The story
From kissing + bug: they often feed on the lips of human victims.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: Any of a number of haematophagous bugs belonging to the subfamily Triatominae that feed on the blood of vertebrates, including humans, and which are known for spreading Chagas' disease. Full definition →
From kissing + bug: they often feed on the lips of human victims.
Etymology from Wiktionary, CC BY-SA 4.0.