honeydew a sticky, sugary liquid exuded by some insects, especially aphids such as the common greenfly, which suck plant sap. Wherever these insects infest a plant thickly, there may be enough honeydew produced to drip onto the ground. This is one explanation given for the mysterious arrival of the manna on which the biblical Israelites fed in the desert. A car parked under a lime tree (Tilia, not Citrus) in summer will soon become covered with honeydew.
A few insects produce so much of the substance that it can be gathered and used as a sweetener. One such is the sugar-cane leaf-hopper, a pest of the sugar-cane crop in Hawaii.