The fly was a predominant soul-symbol within many ancient religions. Many primitives believed that flies possessed souls of deceased persons, and by swallowing a fly the women conceived and bear children. Virgin mothers of Celtic heroes–Etain, Cuchulainn–conceived this way.
The Greeks similarly believed that souls traveled from one life to the next in insect form; their very word for soul, psyche, meant a butterfly. As in the Middle East, Baal-Zebub or Beelzebub was “Lord of Flies” because he was a psychopomp, his title really meant “Lord of Souls.”
Such ideas and images indicate a very archaic mode of thought, which predates the discovery of fatherhood. Women thought they conceived by themselves. Both men and women were attempting to imagine methods by which the fetus entered the woman’s body. A.G.H.
Source: 56, 316-317.