Head spicule

Some aphids have minute spicules on the surface of their heads

Spicules give an aphid's head a rugose appearance. Most species do not have them, whereas others have them either dorsally on their heads or both dorsally and ventrally.

Faint spicules

Dorsal spicules. Focus up and down on the specimen to see if the spicules are present ventrally, as well as dorsally.

The spicules on the right side of the head have been darkened for emphasis. Note also the developed diverging antennal tubercles. Head spicules are typically found on aphids with antennal tubercles, especially those that are parallel or converging.
Prominent spicules

Spicules can sometimes be quite conspicuous.

These head spicules are quite conspicuous, darkened for extra emphasis. Note also the converging antennal tubercles.
Spicules absent

The absence of spicules makes the aphid head appear smooth.

Note the smooth, diverging antennal tubercles.

Head spicule

Some aphids have minute spicules on the surface of their heads

Faint spicules

Prominent spicules

Spicules absent