Ribbed Case Moth

by Kate C
Publish date
4 October 2013
Comments (4)

Working at a museum can extend the joys of ‘show and tell’ far beyond its usual primary school lifespan. Recently I brought in a photograph of a cluster of pupal cases for the entomologists to identify. I’m used to seeing the Saunders' Case Moth with its portable log-cabin shelter hanging from fences and walls, but I hadn’t seen these smaller and plumper silk cases before.

Ribbed Case Moth pupae on tree Cluster of Ribbed Case Moth pupae on a tree trunk.
Image: Kate C
Source: Museum Victoria

Entomology collection manager Catriona McPhee identified the critters in about half a second. “Hyalarcta nigrescens, Ribbed Case Moth, family Psychidae.”  (We love it when the entos do that.) I’m told that this species is not uncommon, but the local density of the cases here is unusual.

This cluster of over 60 cases was on the trunk of a lone, spindly eucalypt surrounded by asphalt on Smith Street, Fitzroy. It’s intriguing to think how this population got there in the first place because the females of the species are flightless. When they’re done with metamorphosis, they simply remain where they are and release a cloud of pheromones to draw in the winged males. They never leave their cases, depositing their eggs inside. The caterpillars hatch and wander off in search of leaves to eat and soon build their own cases.

So, if we assume these cases belong to one cohort of siblings, how did their mother get to the tree when it is many metres from other food plants? My money’s on a spot of hitch-hiking; I reckon she was on the tree when it was planted, and perhaps there’s a healthy population at the tree nursery.

Tree growing on city street The cluster of case moths were on the trunk of this small, isolated tree.
Image: Kate C
Source: Museum Victoria

The isolation of the tree might explain why there are so many pupae here. While case moths are mobile and can haul their homes a considerable distance, in this concrete jungle they didn’t have anywhere else to go. They were stuck on the island. So the poor little tree got hammered but it means we have this array of beautifully-built nomadic shelters to admire.

I went past the tree again a couple of weeks later to find a frenzy of emergence. The females were staying put, of course, but many of the cases bore the equivalent of a vacancy sign: a rumpled, shed skin (pupal exuvia) at the end. A couple of the male moths – black, hairy, with glassy bluish wings - were still clinging to their former homes. I think I'll go back and take some of the female cases and try to rear any eggs inside... and give the poor tree a break from a third generation of relentless leaf-eaters!

Ribbed Case Moth pupae on tree A couple of weeks later, the Ribbed Case Moth males were emerging from their cases - you can see a blue-black winged adult at the bottom of this cluster.
Image: Kate C
Source: Museum Victoria


Ribbed Case Moth on Bowerbird

Life cycle of the Ribbed Case Moth (Coffs Harbour Butterfly House)

Comments (4)

sort by
Neroli 4 October, 2013 14:03
Very Cool, Kate. Now I'm going to peer at every isolated tree I pass. Please keep us updated on how your moth rearing goes.
Richard Hayward 4 October, 2013 15:30
I would love to see more eucalypts planted in our streets instead of plane trees to encourage more wildlife like this.
Lesley Haine 3 December, 2013 18:34
Thanks for this info, my parents live at newlands Arm near Paynesville and have a tree totally draped with them. The tree is dying under the load.
James Smith 28 April, 2014 15:52
Thank you, a fascinating story of survival!
Write your comment below All fields are required

We love receiving comments, but can’t always respond.

About this blog

Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.