Have you ever spied a large, leathery cocoon constructed with small sticks, all attached lengthways with seemingly deliberate care? Often found hanging from tree-trunks or fence palings, these are bagworms that may be encountered in the Illawarra and surrounds.
But these creatures are not worms at all, in fact, they are moths.
The Saunders’ case moth, Metura elongatus, is a common species along the east coast of Australia. I have often found this species creating their cocoons using the needles (or branchlets, if you want to get technical) of the casuarina trees that proliferate around the briny waterways of Lake Illawarra.
As a child, I imagined these cocoons were vessels for the transformation of some gigantic and beautiful butterfly. In actuality, the larvae are the main event, living for up to two years in their silken cocoons. And the adults are not particularly attractive. In fact, the male look like a large, elongated tiger moth… who’s been stretched and then dragged through a bush, backwards. They look like the Kogan-version of a tiger moth with wings that seem a little too small for its body, a fuzzy orange head and thorax, and a tufty black and orange body.
After hatching, larval bagworms immediately begin crafting their cocoons from silk, attaching leaves and sticks as they go. The cocoon is continuously expanded as it grows and becomes a protective mobile home for the long-lived larvae. They are plant feeders whose heads and legs protrude from the end of the cocoon to feed and climb as they drag their house behind them.
The case is surprisingly strong and provides natural camouflage against predators. When threatened, the larvae simply shut up shop by sealing the top end of their case until the threat passes. The larvae carefully embellish their cases, selecting each stick or piece of debris with care. Once selected, the piece is temporarily adhered to the outside of the case while the larva makes a precise incision in the case’s silk, making a hole where they wish the adornment to reside. The larva then pulls the stick through and weaves the hole shut, keeping the prized piece of detritus in place with impressive toughness.
You'd better believe that nature’s tiny homes also come with a fully functioning toilet. This comes in the form of a small slit in the casing near the tip, furthest from the head-end, where the larvae deposit their waste, like an inbuilt poop-chute.
After an impressively long childhood in their homespun houses, the larvae attach their abode to a substrate, seal it and then pupate. If the case moth is male, it emerges from the case after pupation and lives only long enough to find a female and mate.
It’s lucky they have long larval lives because the life of an adult female is even more deflating. The adult female does not leave her case, as she is wingless and also lives only long enough for a winged male to find her and fertilise her eggs. She then crawls out of her case to die, her final act being one of maternal sacrifice.
She leaves her protective home in order to attract a bird in the hopes that she will be eaten. This ensures that the hard-cased eggs inside her body and thus her genetics, are distributed more widely, as they get pooped out wherever the bird goes, much like a seed.
Being a mother myself, I can’t help but sympathise with the female bagworm, sacrificing her body in posterity for her offspring. Heck, I only wish I was in possession of a camouflaged tiny-home, in which to hide from said offspring occasionally. I think I’ll start using bagworm as code to alert others to my need to retract into a cocoon of silence and seal it shut. Whether it’s within a sleeping bag adorned with sticks found in the backyard, or behind a locked bathroom door with ear plugs, retreating into the foetal position is a tried and true method for combatting the overwhelm of maternal sacrifice.
