As everyone knows, a fly tastes with its feet. Actually, the hairs on its feet. It drinks both food and drink with its proboscis, from the Greek pro--before, and boskein--to feed. Flies convert solid or semi-solid food to liquid by regurgitating stomach fluids onto the food, thus semi-digesting it!
Vincent G. Dethier says in his legendary book (which I highly recommend) To Know A Fly: "Like taxes, the fly is always with us. . . It has no sociological impediments to reproduction; its food supply is unlimited; its basic requirements, few. . . . So, if we must live together, if we cannot live in peaceful coexistence, . . . let us learn something about and from some of our fellow earthlings." He goes on to describe in humorous detail his various experiments on the sensory proclivities of flies.
January 2006: This fly, a hairy maggot blow fly (Chrysomya rufifacies) has landed on a dewy geranium leaf and is drinking. Dethier explains that a fly detects water to drink with the sense organs on its feet, but whether the fly drinks or not (whether it is thirsty) is determined by the fluid pressure within its body cavity, not being determined by osmostic pressure or salt concentration.
To Know a Fly by Vincent Dethier, Holden-Day, Inc. 1962 ISBN 0-8162-2240-1