The Head
A housefly’s head is where its eyes, antennae and mouthparts are. Houseflies do not have teeth or the capacity to chew, so they must consume liquid food. If the food is already in liquid form, so much the better for them. If the food is solid, they must first digest it.
How A Fly Eats
Where humans digest food beginning in the mouth and then in the intestines and stomach, a fly begins digesting its food on the outside of its body. First, the fly uses its antennae to smell out its food and land on it. If food is too solid for the fly to consume, it will first mop up the bits that it can and then vomit saliva and digestive juices onto the food particle. Once the food particle is soft enough to eat, the fly then mops or sucks up both the food and the digestive juices with its mouthparts, and the food goes directly to its stomach. Sometimes, if a fly can’t digest the food completely, it sends the food to an inner sac called a crop, where it continues to be broken down until it can be ingested.
The saliva and digestive juices that a fly vomits onto its food are unhygienic and can carry disease. They may also stick to a fly’s legs, which is why you don’t want flies coming near your food—especially if the fly’s most recent meal was trash or rotting organic matter. If the fly lands, it may leave deposits of previous meals or its digestive fluids on your food.
How A Fly Sees
Flies have two complex eyes. These eyes are made up of thousands of individual simple eyes, which compile images into a mosaic of vision that allows the fly to see the slightest movements from every direction (which is why they are so often hard to swat). Additionally, they have three other simple eyes located between these two that detect light and help them to know which way is up.
