What sweet liquid is excreted by aphids and collected by ants?

What sweet liquid is excreted by aphids and collected by ants? Honeydew is the sugar-rich liquid aphids release while feeding on plant sap.

Aphids pierce the phloem, where sap is under pressure and contains abundant sugar but relatively little protein. They process large quantities to obtain nutrients, expelling the excess as honeydew through the anus. Although often called a secretion, it is more precisely an excretion.

Ants collect honeydew directly from aphids in a relationship called trophobiosis. Some ants stroke or “milk” aphids to encourage release, then protect them from predators such as lady beetles and parasitoid wasps. The aphids gain defense, while the ants gain a dependable carbohydrate source.

Honeydew can also be produced by scale insects, cicadas and other sap-feeding insects. It may encourage sooty mold on plants, and honey bees sometimes process insect honeydew into dark “forest honey.”