Caterpillar of the Common Bag Moth (Liothula omnivora)
Family Psychidae (Sack Spinners)
Species: L. omnivora
Binominal name: Liothula omnivora
Synonym:: Liothula omnivore, Liothula omnivorae
Common names: Common Bag Moth, Common case moth, Bagworm moth, Pu A Raukatauri, Whare Atua, Kopa, Kopi
Liothula omnivora is a native moth that occurs throughout New Zealand.
The nocturnal adult male is a hairy black moth with a wingspan of 28-38 and is the only moth phase. The adult female is not a moth but a wingless maggot (>25mm in length). The female never leaves the bag that she made as a caterpillar and is fertilised by the male moth inserting the telescopic tip of his abdomen through the opening at the narrow end of the bag. The grub like female then lays her eggs and dies.
The eggs in the bag hatch and emerge and climb over the host plant. After a few days the caterpillar spins a bag around its self with silk and bits of vegetation. This very strong tough cylindrical bag (>80 mm long and > 9 mm in diameter) is dragged around by the caterpillar within it.
The caterpillar has three pairs of legs on the thorax (visible in photo below) and five pairs of "prolegs" on the abdomen; these prolegs have numerous hooklets which hold the caterpillar firmly on to the inside of the bag. Using its thoracic legs it can move around, usually at night.
It can also let itself down, bag and all, from branch to branch by silken threads. The caterpillar can withdraw inside and close the bag, it will do this during the day or if alarmed.
Pupation usually occurs during the winter. In spring and early summer only the male pupa forces the front part of its body out the narrow end of the bag. The front end of the pupa then splits open and the male moth emerges. The female pupa stays inside the bag.
The caterpillar of this moth feeds on a very wide range of native and exotic broad-leaved and coniferous shrubs and trees.
Though listed by the Forestry industry as a pest, they state that caterpillars are rarely numerous enough to cause noticeable foliage damage. The only record of appreciable defoliation of Pinus radiata was in Glenbervie Forest, Northland, in 1955. Liothula omnivore caterpillars are heavily parasitised and well controlled by the tachinid flies Pales feredayi and P. marginata. Eggs laid by these flies on foliage are swallowed by the caterpillar and hatch in the digestive tract. The larvae migrate through the gut wall, feed on body tissues, and when the host dies leave the body and pupate inside the bag. As many as 27 flies have been found within a single bag.
Thanks to New Zealand Farm Forestry Association for information on this moth.
The black hairy adult moth Liothula omnivora
Liothula omnivora bag with pupa inside.
Caterpillar photographed climbing wall before sealing itself in. It is attaching the case to the wall.