Question of the month

High rise living

What is this bag hanging very high up on the side of a building in the middle of Brisbane? I have attached a photo taken from a distance and a close-up image.

Answer

Saunders’ Case Moth, high on the side of a building. Photos by Katie Hiller and Steve Wilson. Saunders’ Case Moth. Photo from the QM Image Library – Jeff Wright. Case Moth larvae. Photo taken by Bevyn Cornford.

The ‘bag’ you have spotted belongs to the caterpillar of a Saunders’ Case Moth, Metura elongatus.

These larvae can live for over a year and travel long distances, hauling their mobile shelters behind them and feeding on a wide variety of plants. They enlarge these silken shelters as they grow, and add chopped sections of woody stems to their outer surface. When ready to pupate they sometimes hang up in unexpected places a long distance from the plants they feed on. They are often spotted on the sides of fences and buildings, but the larva in your photo has gone to extreme heights! Luckily, their strong silk cases are well anchored and protected from predation and fluctuating temperatures.

If a male moth emerges he will fly away in search of a female. If a wingless female moth emerges she will spend her short life inside her shelter signalling with attractant chemicals called pheromones, waiting for a male to find her. He will mate with her through the opening at the bottom of the case. Females lay thousands of eggs inside the case and the tiny hatchling larvae escape on strands of silk to begin constructing their own shelters.

Although large Saunders’ Case Moths are frequently encountered in gardens we know very little about their early stages.

Recently we received another interesting photo via our Inquiry Service showing dozens of tiny case moth larvae on the move. We believe these larvae are in the same family as the Saunders’ Case Moth, Psychidae. However without rearing these tiny larvae to maturity we cannot confirm this. Unfortunately, the larvae had dispersed by the time we contacted the photographer.

More information about these remarkable larvae can be found in our Fact Sheet.

Want to know more? Our Discovery Centre is a free service open seven days a week, with experts ready to answer your questions. You can phone, write, contact us via our website, or just pop in.

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