Common bag moth

Description

Common bag moth caterpillars are black or brown with a white speckled head or thorax and can grow up to 80mm long. Bag moth caterpillars live in mobile silk bags that hang from the trees and shrubs they eat. The bag is formed by the caterpillar, which spins a strong silk around itself incorporating twigs, bark, and vegetation from its plant host. This helps to camouflage the bag.

The caterpillar secures itself within the bag using hooks on its rear prolegs, allowing its head and thorax to emerge. The caterpillar uses its true legs to move and hold onto foliage while dragging the bag behind it as it forages for food. It can also lower itself down from branch to branch using silk threads.

The bag’s design can be used to determine the sex of the larvae. Male caterpillars incorporate vegetation all along the length of the bag while females place vegetation at the narrow end.

Adult females are flightless and grublike, and they remain in the bag. They die soon after laying eggs. The adult male is a fully winged moth, dark brown to black in colour with a wingspan of about 30 millimetres.