I raised German shepherds in the past, and I noticed they were always alert to sounds and vibrations, and smells. Later i learned they can hear your heartbeat and smell fear on you.
Just as a fly can sense sickness and death, they are attracted to that negativity.
Ba'al Zabub, Ba'al Zvuv or Beelzebub, also spelled Beelzebul or Belzebuth, and occasionally known as the Lord of the Flies, is a name derived from a Philistine god, formerly worshipped in Ekron, and later adopted by some Abrahamic religions as a major demon. The name Beelzebub is associated with the Canaanite god Baal. Beelzebub is known in demonology as one of the seven deadly demons or seven princes of Hell, Beelzebub representing gluttony and envy. The Dictionnaire Infernal describes Beelzebub as a being capable of flying, known as the "Lord of the Flies", "Lord of the Flyers", or the "Lord of the Flying Demons.
In the realm of the frequency of light and sight we can't see, who are you calling?