A fly regurgitating digestive juices. (Carlos Ruiz/CC BY-ND) ====================================================================== Imagine you're at a picnic and just about to bite into your sandwich. Suddenly you spot a fly headed your way, homing in on your food with help from its compound eyes and antennae. It manages to escape your swatting, lands on the sandwich and then seems to throw up on it! It can look kind of gross, but the fly might be just airing out its own digested food, or spitting on yours. Most of the over 110,000 known fly species have no teeth, so they cannot chew solid food....