Silk-assisted hatching of the Japanese bagworm moth Eumeta variegata (Lepidoptera: Psychidae)

Bagworms constantly carry a portable bag with their prolegs inside, even when walking. Therefore, bagworms have a unique walking style. Bagworms construct footholds with silk and walk using only their thoracic legs. Bagworms build their bag immediately after hatching and carry them for the rest of their lives. Therefore, the only period when they move without a bag is immediately after hatching, when they move away from the hatched egg. We assessed their movement behavior in the period immediately after hatching when all legs were available, including prolegs. Our observations revealed that hatching Eumeta variegata (Japan's largest bagworm species) spun foothold silk threads even as they left the egg. From the moment the head broke out of the egg, larvae began spinning foothold silk threads. To do this, larvae twisted their anterior regions approximately 90° immediately before hatching. This finding indicates that larvae prepare to spin foothold silk threads during embryonic development.