In Japan, it has long been customary to visit graves in mid-August, because people believe, on those days, deceased ancestors return from the other world to this world. We have to greet them properly. The reason for greeting is to thank them for watching over us and for being able to live safely on a daily basis. Failure to do so can lead to disasters, epidemics of bad illnesses, and poor crops.
Kunio Yanagita (柳田国男: 1875-1962) was a person who deeply studied the ancient Japanese folk customs. I found a description in his book the word “dragonfly first day（蜻蛉朔日）” .
The reason seems to be that many dragonflies of a species (scientific name: Pantala flavescens) appear around this time and that people thought these were the ancestors.
The dragonflies of this species, however, can be seen in Japan as the result of abortive migration in the ecological term. None of this species occur in Japan, and they all fly from Southeast Asia every year.
Although it is not from the other world, I feel that it is a mysterious story to actually fly from a distant southern country.
Source and link to National Diet Library (digital library)
Kunio Yanagita (1939). Folklore vocabularies of seasonal customs (in Japanese：柳田国男 (1939)。歳時習俗語彙).
