I often see these moths in the hedgerows when I go walking through the fields. These day-flying moths rest on the tops of leaves and fly slowly only a few meters when disturbed. They should therefore be easy prey for birds, but are distasteful (containing toxins). They are called hotaruga in Japanese – hotaru means firefly so perhaps they are supposed to resemble fireflies (can’t quite see it myself).
Pidorus atratus (hotaruga)