Bag worms: weird creepie crawly raises intrigue
Males develop into free-flying moths while females remain forever trapped by their bag. She remains wingless, eyeless and legless!
Nature offers us an array of the weird-looking creepie crawlies, often too small to be noticed by the human eye.
I discovered on such wonder last week – an odd-looking worm dragging its house along behind it – and called upon Simbithi etymologist, Graeme Leslie, to explain.
Commonly called bag worms, the larval-stage worm was discovered to be part of an interesting group of moths called Psychidae.
“Both male and female larvae (or caterpillars) make a silk lined casing, to the outside of which they attach pieces of twigs or plant debris forming a bag like tube which they carry round with them as they feed.
“This is the stage that we see in our gardens on trees or shrubs. It would seem that carrying a bag around would make life difficult, however if the bag worm is attacked by a predator, they simply retreat into the bag and wait till its safe to stick their head out again and start feeding,” said Leslie.
Males develop into free-flying moths while females remain forever trapped by their bag. She remains wingless, eyeless and legless!
“How then do they mate?” Leslie asks…
“The female adjusts her position in her bag so that her posterior is at the opening. The male moth flies around – after leaving his bag – in search of a scent trail released by the female moth. However he doesn’t have long, as he has no mouth parts and cannot feed. As soon as a female is found, they mate through the bag’s opening.”
The female immediately starts laying eggs – a thousand or more – inside her bag.
These typically develop over a 2 month period and once developed, larvae hatch and leave the bag using a silk thread to catch the wind.
From here on, the larvae start feeding on plants for about 6 months until they pupate and emerge as moths in the spring and mate.
Most farmers would already be familiar with a different species of the bag worm, the Wattle bag worm, which are a destructive pest to farmers working with wattle, particularly in the Midlands.
These are however not the same species.
