Honeydew
To eat plant sap, the aphid or scale insect pushes its mouth parts into the plant. Plant sap is under pressure inside the plant. The pressure inside the plant pushes the sap into the insect. Sometimes the pressure is so great that the sap is forced out of the rear of the insect. This is how honeydew is made. The honeydew then drops from the insect and makes a sticky layer on the plant.