If you live in Australia, especially on the Eastern side, you may have seen one of these weird cocoons seeming to move by itself across the ground, or climbing a tree. I can remember seeing these for years, but not quite as big as this one. Down South, they are usually about 5, maybe 6 centimetres long. Even the articles online suggest they grow ‘up to’ 15cm. This one is a full 20cm long:
They are made by the caterpillar of the Case Moth Metura elongatus. Well, I think this is that one. There are over 1350 different species of the family Psychidae, with 350 of them native to Australia The inside of these constructions are soft silk, spun by the caterpillar. It then stripes twigs, or even uses sand to protect and camouflage its cocoon.There are many varieties of the Case Moth, with different types using different materials.
The caterpillar builds its case from the head end. So, as it grows bigger, it has to attach more, and larger twigs. These cases a very strong. The twigs themselves are incorporated into the silk by the caterpillar cutting a slit in the inside, temporarily attaching a twig to the outside bforehand. Then they go inside and pull the twig into position from the inside, then sealing the slit again. The process of cutting the slit alone can take an hour. The caterpillar lives in this case for up to Two years. If threatened, they will seal the entrance and wait until the threat passes before cutting their way out of the sealed entrance. The female moth usually continues to use the case after it morphs. However, the males abandon theirs.
I think this one is a work of art. The symmetry of the case and the elegant frill around the case entrance is amazing. I’ve put a lot of images in this post, because there seems to be a lack of good images of these caterpillars around the Web. Maybe a student will see this while researching for a project or something.
The caterpillar looks tough and leathery, but they’re actually quite fragile things.
For a fact Sheet in PDF format, paste this link into your web browser: