Definition
An aphid is any of various small, soft-bodied insects of the family Aphididae that have mouthparts specially adapted for piercing and feed by sucking.
Etymology. 1884, Anglicized from Mod.L. aphides, pl. of aphis, coined by Linnaeus, though where he got it and why he applied it to the plant louse are mysteries. The theory favored by OED as "least improbable" is that it derives from the pl. of Gk. apheides "unsparing, lavishly bestowed," in ref. either to the "prodigious rate of production" of the insects or their voracity. They also are known as ant-cows.
For images and discussion of winged versus wingless aphids, see: alate, apterous
Discussion
Aphids are important vectors of many plant diseases caused by viruses, such as papaya ringspot.