Ever wondered what it's like, living in a bag? There are many different species that live in bags or cases for prolonged periods of time and the cool thing is, they make those bags themselves. Silk appears to be the material of choice in the majority of bag-builders. That silk can be really strong too.
One of the most obvious (up to 80 mm long) insects that shows off its bag in our garden is the native bag moth (Liothula omnivora). They are often found hanging from conifers and hebes, flaxes, tea-tree, willow, cherry, you name it. Their grey cases don’t really move much during the day, but at night the inhabitants cruise the foliage and nibble; creating holes.
The bags are constructed “as they go and grow”. Crossed layers of sturdy silk: impenetrable! They also add “camouflage” to the bags: pieces of dead foliage, twigs and other locally-found materials. That can include bits of plastic bags or psychedelic coloured post-it notes (young scientists experimenting with drugs!).
The cases protect the caterpillar and also do well as a pupa cocoon for metamorphosis. Their lifecycle is like most Lepidoptera, but females (when they hatch from the pupa) are wingless and flightless and are fertilised by the male moths inside their cases. Males are black and fast-flying moths that detect females via pheromone scent.
But the craziest bags around (especially in the North Island) are the pieces of “dirt” that hang from walls, rocks and tree trunks at this time of the year. They are merely 20 mm long and have that untidy look that won’t get them any prizes in Fashion Week. This is the time of the year when they are most commonly seen. These silk bags are adorned with bits of dirt and lichen, wood and grains of sand. Inside, live caterpillars of an Australian moth species by the name of Cebysa leucoteles. It’s a critter that came across the ditch in the nineteen seventies or so, possibly on some agricultural machinery destined for MOTAT museum in Western Springs, Auckland. Cebysa is not like our native bag moth; it does not feed on foliage and it does not leave holes in leaves. Instead, it roams around mouldy old wood and green, algae-ridden trellises or south-facing walls and soffits, covered in slime, moss and algae. Cebysa is the living, breathing and reproducing version of “Wet and Forget”.
The adult moths are around in March and they look quite amazing: males: orange brown and fully winged Females are most iridescent blue and bright orange. Their wings are “distorted” and shaped like the elytra of ladybird beetles. They can’t fly at all, but often are found walking fast over pavers, decks and garden soil. Like running jewels! And in the middle of the day! Males will track them down to mate with them. Look out for them, especially in the Auckland suburbs and further afield.
LISTEN TO AUDIO ABOVE