairs will continue to be a problem.
Other caterpillar pests.
Daniel Heald, technician and entomologist
Image credit: Adult moth by Donald Hobern – Flickr: Ochrogaster lunifer, CC BY 2.0