why do flies rub their hands together

Flies rub their hands (actually their front legs) together primarily as a grooming behavior to clean off dirt, debris, and leftover particles from whatever they landed on. Since flies have taste receptors on their feet, rubbing them helps clear away any build-up that might interfere with their ability to taste and smell their surroundings. This cleaning process allows them to effectively taste food before consuming it and keep their sensory hairs and receptors free from obstruction. Additionally, this behavior may help flies check their limbs for damage or prepare their legs for movement. The rubbing of their legs is not a sign of plotting or menace but an important part of their daily maintenance to stay clean and functional.